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MX Systems, LLC FAQ

  1. General FAQ's
    1. Why do I have to change my condenser when my compressor fails?
    2. Why do I have repeated clutch failures?
    3. When you connect your manifold gauge set to your vehicle with the engine off, both gauges show pressure. What does this mean?
    4. When I replace my compressor, what other parts should I be replacing?
    5. When charging, what should my low and high side pressure be?
    6. What's the minimum static pressure I need for the compressor to operate?
    7. What static pressure should I expect to see?
    8. What should the high side pressure be?
    9. What is your privacy policy?
    10. What is the difference in PAG oils?
    11. What good is a static pressure reading then?
    12. What do all the numbers on the high and low side gauge mean?
    13. Should I test with doors open or closed, high idle, blower on high or low?
    14. If 30 PSI is a good low side pressure, then why isn't the system cooling?
    15. I can hear my compressor clutch engage, but the air out of my vents is warm. What is wrong with my air conditioning system?
    16. How much refrigerant does my vehicle hold?
    17. How do I vacuum my air conditioning system?
    18. How can I tell if the orifice tube is clogged?
    19. How can I tell if the compressor is bad?
    20. Hose Crimp Specification
    21. Does the orifice tube have to be installed in a specific direction?
    22. Can I use PAG oil on my O-Ring’s?
    23. Can I tell if the system is full with a static pressure reading?
  2. Automotive Troubleshooting
  3. Truck Troubleshooting
  4. Shipping & Returns
    1. When will my order ship?
    2. What shipping options are available?
    3. How are returns handled?
    4. Do you ship outside the continental U.S.?
  5. Privacy
    1. Communications
    2. Brochure Mailing List
    3. Communications to Serve You
    4. Fraud Protection and Compliance with Law
    5. Service Providers
    6. Special Events
    7. Business Transfers
    8. Cookies, IP Addresses, Pixel Tags and Tracking Technology
    9. Use of Aggregate Information
    10. Links
    11. Security
    12. Notification of Policy Changes
    13. Updating Personal Information
    14. Contacting Us
  6. Ask an Expert
  7. Limousine Troubleshooting
    1. Troubleshooting With Gauges
    2. Rear Air Conditioning Troubleshooting Guide
    3. Insufficient Rear Unit Heating
  8. Bus Troubleshooting
    1. Troubleshooting With Gauges

General FAQ's

Q: Why do I have to change my condenser when my compressor fails?

Current design condensers are built using micro-channel tubing. The tubing is so small it is imposable to flush contaminants out of the condenser. Failing to replace the condenser can cause debris for previous failures to circulate through the system contaminating the system and can cause catastrophic failures.

Q: Why do I have repeated clutch failures?

There are two major issues that can cause clutch failure, high head pressure and low voltage issues. The most common is high head pressure. If you have a vehicle that has multiple clutch failures, high head pressure could be the reason you are seeing this. Specialty vehicles such as limousines, stretched SUV’s and buses utilize remote mounted condensers. Some of the problems we have seen in the past are under sized condensers for the environment they are operating in, defective fans and fans that are under rated for the application. The second issue is low voltage. Vehicles that operate on a 12VDC system must be able to maintain 12VDC to the clutch. If the voltage is below 12VDC it can cause the clutch to slip and eventually seize. Either case can cause major damage to the compressor and to the air conditioning system.

Q: When you connect your manifold gauge set to your vehicle with the engine off, both gauges show pressure. What does this mean?

This is called static pressure. When the system is off, and temperature is stable, the pressure you see on both the high and low side gauges should be the same, or very close. Both the high and low side of the system have equalized.

Q: When I replace my compressor, what other parts should I be replacing?

Any time you are replacing the compressor you should also replace any gasket or o-ring from the open connections, replace the accumulator and/or the receiver drier, the orifice tube and clean or replace the expansion valve. In some cases you will even have to change the condenser.

In addition to replacing these components you should flush the a/c system using an approved flushing method and flush, you should use the correct type and viscosity of oil per the compressor manufacturers recommendations. Remember not all PAG oil is the same. Failure to replace the above components, flush the system and using the incorrect oil can cause secondary failure and may void you warranty.

Q: When charging, what should my low and high side pressure be?

