A/C Pressure Transducer Test
Check electrical components1. Check all electrical wiring for wear or abrasions - especially if it passes through firewall or is located near hot engine parts. Check for blown fuses.
2. High pressure combination switch, which is located on the receiver-drier reservoir, is wired in series with the compressor magnetic clutch. It cuts off the electrical power supply to the clutch when refrigerant pressure drops below the control point of the switch.
Whenever the system is inactivated by the low pressure cut-off switch due to the loss of refrigerant, refrigerant oil may also have been lost. Therefore, to prevent damage to the compressor due to operation without sufficient lubrication, the leak must be repaired and the compressor oil level checked before final charge of the system.
The switch is a sealed, factory calibrated unit. No attempt shall be made to adjust or otherwise repair it. If it is found to be defective it must be replaced.
TO TEST THE SWITCH (Engine Off)
a. Remove molded rubber connector from the low and high pressure combination switch and jumper lead terminals together.
b. Press the A/C button with fan on low.
c. Momentarily turn the ignition switch on (do not crank the engine), listen for the compressor clutch engaging.
d. If the clutch does not engage, the clutch, the cycling clutch switch, wiring or fuse may be defective. Check the clutch circuit and clutch.
e. If clutch engages, connect the manifold gauge set and read evaporator suction pressure. At any pressure of 187 kPag (28 PSIG) and above, switch must actuate clutch.
If the evaporator suction pressure is below 170 kPag (25 PSIG) refrigerant system is low of charge or empty due to a leak. This check must be performed. For corrective action refer to refrigerant leak repair procedure.
f. Remove jumper, reinstall connector on switch and perform step number 3.
If the clutch does not engage, discharge the system, replace the switch, and recharge the system.
High pressure cut-out check
a. Disconnect the combination pressure switch electrical wires.
b. Check continuity between connectors on pressure switch. Since pressure switch is "normally closed", continuity should exist between the two connectors.
c. As a double check, by pass the high pressure cut-out switch. If compressor operates, now - but did not with pressure switch in circuit, replace pressure switch. If unit still does not operate properly, proceed as follows:
Check clutch
a. Remove connection between pressure switch and clutch lead.
b. Check continuity between clutch lead and ground. If continuity exists, clutch field is good.
Fan relay - with an ohmmeter, check continuity of relay per wiring diagram.
Blower motor.
Blower motor control switch.
Cycling clutch switch (CC switch)
The cycling clutch switch is located at the evaporator housing and is electrically in series with the compressor clutch coil. It is an on-off switch which turns the compressor on and off depending on the temperature sensed by the Freon charged capillary tube. The switch is a sealed specially calibrated unit and if found defective, must be replaced.