HVAC-02, Air Conditioning Troubleshooting and Repair Since I'm constantly receiving questions on 944 air conditioning systems, I figured it's time to come up with come helpful troubleshooting tips. Working on the 944 A/C system is no different than working on any other automotive A/C system. They have all the same components which function in the same manner as any other A/C system. First, if you're having a problem with the A/C system on your 944, there are two ways you can approach solving the problem. The first is to just start replacing components and hope you get lucky by replacing the faulty component the first time. The other method involves doing some actual testing to narrow down the cause of the problem. In order to properly test the A/C system and narrow down the possible causes of your problem, you're going to have to invest in a set of A/C gauges. Before we begin with the actual troubleshooting, to properly troubleshoot the A/C system, it's extremely helpful to understand how the automobile A/C cycle works.

So, we'll begin by discussing automotive air conditioning theory of operation. There are two basic types of automotive air conditioning systems. The type of system is determined by the device used to control the expansion of the high pressure, high temperature liquid to a low pressure, low temperature liquid. One system uses and expansion valve while the other uses an orifice tube. 944s use an expansion valve system. We'll discuss the operation of both. The first component in the A/C cycle is the compressor. The compressor takes low temperature refrigerant gas and compresses it into a high pressure, high temperature gas. The refrigerant is then sent to the condenser which sits in front of the radiator. The condenser removes some of the heat from the refrigerant which causes the refrigerant to change phase from a hot gas to a warm liquid. In the expansion valve A/C system, the warm liquid is then passed through a receiver-drier which removes moisture (via a desiccant in the drier) from the refrigerant to maximize the efficiency of the heat exchange capability of the refrigerant.

On 944s, the receiver-drier is a small canister (probably with a sightglass on top) located near behind the driver's side headlight (LHD cars). No phase change occurs as the refrigerant passes through the receiver-drier. From there, the refrigerant is then passed through the expansion valve. The expansion valve has a sensing line that is attached to the suction of the A/C compressor. air handling unit requirementsThe expansion valve senses the pressure at the suction of the A/C compressor and modulates to maintain the pressure at the compressor suction. best prices on air conditioning unitsOn 944s, the expansion valve is located near in the passenger's footwell (LHD cars) near the center console next to the firewall.how to size an air handling unit

In the orifice tube system, the warm liquid refrigerant passes directly from the condenser to the orifice tube. The orifice tube is a fixed expansion device. The pressure drop across the orifice tube is proportional to the pressure into the orifice tube. So, the orifice tube system maintains the pressure at the suction of the A/C compressor by cycling the compressor on and off via a clutch. This is the type of system typically used by GM vehicles. The expansion of the warm liquid through the expansion valve or orifice tube causes a pressure drop and hence a temperature drop in the refrigerant. So, out of the expansion device we get a low temperature liquid refrigerant. The next component in the A/C system is the evaporator. Air from the passenger's compartment passes across one side of the coils in the evaporator. The low temperature liquid refrigerant passes through the other side of the coils. The refrigerant removes heat from the air in the passenger's compartment and returns to the A/C compressor suction as a low temperature gas (phase change).

In the orifice tube system, there is an accumulator located between the evaporator and the A/C compressor suction. The accumulator has moisture removal desiccant just like the receiver-drier used in the expansion valve system. However, it also collects any un-evaporated refrigerant to prevent liquid lock of the compressor. This can occur due to the cycling action of the compressor. The diagrams below show the two different A/C system cycles. The following is an general A/C system troubleshooting guide. Realize that it is generic and many of the things listed here may not apply to the 944. The following table is a general guideline for A/C system pressures and temperatures based on ambient outside temperature. Remember that these are a guideline and your actual temperatures and pressures will vary depending on humidity in the air and the condition of your system. A/C System Pressure Readings FREE Shipping on orders over $25. 75 used & new from There is a newer edition of this item:

Discover books for all types of engineers, auto enthusiasts, and much more. Publisher: Haynes Manuals, Inc.; 3rd Revised edition edition (December 4, 2000) 8.4 x 0.5 x 10.6 inches Shipping Weight: 13.6 ounces #699,739 in Books (See Top 100 in Books) 5 star42%4 star28%3 star19%2 star3%1 star8%See all 36 customer reviewsTop Customer ReviewsDisappointed and DepressedPerhaps updated for R143a?For Haynes...as well as how a DIYer like myself could diagnose his car's AC with just a ...Gave me the confidence to repair my cars ACVery usefullGreat manual if you already have some experience in Auto AC.exactly what I needed Automotive Electrical Manual (Haynes Repair Manuals) Automotive Heating and Air Conditioning (6th Edition) (Professional Technician)DIY Step by Step Automotive Air Conditioning Troubleshooting Procedures Air Conditioning System Noise Vehicle Specific Auto Repair Manual Replacement Procedure Any automotive air conditioning system employs four basic parts-a mechanical compressor, driven by the vehicle's engine;

an expansion valve, which is a restriction the compressor pumps against; and two heat exchangers, the evaporator and the condenser. In addition, there is the refrigerant that flows through this system. Avoid the need for an auto air conditioner service call. Theory of Air Conditioning How Air Conditioning Works The diagram shows the flow of R-134a Freon in an automotive air conditioning system. The freon is compressed and flows through the condenser where it is cooled into a liquid. The freon passes through the receiver/dryer to remove moisture. Once the freon leaves and enters the expansion valve/orifice tube The high pressure liquid becomes a vapor and is extremely cold as it passes through the evaporator and on to the compressor to repeat the cycle. Common Air Conditioning System Problems Only Hot air blows out the dash when I turn the Air Conditioning on. This is usually caused by a failing or failed Blend Door Actuator. The Actuator is usually located deep in the dash and attached to the hot/cold blend door.

The most common fix is to simply have it replaced. Of course this is after you have made certain that the rest of your air conditioning system is functioning properly. Listen for the AC Compressor to click in and out and feel the accumulator for cold temperatures. These are signs of a normal operating AC System. No air coming from air conditioning vents Check the air conditioner fuse and replace as necessary. Air conditioner system discharged. Have the system evacuated, charged and leak tested by an MVAC certified technician, utilizing approved recovery/recycling equipment. Air conditioner low pressure switch defective. Air conditioner fan resistor pack defective. Loose connection, broken wiring or defective air conditioner relay in air conditioning electrical circuit. Repair wiring or replace relay as necessary. Air Conditioner blows warm air Air conditioner system is discharged. Air conditioner compressor clutch not engaging. Check compressor clutch wiring, electrical connections and compressor clutch, and repair or replace as necessary.

Electronic Blend Door Actuator is not functioning which would only allow warm air to pass through vents. The AC lines going into the firewall would be cold if this id the case. Most common to replace actuator. Water collects on the interior floor when the air conditioner is used Air conditioner evaporator drain hose is blocked. Clear the drain hose where it exits the passenger compartment. Air conditioner evaporator drain hose is disconnected. Secure the drain hose to the evaporator drainage tray under the dashboard. Air conditioner has a moldy smell when used The air conditioner evaporator drain hose is blocked or partially restricted, allowing condensation to build up around the evaporator and drainage tray. Clear the drain hose where it exits the passenger compartment Find an auto repair manual for your car - Get instant access to your vehicles drive belt routing, complete wiring diagrams, trouble code information and other available updates and factory bulletins.