This is the most asked question there is. There is no magic answer for this question though. There are too many variables. Compressor (engine) RPM and airflow across the condenser are always changing, thus engine speed is always affecting pressure. System design, blower speed, mode setting, refrigerant type, all cause variance in high and low side pressure. For this reason we simply can't say 30 on the low side and 200 on the high side. Though I might add, that's about where you'll usually end up. The reason 30 psi on the low side is just about right is because that translates into an evaporator temperature close to the freezing point of water. Look at your low side gauge and you'll see a temperature scale right next to your pressure scale. That low side pressure translates into evaporator temperature. Since moisture collects on the evaporator, we would like to keep the evaporator temperature slightly above the freezing point.

Q: What's the minimum static pressure I need for the compressor to operate?

Most systems will have a low pressure cut off switch that turns the system off at approximately 6 psi. The compressor will not function again until the pressure reaches approximately 34 psi. So, In most cases, you will need a static pressure of at least 34 psi before you begin to see the compressor operate.

Q: What static pressure should I expect to see?

Keep in mind that the static pressure changes based on temperature. Any change of temperature brings with it a change of pressure. The higher the ambient temperature, the higher the pressure will be. You can use a refrigerant pressure chart to find static pressures at various temperatures. Static pressure is not used to determine if a system is fully charged. Using your pressure / temperature chart you will see that if the R-134a system has a static pressure of 105 psi at 90 degrees F., we can then assume the system has some amount of liquid refrigerant. The system may or may not be full. At the same temperature, if the system showed only 85 psi, we could say with confidence, the system is low. This is because static pressures shown on a temperature chart would show inadequate pressure for the presence of any liquid refrigerant.

Q: What should the high side pressure be?

With R134a it's common to see high side pressure between 2.2 and 2.5 times ambient temperature. On a 90 degree day you should see pressure between 198 and 225 PSI on the high side of an R134a system. The system operates in a specific range based on outside ambient temperature. High side pressure has a broad range relative to temperature because of heat load on the evaporator, humidity, airflow across the condenser, and engine speed.

Q: What is your privacy policy?

Manex will never share any information with anyone that is gathered on our website.

Q: What is the difference in PAG oils?

PAG oil comes in several different viscosities PAG46, PAG100, PAG125 and PAG150. The higher the number the thicker the oil is. Every compressor manufacturer requires you to use the correct viscosity oil with their product. Failure to do so can cause catastrophic damage to your compressor.

Q: What good is a static pressure reading then?

By knowing your static pressure reading you will be able to determine if you have adequate pressure to activate your low pressure switch and enable the compressor clutch to engage. Static pressure can also be used to determine if a cylinder of refrigerant is contaminated with air. You can also determine if a system has enough pressure to begin leak testing. Your static pressure should be no lower than 50 PSI when leak testing.

Q: What do all the numbers on the high and low side gauge mean?

The low side pressure gauge (blue) is a compound gauge. This means it can be used to measure both pressure or vacuum. The numbers around the outside of this gauge indicate pressure in pounds per square inch (PSIG), and the numbers near the bottom indicate vacuum in inches of mercury (IHG). The smaller scales near the middle of the gauge list the temperature relationship of different refrigerants. Regardless of which refrigerant is being used, the scale designated as PSI is the one used to read system pressures when charging and diagnosing an a/c system. The working pressure of this gauge is from 0 to 120 PSI.

The high side gauge (red) is used to measure the high pressure side of the a/c system. This gauge has no markings that indicate vacuum. It reads positive pressure only. The working pressure of this gauge is also much higher than the low side gauge. The high side gauge reads from 0 to 500 PSI on most manifold gauge sets.

Q: Should I test with doors open or closed, high idle, blower on high or low?

We should measure high and low side pressure at stable engine speeds. This can be done at engine speeds just slightly above idle. (1,200 to 1,500 RPM is most often recommended) We like to test with the system in MAX position on high blower with the windows and doors closed. We would like to keep engine and exhaust heat from causing abnormal heat load on the evaporator.

Testing should be done with blower speed on high. Low blower speed will reduce heat load on the evaporator to the point where compressor cycling can occur. We want nice stable conditions when testing. When needed, low blower speed can be used to force low side pressure down during testing and adjustment of compressor cut-out pressure.

Q: If 30 PSI is a good low side pressure, then why isn't the system cooling?

