Compressor HVAC: Description and Operation
COMPRESSOR
The compressor is driven by the drive belt from the crank pulley of the engine. If the compressor is activated each time the engine is started, this causes too much load to the engine. The magnetic clutch (1) transmits the power from the engine to the compressor and activates it when the air conditioning is ON. Also, it cuts off the power from the engine to the compressor when the air conditioning is OFF.
When servicing the compressor, keep dirt or foreign material from getting on or into the compressor parts and system. Clean tools and a clean work area are important for proper service. The compressor connections and the outside of the compressor should be cleaned before any "On-Vehicle" repair, or before removal of the compressor. The parts must be kept clean at all times and any parts to be reassembled should be cleaned with Trichloroethane, naphtha, kerosene, or equivalent solvent, and dried with dry air. Use only lint free cloths to wipe parts.
The repair operations described are based on bench overhaul with compressor removed from the vehicle, except as noted. When the compressor is removed from the vehicle for servicing, the oil remaining in the compressor should be discarded and new compressor oil added to the compressor.
Compressor malfunction will appear in one of four ways: noise, seizure, leakage or low discharge pressure. Resonant compressor noises are not cause for alarm; however, irregular noise or rattles may indicate broken parts or excessive clearances due to wear. To check seizure, de-energize the magnetic clutch and check to see if the drive plate can be rotated. If rotation is impossible, the compressor is seized. Low discharge pressure may be due to a faulty internal seal of the compressor, or a restriction in the compressor. Low discharge pressure may also be due to an insufficient refrigerant charge or a restriction elsewhere in the system. These possibilities should be checked prior to servicing the compressor. If the compressor is inoperative, but is not seized, check to see if current is being supplied to the magnetic clutch coil terminals.
The compressor oil used in the HFC-134a system compressor differs from that used in R-12 systems. Concerning the types of compressor oil which are used for the vehicle, see "Specifications". Mechanical Specifications Also, compressor oil to be used varies according to the compressor model. Be sure to avoid mixing two or more different types of oil.
If the wrong oil is used, lubrication will be poor and the compressor will seize or malfunction.
DKV-14D Type Compressor
DKV-14D is equipped with five-vane rotary compressor.
The compressor has vanes built into a to rotor which is mounted on a shaft.
When the shaft rotates, the vanes built into the cylinder block assembly are operated by centrifugal force. This changes the volume of the spare formed by the rotor and cylinder, resulting in the intake and compression of the refrigerant gas. The discharge valve and the valve stopper, which protects the discharge valve, are built into the cylinder block assembly. There is no suction valve but a shaft seal is installed between the shaft and head; a trigger valve, which applies back pressure to the vanes, is installed in the cylinder block and a refrigerant gas temperature sensor is installed in the front head.
The specified quantity of compressor oil is contained in the compressor to lubricate the various parts using the refrigerant gas discharge pressure.
The thermo sensor is installed to the front head of the compressor to protect it by stopping its operation when the refrigerant gas is insufficient or when the temperature get abnormally high.
- OFF: 160 ± 5 ° C (320.0 ± 9.0 ° F)
- ON: 135 ± 5 ° C (275.0 ± 9.0 ° F)
FUNCTION
The compressor performs two main functions:
It compresses low-pressure and low-temperature refrigerant vapor from the evaporator into high-pressure and high-temperature refrigerant vapor to the [1][2]condenser.
It pumps refrigerant and refrigerant oil through the air conditioning system. This vehicle is equipped with a five-vane rotary compressor (3).
The thermo sensor (2) is installed to the front head of the compressor to protect it by stopping its operation when the temperature is abnormally high.
- OFF - 160 ± 5 °C (320.0 °C ± 9.0 °F)
- ON - 135 ± 5 °C (275.0 °C ± 9.0 °F)
The specified amount of the compressor oil is 150 cc (5.0 fl oz).
The oil used in the HFC-134a system compressor differs from that used in R-12 systems.
Also, compressor oil to be used varies according to the compressor model. Be sure to avoid mixing two or more different types of oil.
If the wrong oil is used, lubrication will be poor and the compressor will seize or malfunction.
The magnetic clutch connector is a waterproof type.
COMPRESSOR CONTROL
Electronic Thermostat
The electronic thermostat senses the temperature of cool air from the evaporator by means of the evaporator temperature sensor. This information determines whether the thermostat will provide ground to the thermo switch relay. When the temperature becomes too low, ground is not provided.
OFF: Below 1.0 ± 0.5° C (33.8 ± 0.9° F)
ON: Above 3.5 ± 0.3° C (38.3 ± 0.5° F)
A/C Compressor Clutch
With the engine running, battery voltage is applied to the A/C switch, the micro switch, the A/C triple pressure switch, and the coil of the A/C compressor relay. When you press the A/C switch or set the controls to defrost, battery voltage is applied to the electronic thermostat. The solid-state switch in the electronic thermostat closes, providing a path to ground for the thermo switch relay, with the fan control switch in any position except OFF. Voltage is also applied through the A/C triple pressure switch to the coil of the thermo switch relay. This closes the thermo switch relay contacts, applying battery voltage to the A/C ON input of the Powertrain Control Module (PCM). The PCM then provides ground for the A/C compressor relay. The A/C compressor relay contacts close, applying battery voltage to the compressor clutch through the closed contacts of the A/C thermo-switch. If either the A/C thermo-switch or A/C triple pressure switch opens, the compressor clutch disengages.
A/C Triple Pressure Switch
To prevent compressor damage, the triple pressure switch will open if system pressure is too low or too high: 176.5 ± 19.6 kpa (156.4 ± 17.7 psi.) or above 2942 ± 196.1 kpa (426.6 ± 28.4 psi). The medium pressure switch will close when system pressure exceeds 1471 ± 98.1 kPa (213.3 ± 14.2 psi), turning on the condenser fan.
Condenser Fan
With the engine running, battery voltage is applied to the A/C switch. When the A/C switch is pressed, battery voltage is then applied through the A/C triple pressure switch to the coil side of the condenser fan relay, which is continually grounded. Once the relay is energized, the contacts close, allowing battery voltage from the COND. FAN fuse to be applied to the condenser fan. The motor, being grounded continually, is energized, and the fan is activated.