Principles of Operation
| WARNING | Carbon monoxide is colorless, odorless and dangerous. If it is necessary to operate the engine with the vehicle in a closed area such as a garage, always use an exhaust collector to vent the exhaust gases outside the closed area. Failure to follow these instructions may result in personal injury. |
| WARNING | R-134a is classified as a safe refrigerant, but misuse can make it dangerous. The following precautions must be observed. Failure to follow these instructions may result in personal injury. Always wear safety goggles when repairing an air conditioning system. Avoid contact with liquid refrigerant R-134a. R-134a vaporizes at approximately -25°C (-13°F) under atmospheric pressure and it will freeze skin tissue. Never allow refrigerant R-134a gas to escape in quantity in an occupied space. R-134a is non-toxic, but it will displace the oxygen needed to support life. Never use a torch in an atmosphere containing R-134a gas. R-134a is non-toxic at all normal conditions, but when it is exposed to high temperatures, such as a torch flame, it decomposes. During decomposition it releases irritating and toxic gases (as described in the material safety and data sheet (MSDS) from the manufacturer). The decomposition products are hydrofluoric acid, carbon dioxide and water. Do not allow any portion of the charged air conditioning system to become too hot. The pressure in an air conditioning system rises as the temperature rises and temperatures of approximately 85°C (185°F) can be dangerous. Allow the engine to cool sufficiently prior to carrying out maintenance or serious burns and injury can occur. |
| CAUTION | To avoid damaging the vehicle or A/C components, the following precautions must be observed. The A/C refrigerant of all vehicles must be identified and analyzed prior to refrigerant charging. Failure to do so can contaminate the shop bulk refrigerant and other vehicles. Do not add R-12 refrigerant to an A/C system that requires the use of R-134a refrigerant. These two types of refrigerant must never be mixed. Doing so can damage the A/C system. Charge the A/C system with the engine running only at the low-pressure side to prevent refrigerant slugging from damaging the A/C compressor. Use only R-134a refrigerant. Due to environmental concerns, when the air conditioning system is drained, the refrigerant must be collected using refrigerant recovery/recycling equipment. Federal law REQUIRES that R-134a be recovered into appropriate recovery equipment and the process be conducted by qualified technicians who have been certified by an approved organization, such as MACS, ASI, etc. Use of a recovery machine dedicated to R-134a is necessary to reduce the possibility of oil and refrigerant incompatibility concerns. Refer to the instructions provided by the equipment manufacturer when removing refrigerant from or charging the air conditioning system. Refrigerant R-134a must not be mixed with air for leak testing or used with air for any other purpose above atmospheric pressure. R-134a is combustible when mixed with high concentrations of air and higher pressures. A number of manufacturers are producing refrigerant products that are described as direct substitutes for refrigerant R-134a. The use of any unauthorized substitute refrigerant can severely damage the A/C components. If repair is required, use only new or recycled R-134a. |
| CAUTION | To avoid contamination of the A/C system: Never open or loosen a connection before recovering the refrigerant. When loosening a connection, if any residual pressure is evident, allow it to leak out before opening the fitting. Evacuate a system that has been opened to install a new component or one that has discharged through leakage before charging. Seal open fittings with a cap or plug immediately after disconnecting a component from the system. Clean the outside of the fittings thoroughly before disconnecting a component from the system. Do not remove the sealing caps from a new component until ready to install. Refrigerant oil will absorb moisture from the atmosphere if left uncapped. Do not open an oil container until ready to use and install the cap immediately after using. Store the oil in a clean, moisture-free container. Install a new O-ring seal before connecting an open fitting. Coat the fitting and O-ring seal with mineral oil before connecting. When installing a refrigerant line, avoid sharp bends. Position the line away from the exhaust or any sharp edges that can chafe the line. Tighten threaded fittings only to specifications. The steel and aluminum fittings used in the refrigerant system will not tolerate over-tightening. When disconnecting a fitting, use a wrench on both halves of the fitting to prevent twisting of the refrigerant lines or tubes. Do not open a refrigerant system or uncap a new component unless it is as close as possible to room temperature. This will prevent condensation from forming inside a component that is cooler than the surrounding air. |
There are four main principles involved with the basic theory of operation
- heat transfer
- latent heat of vaporization
- relative humidity
- effects of pressure
Normal Operation
The function selector switch directs vacuum to the appropriate vacuum control motor(s), controlling the door movement.
Under normal operation, when heat is selected on the temperature control switch and the blower motor switch is turned on, the blower motor directs air through the heater core. The heater core is filled with heated engine coolant.
Under normal operation, the A/C system is activated when the function selector switch is in the NORMAL A/C, MAX A/C, FLOOR/DEFROST, or DEFROST modes. The PCM controls the cycling of the A/C compressor clutch.
Under normal operation, the A/C system is activated when the function selector switch is in the NORMAL A/C, MAX A/C, FLOOR/DEFROST, or DEFROST modes. The PCM controls the cycling of the A/C compressor clutch.
Under normal operation, the temperature control switch actuates the temperature blend door through the temperature blend door actuator cable.
When the function selector switch is placed in any position except OFF, the blower motor will operate at the desired speed according to the position of the blower motor switch.
When the blower motor switch is placed in high and the function selector switch is in any position except OFF, the blower motor switch creates a direct link to ground for the blower motor, resulting in high speed operation.
Under normal conditions, when the blower motor switch is placed in the low, M1, or M2 positions and the function selector switch is in any position except OFF, the blower motor switch completes the circuit 261 (OG/BK) from the blower motor through the blower motor resistor, and to ground. The current flows through 1 to 3 resistors, depending on the selected blower motor speed.
Under normal conditions, when the function selector switch is in any position except OFF, the blower motor switch completes the circuit 261 (OG/BK) from the blower motor through either the blower motor resistor, or directly to ground.
Refrigerant Identification
- Follow the instructions included with the refrigerant identifier to obtain the sample for testing.
- The diagnostic tool will display 1 of the following: If the purity level of R-134a is 98% or greater by weight, the green PASS light emitting diode (LED) will light. The weight concentrations of R-134a, R-12, R-22, hydrocarbons and air will be displayed on the digital display. If the refrigerant R-134a does not meet the 98% purity level, the red FAIL LED will light and an alarm will sound alerting the user of potential hazards. The weight concentrations of R-134a, R-12, R-22 and hydrocarbons will be displayed on the digital display. If the hydrocarbon concentrations are 2% or greater by weight, the red FAIL LED will light, Hydrocarbon High be displayed on the digital display, and an alarm will sound alerting the user of potential hazards. The weight concentrations of R-134a, R-12, R-22 and hydrocarbons will also be displayed on the digital display.
- The percentage of air contained in the sample will be displayed if the R-134a content is 98% or greater. The diagnostic tool eliminates the effect of air when determining the refrigerant sample content because air is not considered a contaminant, although air can affect A/C system performance. When the diagnostic tool has determined that a refrigerant source is pure (R-134a is 98% or greater by weight) and the air concentration levels are 2% or greater by weight, the diagnostic tool will prompt the user if an air purge is desired.
- If contaminated refrigerant is detected, repeat the refrigerant identification test to verify that the refrigerant is indeed contaminated.