Well, there are a couple reasons, but let's look at the most common. Let's take the orifice tube system for example. You can have a system evaporator pressure of 30 psi, and still be low on refrigerant. Let's assume that only half the evaporator is full of boiling, heat removing, liquid refrigerant. Only half the air traveling through the coil is being cooled. Pressure readings indicate core temperature is near thirty degrees, but half the core isn't removing any heat. The system is close to being full, but the discharge air is only slightly cool. On the fixed orifice tube system, most people will charge until the inlet of the evaporator, and the outlet of the evaporator are within a degree or two of each other. That indicates the quantity of refrigerant is enough that the entire coil is being used. At this point, the boiling liquid will spill into the accumulator, thus the outlet tube will be very cold. If the system has a TXV or H block, you will not be able to charge by feeling the evaporator outlet tube like we can on a fixed orifice tube system. The TXV is very efficient and is designed to tightly control liquid refrigerant from spilling out of the evaporator. The area we would measure is in the evaporator box, and not accessible for this purpose.

Q: I can hear my compressor clutch engage, but the air out of my vents is warm. What is wrong with my air conditioning system?

There are several possibilities why your compressor clutch would engage and your louver temperature be elevated. The major reason would be your system is in a superheat condition. Superheat condition means there is not enough liquid refrigerant in the evaporator to effectively transfer the heat. This condition is caused by one of two reasons. One there is a restriction of flow to the evaporator or the second a low refrigerant charge.

The best method to test this is to add a small amount of refrigerant to the system, between 2-4 ounces, depending on the total system charge. If adding the refrigerant corrects or improves the issue, you most likely have a refrigerant leak and the system should be recovered, have the leak repaired, vacuum and recharge the system with the original factory specified amount of refrigerant. If adding the refrigerant did NOT improve your cooling, you most likely have a restriction within the refrigerate circuit. The restriction could be in the condenser, drier or accumulator, expansion valve or orifice tube. The system will have to be diagnosed in order to determine the real problem.

Q: How much refrigerant does my vehicle hold?

This is a tricky question, it all depends on the vehicle you are working on. For your everyday cars and trucks please refer to the OEM specifications for this information. For specialty vehicles such as limousines and stretched SUV’s use the following as a guideline, OEM charge specification plus 1 pound for each auxiliary evaporator. For school bus and shuttle bus applications it is best to charge by your gauges and paying close attention to your delta-t. The delta-t is the temperature differential across your evaporator core. As you increase your charge you should also see your delta-t expand. When it gets to the point that adding more refrigerant does not effect the delta-t your system is fully charged.

Q: How do I vacuum my air conditioning system?

In order to vacuum the air conditioning system correctly you will need a recovery / recycle machine or a standard manifold gauge set and a vacuum pump. We strongly encourage that you use a minimum 5 CFM Dual Stage Vacuum Pump. Start by making sure all your valves are closed. With the manifold gauge set connected to the air conditioning system (red to the high side / Blue to the low side) connect the yellow hose to the vacuum pump. Start the vacuum pump and open both valves completely. This will insure that vacuum is being pulled throughout the air conditioning system. After 15 Minutes close both valves and shut off the vacuum pump. Watch the low side gauge reading, making sure that the needle does not rise. It the needle rises you have a leak. At this point you will need to find and repair the leak. If the needle does not rise you have a sealed system and you need to continue to vacuum the system. Start the vacuum pump, open both valves and vacuum for 1 hour. After you have completed the vacuum close the valves shut off and remove the vacuum pump. Your system is now ready to be charged with refrigerant oil and refrigerant.

Q: How can I tell if the orifice tube is clogged?

A restricted orifice will usually show as very low suction side pressure and lower than normal high side pressure. When the compressor clutch engages, the suction against the restricted orifice will cause the compressor to quickly cycle out. After compressor clutch disengagement, the rise in suction side pressure will usually be very slow. Rapid compressor disengagement and slow engagement may indicate a clogged orifice. A clogged orifice tube will starve a compressor of oil.

Q: How can I tell if the compressor is bad?

Usually the compressor will show the inability to generate enough suction and pressure at or near idle speeds. If the engine speed needs to be increased substantially to bring the system pressures in range, that's a sign that the compressor is getting weak.

Sometimes it's very simple. If we hook the gauges up and see 80 psi on the low side, and 80 psi on the high side, and the compressor hub is spinning, it's likely that compressor is not producing suction, and is not producing pressure. We could add or remove refrigerant and still nothing would happen. The compressor must be able to pull a vacuum, and create pressure. Compressors that use a variable stroke are often misdiagnosed as being defective, when only the internal pressure control device is at fault.

