Ac compressor not engaging

Griffco77 · May 10

Hi im nate new to forum. I have an 05 colorado 4cyl standard and the ac compressor clutch won't engage.

Fuse is good, relay is good. If I take the relay out and jump across relay clutch engages. Does any one know why im not getting power there. I checked the pressure sensor switch 5v on 1 wire

Good ground and when I check the last twire it beeps ground fast like beep beep. Etc if u have a power probe u can understand what im talking about. I tried to jump pressure switch but dont know if im doing it right

Please help I cant afford to pay someone to chase wires and track it done.

davester · May 10

charm.li (website) has wiring diagrams, connector pinouts and diagnostic procedures you can use to find what the problem is.

It's possible the ac pressure sensor isn't working right, or is the pressure in the ac system is too low for the clutch to engage (just some common things, it could be other stuff as well).

Griffco77 · May 10

Just more on first post i disconnected the ac compressor and just hooked up a light. The only way I could get the light to come on was to jump the relay. I

Dont know alot about elec. Diagnosis so im not sure if this would work because of the pressure sensor if anyone knows please let me know ow.

asilverblazer · May 11

On 5/9/2026 at 9:29 PM, Griffco77 said:

Fuse is good, relay is good. If I take the relay out and jump across relay clutch engages. Does any one know why im not getting power there.

Please help I cant afford to pay someone to chase wires and track it done.

On 5/9/2026 at 11:51 PM, Griffco77 said:

I Dont know alot about elec. Diagnosis so im not sure if this would work because of the pressure sensor if anyone knows please let me know ow.

The relay isn't powering the clutch because the computer is telling it not to. Likely because the refrigerant charge is low and is protecting the compressor.

It will need a set of pressure gauges to confirm a low charge.

Then the cause of the lost refrigerant would need to be found and repaired. Followed by vacuuming the system down and adding new (correct amount) refrigerant.

If you have confirmed the refrigerant charge is correct, the only reason for the relay not to power the compressor is the relay itself is bad or bad wiring. In the case of the latter - you will have to manually trace the wires looking for faults. If you're lucky you might find something obvious like rodent damage. In any case, the likely problem is low charge.

Griffco77 · May 11

The old compressor was bad put in. New one put vacuum o it and confirmed no leaks. Went to charge and it would only take a little bit cause new compressor clutch wouldn't engage what do I do jump relay to get compressor going to finish filling. Filling by 12 ounce can it would only take maybe 4 or 6 ounces

Should I jump relay and get compressor going to finish filling.

asilverblazer · May 12

17 hours ago, Griffco77 said:

The old compressor was bad put in. New one put vacuum o it and confirmed no leaks. Went to charge and it would only take a little bit cause new compressor clutch wouldn't engage what do I do jump relay to get compressor going to finish filling. Filling by 12 ounce can it would only take maybe 4 or 6 ounces

Should I jump relay and get compressor going to finish filling.

The cans should be pressurized enough to 'push' refrigerant in, especially when the system is under vacuum where it should 'pull' the refrigerant in.

It is a careful sequence of operations to suck down the system and add refrigerant while maintaining the original vacuum and replacing it with only refrigerant. All while not allowing atmospheric air to enter.

Having a digital scale handy to measure the refrigerant can before opening it and after to make sure the correct amount of refrigerant entered the system. Proper charge is determined by weight - not volume.

Presumably, you are using the proper gauges and vacuum pump necessary.

Edited May 12 by asilverblazer