1991 Sie rra GMC AC control problem

Compressor clutch not engaging Ricks Free Auto Repair Advice

Knowing make model and year would help. Most newer vehicles, 2000 and newer, will adjust the idle control up to compensate for the compressor engaging. Possible there is an issue in the idle air control valve or electrical circuit.

ac compressor clutch coil open or short. wire cut or open to ac clutch.2 wires one is ground the other power, remove connector ac compressor then probe with test light between the two wire

Trace the clutch wires from the compressor clutch to the nearest plug that you can disconnect. With the engine running, and the AC set to max, check to see if the clutch is engaged. If not, unplug the clutch wires and check the voltage going to the clutch. If the voltage is around 12 volts or more, then your clutch is shot and you will have to replace the clutch and compressor (sold as one unit). If the voltage is low or zero, then your AC is not calling for the compressor to run...a pressure or temperature sensor in your AC is out. Hope this helps.

Locate wires coming from compressor clutch and trace to nearest plug that you can unplug. Turn on A/C to max cooling. If clutch not engaged (center of compressor drive pulley not spinning with pulley), unplug compressor clutch wires and use multimeter to check voltage going to compressor clutch. If voltage is around 12 volts or more, then clutch should be engaged when plugged in. Plug clutch wires back in (with motor still running and ac set to max). If clutch still not engaged, then clutch definitely bad because 12V signal should engage it.

CHECK AC COMPRESSOR CLUTCH SHOULD BE ENGAGED OR RUNNING WITH AC SWITCH ON POSITION.IF NOT CHECK AC COMPRESSOR CLUTCH FUSE AND RELAY.IF BOTH GOOD AND POWER IS GOING TO AC CLUTCH.YOUR CLUTCH IS OPEN.IF ALL LOOKS GOOD YOUR AC LOW PRESSURE SWITCH IS BAD.COMPRESSOR SEIZED OR YOU HAVE TOO MUCH MOISTURE IN AC SYSTEM.

The follwing is a cut and paste from a service bulletin:

Bulletin No.: 461202

Date: May, 1994

SUBJECT:
A/C CONTROL HEAD FLASHES OR ERRATIC OPERATION OF A/C CONTROLS (POLISH
TERMINALS)

MODELS:
1988-94 CHEVROLET AND GMC TRUCK C/K MODELS
1990-94 CHEVROLET AND GMC TRUCK TOPKICK/KODIAK MODELS WITH C60 OR C69 AIR
CONDITIONING

CONDITION:

A/C Control Head flashes, performs erratically or malfunctions.

CAUSE:

Light surface corrosion on the Control Head terminals.

CORRECTION:

Remove the A/C Control Head and while holding the unit with the terminal
cavity down (toward the floor) so no particles will fall inside on the
circuit boards, polish the terminals on both sides of the cavity with a lead
pencil pink eraser. Do not use an ink eraser or other abrasive such as a
small wire brush or sandpaper, etc. Doing so will remove the terminal
coating and degrade the contact surface.

Performing this procedure, in many cases, will make replacing the Control
Head unnecessary. Using this procedure in conjunction with the A/C circuit
diagnosis found in the Electrical Diagnosis Manual and especially before
replacing a Control Head for any reason is recommended.

After polishing the Control Head terminals, but before reconnecting, check
for proper terminal contact as described in the applicable electrical
diagnosis manual. If contact is good, apply dielectric grease (P/N 12345579)
to the harness connector terminals. Please do not apply grease to the
Control Head.

scott it sounds like you might have a small leak. most a/c units will not engage the compressor clutch if there is no refrigerant. I would goto autozone and use a leak detention kit before I would do anything. Normally when you fill it up then you will hear the clutch engage... let us know

have you tested for voltage at the compressor?

It may have a bad AC clutch, or a wire is split somewhere in the harness. check for appropriate voltage at the compressor.

you mayyy need a new compressor if you infact have voltage to it

check the fuse first then check the wiring inside then that is OK then check the wire on the compressor it self, its a connector might have to pull  it off and then on. pulling off the compressor is a big deal its lines are a sealed system, the refrigerant lines are under pressure