Q: Hose Crimp Specification

Q: Does the orifice tube have to be installed in a specific direction?

Yes, the orifice tube is designed to be installed in a specific direction. If you look at the orifice tube you will notice that there is a long end and a short end. Both ends are built with a screen, the long screen is the inlet of the orifice tube and the short end is the outlet. The long end of the orifice tube should be pointed toward the Condenser and the short end toward the evaporator. Most orifice tubes are equipped with an arrow that indicates the direction of refrigerant flow.

Q: Can I use PAG oil on my O-Ring’s?

NO, there are only two types of oil recommended for use on o-rings. Mineral oil (same oil that was used in the old R-12 systems) and O-Ring Lube that is a silicone based product. When PAG oil is used it gets on the threads of the fitting connection resulting in a chemical reaction between the oil, the moisture in the air and the oxygen. This reaction creates and acid the eats away at the threads or seizes them. When you try to service the unit you either twist off the threads or twist the tubing resulting in more damage to the system.

Q: Can I tell if the system is full with a static pressure reading?

No. You can determine if there is liquid refrigerant in the system, but you will not be able to tell how much liquid it contains. For example, a thirty pound cylinder of R134a refrigerant will show the same pressure whether it has thirty pounds or 1 pound in it. With static pressure, you will only know if the system has some amount of liquid refrigerant present.


Shipping & Returns

Q: When will my order ship?

Orders received by 2PM local time typically are processed the same day received. Shipping times will vary depending on your location and selected shipping options. Typical shipping times range from 1-5 days and may vary during the holiday season. For UPS shipments you can track the progress of the order using their order tracking number available on your order. Shipping delays can occur when the wrong address or zip code is submitted for the shipping address. If the shipping company cannot deliver the package we will contact you via phone or e-mail.

Q: What shipping options are available?

MX Systems, LLC offers our customers the option of selecting 2 day ground, next day, or air through either the United States Postal Service USPS) or United Parcel Service (UPS) for shipments in the continental U.S.

Q: How are returns handled?

If an items needs to be returned, the customer is responsible for the return shipping fees and should obtain a Return Merchandise Authorization (RMA). Please contact our Customer Service Department at 800-527-0481 to discuss the reason for the return and make the necessary arrangements. The amount of the refund will be based on the purchase price of your products and may include a restocking fee.

Q: Do you ship outside the continental U.S.?

We apologize for any inconvenience but we do not currently ship outside the continental U.S. We do not ship to Canada, Alaska, Hawaii, Puerto Rico or other U.S. Territories, or international locations at this time.

Privacy

Q: Communications

If you select during the order process or at other times when you submit personally identifiable information, the information you provide may be used by MX Systems, LLC to create and deliver to you our newsletters, surveys or other communications containing product information. If you prefer not to receive such Communications, please do not select the ‘Please inform me option’. If you do select this option and later decide that you would no longer like to receive these communications, please use the features made available to you.

Q: Brochure Mailing List

If you have requested a MX Systems, LLC brochure, all information is kept completely confidential and is not shared with any third parties. We may, on occasion, send you an updated catalog or brochure. If you do not wish to receive any mail from MX Systems, LLC, please contact us via email at hazel@mxheatcool.com. Include your name and mailing address and email address. You will be removed from any future mailings.

Q: Communications to Serve You

If you have elected to provide us with your contact information, e.g., by registering at the Site, emailing our Customer Service department or placing an order, we may provide you with service related announcements concerning the Site or contact you regarding your customer service requests or your order. For example, all registered users will receive an email to confirm their order. These types of communications are necessary to serve you, respond to your concerns and to provide the high level of customer service that MX Systems, LLC offers its customers.

Disclosure of Personally Identifiable Information

We will never provide your personally identifiable information to third parties for their use in marketing their products or services to you without your consent. MX Systems, LLC takes great pride in having you as a customer and we will ensure your privacy as a customer. MX Systems, LLC does not sell or exchange names or any other information about our customers with third parties.

Q: Fraud Protection and Compliance with Law

We may disclose any information, including personally identifiable information, we deem necessary, in our sole discretion, to comply with any applicable law, regulation, legal process or governmental request. We may also exchange information, including personally identifiable information, with other companies and organizations for credit fraud protection and risk reduction.

