Heating and A/C System Description (Without Climate Control)

Heating and A/C System Description

The air conditioning (A/C) system removes heat from the passenger compartment by transferring heat from the ambient air to the evaporator. The A/C refrigerant expands in the evaporator, and the evaporator becomes very cold and absorbs the heat from the ambient air. The blower fan pushes air across the evaporator where the heat is absorbed, and then it blows the cool air into the passenger compartment.

This vehicle uses HFC-134a (R-134a) refrigerant, which does not contain chlorofluorocarbons. Pay attention to the following service items:

- Do not mix refrigerants CFC-12 (R-12) and HFC-134a (R-134a). They are not compatible.
- Use only the recommended polyalkyleneglycol (PAG) refrigerant oil (DENSO ND-OIL 8) designed for the R-134a A/C compressor. Intermixing the recommended (PAG) refrigerant oil with any other refrigerant oil will result in A/C compressor failure.
- All A/C system parts (A/C compressor, discharge line, suction line, evaporator, A/C condenser, receiver/dryer, expansion valve, O-rings for joints) are designed for refrigerant R-134a. Do not exchange with R-12 parts.
- Use a halogen gas leak detector designed for refrigerant R-134a.
- R-12 and R-134a refrigerant servicing equipment are not interchangeable. Use only a recovery/recycling/charging station that is U.L.-listed and is certified to meet the requirements of SAE J2210 to service the R-134a air conditioning systems.
- Always recover refrigerant R-134a with an approved recovery/recycling/charging station before disconnecting any A/C fitting.

A/C Pressure Switch

The A/C pressure switch consists of a high-low pressure switch (A/C pressure switch A) and a middle pressure switch (A/C pressure switch B).

- High-low pressure switch
If the refrigerant pressure becomes too high (due to blockage or lack of airflow at the condenser), or too low (due to leakage), the A/C pressure switch stops the A/C request signal to the PCM and the A/C compressor stops operating.

- Middle pressure switch
If the refrigerant pressure goes above 1,520 kPa (15.5 kgf/cm2, 221 psi), the A/C pressure switch closes to signal the PCM to change the speed of the A/C condenser fan and radiator fan to high. When the refrigerant pressure drops below 930 kPa (9.5 kgf/cm2, 135 psi), the A/C pressure switch opens to signal the PCM to change the speed of the A/C condenser fan and radiator fan to low.

A/C Pressure Switch Operation

NOTE: When the A/C system pressure is between the listed ranges, the pressure switches are in a transition state. The switch behavior depends upon whether the pressure is rising or falling.

Heating/Air Conditioning Door Positions

HVAC Control Unit Inputs and Outputs