Q: Service Providers

We may retain other companies and individuals to perform functions consistent with our Privacy Policy on our behalf. Examples include customer support specialists, web hosting companies, fulfillment companies (e.g., companies that fill product orders or coordinate mailings), data analysis firms and email service providers. Such third parties may be provided with access to personally identifiable information needed to perform their functions, but may not use such information for any other purpose.

Q: Special Events

If you elect to participate in any promotions, sweepstakes, surveys, questionnaires or other events during your visit to our Site, the rules or terms and conditions for those events may indicate that your personally identifiable information will be shared with third parties. By choosing to participate and submitting your personally identifiable information with respect to such events, you consent to disclosure of your personally identifiable information to such third parties.

Q: Business Transfers

As we continue to develop our business, we might sell certain of our assets. In such transactions, user information, including personally identifiable information, generally is one of the transferred business assets, and by submitting your personal information on the Site you agree that your data may be transferred to such parties in these circumstances.

Q: Cookies, IP Addresses, Pixel Tags and Tracking Technology

We may place a "cookie" on your computer's hard drive so we can recognize you as a return user and personalize your experience. A cookie is a piece of data that enables us to track and target your preferences. The cookie will be stored on your computer's hard drive until you remove it. We may also use temporary or "session" cookies to help you shop. These cookies will expire when you place an order. You can have your browser notify you of, or automatically reject, cookies. If you reject our cookies, you may still use the Site, but you may be limited in the use of some of the features. In addition, we may use IP addresses to analyze trends, administer the Site, track traffic patterns, and gather demographic information for aggregate use, as well as in combination with your personally identifiable information for credit fraud protection and risk reduction.

Similarly, when you visit this Site or view one of our emails, we may use pixel tags (also called "clear" gifs), tracking links and/or similar technology to note some of the pages you visit on our Site and personalize your experience. We may also use pixel tags to determine what types of email your browser supports. We may use the information collected through pixel tags, tracking links and similar technology in combination with your personally identifiable information.

YOUR DOMAIN NAME HERE does recognize your ISP (internet service provider), however, we cannot identify you as an individual. If you make an on-line purchase we do collect information (such as sales statistics and traffic patterns) to help improve your shopping experience. We keep all information confidential.

Q: Use of Aggregate Information

We may use the information you provide in aggregate (non-personally identifiable) form for internal business purposes, such as generating statistics and developing marketing plans. We may collect, store or accumulate certain non-personally identifiable information concerning your use of the Site, such as information regarding which of our pages are most popular. We may share or transfer non-personally identifiable information with or to our affiliates, licensees and partners.

Q: Links

This Privacy Policy applies only to the information collected on this Site. Our Site may contain links to or from other websites and you should be aware that we are not responsible for the privacy practices of other websites. We encourage you to read the privacy policies of other websites linked to the Site.

Q: Security

MX Systems, LLC seeks to protect the security of your personal information both online and offline. All credit card transactions are secure. Every on-line order is encrypted and sent through a secure server, using SSL technology to prevent information from being intercepted.

Confidential information such as your credit card number will be used only to fulfill your order. To protect your privacy, we will ask you to enter your credit card number and expiration date each time you place an order with us. This way, even if someone else accesses the account information stored on your computer, they won't be able to use your credit card.

E-mail is not encrypted and is not a secure means to transmit credit card numbers. We will only display the last 4 digits of your credit card number on your account.

Q: Notification of Policy Changes

MX Systems, LLC reserves the right to revise this Privacy Policy in the future by posting changes at this location and we may make changes at any time without notification.

Q: Updating Personal Information

If you are a registered member at MX Systems, LLC, you can change your personal information at any time by updating your information at check-out.

Q: Contacting Us

We welcome your comments and questions about privacy. Please send email to hazel@mxheatcool.com.

We are confident that your visit to MX Systems, LLC is secure and safe. However, you may choose to call us directly to place your order over the telephone. Please call Customer Service toll free at 800-527-0481.


Limousine Troubleshooting

Q: Troubleshooting With Gauges

Q: Rear Air Conditioning Troubleshooting Guide

This procedure assumes the person performing the service work is a qualified air conditioning service technician. If there is any question about the following procedures please call Manex Corporation prior to performing any service work.

Insufficient Rear Unit Cooling

  1. Determine if the problem is low air output from the louvers or if the air temperature. If the problem is air temperature, proceed to step 2, if not proceed to step 7.

  2. To determine the extent of the problem insert thermometers in the dash air outlet and the most distant rear air outlet and the rear evaporator. Set the air conditioning systems on maximum cooling and high blower with the windows up. Run the engine at high idle (1500 RPM) for 15-20 minutes. Under normal conditions the temperature differential between the dash and rear evaporator should be between 5 to 7 degrees. Any temperature gain between the rear evaporator and the most distant louver can only be corrected with proper insulation of the duct hose and the vehicle. The actual temperatures will rise and fall relative to the ambient temperature, however the temperature differential should remain the same. For heat/cool units proceed to step 3, for cool only units proceed to step 4.

  3. If the rear unit is a heat/cool system, check the water valve controlling flow to the rear unit to be sure it is completely closed. If either hose at the rear unit is warm, a water bypass is occurring. Check the vacuum hoses that control the vacuum solenoid. The hose from the long port on the vacuum solenoid must go to the vacuum controlled water valve. The hose from the short port on the vacuum solenoid needs to go to the vacuum tee. Reversal of the connections will prevent the solenoid from venting in the cooling mode resulting in an open valve allowing the flow of HOT water to the rear unit during the cooling cycle. Adjust the control to the valve to insure full closure. If the problem persists, replace the valve. Proceed to step 4 if the water bypass was not the problem.

  4. Check the system refrigerant charge with the engine running at high idle (1500RPM) set the air conditioning controls on maximum cooling and high blower with the windows up. The charge should be checked using a combination of gauge reading and louver outlet temperature to determine the charge that will yield the best temperature. In many cases this type of system has better performance when it is slightly undercharged. Proceed to step 5 if refrigerant charge was not the problem.

  5. Evaluate the OEM portion of the air conditioning system to insure that all of the factory components are functioning properly and that the air discharge temperature of the dash louvers is adequate. Proceed to step 6 if the factory air conditioning system is functioning properly.

  6. Check all electrical connections to the rear unit, especially the ground connections, to insure solid connections. Voltage at the rear unit must be between 12.5 and 13.5 Volts DC. If the system has a solenoid control valve in the line going to the rear unit, check for proper operation. If the valve is being properly energized when current is applied you will hear a “CLICK” sound as the coil energizes. (The coil will be magnetized at this point) If these characteristics are not present, be sure the circuit is correct and good contacts are made. If the electrical coil on the valve is defective (draws excessive amps or does not engage valve), the coil only can be replaced without recovering the refrigerant. If the valve still will not function, repair or replace the valve.

    Check the liquid line from the condenser to the rear evaporator, if any portion of the line is cold to the touch or if it frosts up indicates a restriction. If a restriction is found, remove and clean or replace the component causing the problem. If the rear unit still does not cool repair or replace the expansion valve. It is important to remember that when an expansion valve or any other system component is replaced which requires the recovery of refrigerant; ALL ACCUMULATOR & DRIERS in the system must be replaced prior to recharging the system.

  7. If the air output appears less then normal from the front and / or rear outlets, check to be sure at least 12.5 Volts DC is present at the blower motors. Check the duct hose connections at the louvers and evaporator to be sure they are properly attached. Check for collapsed duct hose to the air outlets and restricted return air ducts that could restrict air flow. A frozen evaporator coil will severely restrict air output. A heavily frosted or iced evaporator suction tube would usually indicate a frozen coil. An inoperative thermostat causes this condition.

Q: Insufficient Rear Unit Heating

  1. Check operation of the water valve controlling flow to the rear unit. Be sure it is fully open when the control is in the “FULL OPEN” position. Allow 15 minutes of engine operation with the water valve open, the hoses going from the valve to the rear unit should be very hot and the return hose to the engine will be hot to the touch but at a lesser degree.

    If air gets into the coolant system, an air pocket can occur in the rear heater coil stopping the flow of water.

    To purge:

    1. Get the engine up to operating temperature and turn on rear unit.
    2. Using duckbill clamps, pinch off the hose feeding the front heater between the “Y” or “TEE” and the heater coil. This will send the total pressure of the water to the rear unit, which will force the air out of the rear unit. Continue to run the engine for 3 to 5 minutes.

    If these conditions do not exist, there is a restriction somewhere in the system, which might be corrected. In extremely cold climates it might be advisable to insulate the water hoses to the rear unit. If there appears to be an air output problem see step 7 in the Insufficient Rear Unit Cooling section.