Truck A/C problem.

[Stinsok]

I thought it was low on refrigerant. It would start out cold and about 10 minutes later it would quit. I thought it may be freezing up. The compressor was not coming on. You can tap it with a wrench and it will start again (and blow cold.) Is it the switch or is the compressor clutch bad?

 

[Frank Tuesday]

Try to turn the clutch by hand. If it is easy to turn, your compressor is probably good.

Find the electrical connection to the compressor clutch coil. Turn the AC switch on and check if you have 12V.

If you have 12V present, check the continuity if the clutch coil. No continuity means your coil is bad.

If you don't have 12V, check the fuse and relay. Make sure they are fully seated. If these are both good (and properly seated), then you have a wiring fault, or a faulty switch in the control unit.

You can test continuity and voltage on the various branches from the fuse and relay. Get a wiring diagram to see where everything goes.

I'm a hobbyist mechanic, so grain of salt, but based on your description, I suspect your compressor is going bad. It just hasn't fully locked up yet. Second guess is a bad electrical connection.

I just did this with my car this weekend. I had two problems: bad switch in the control unit and a poorly seated relay. Both caused intermittent stopping of the AC.

 

[Stumbo]

Hey Frank,
My air takes longer and longer to get cold and now it's not getting as cold as it used to. Any thoughts?

 

[abracadunphy]

I know a guy ...

 

[Jeff Scott]

Real truck drivers don't use air conditioning...............

 

[two fingers]

I remember when we were kinda poor and dad's AC went out on his old pickup (circa 1977?). It stayed out all that summer because he couldn't afford to get it fixed. When my siblings and I complained he just grinned and said "We got 230 air conditioning. Roll down two windows and go thirty miles an hour."

 

[Frank Tuesday]

I know a guy ...

That was me this weekend. Replaced an engine mount, thermostat, and had to take out most of the dash and console to replace my A/C control unit. Tools everywhere. Any day you get to use an impact wrench and torque wrench is a good day.

 

[Frank Tuesday]

Hey Frank,
My air takes longer and longer to get cold and now it's not getting as cold as it used to. Any thoughts?

I don't. I only had a good answer for the OP is because I literally did just that this past weekend.

Have you checked your high and low side pressures? If you're leaking refrigerant, it could cause that problem. It could be 5 or 6 other things, too.

 

[hondo4life]

I just converted my 1988 truck to run R134a. I was so happy when it worked.
But it all leaked out after a couple of days because that old compressor has bad seals. I was so sad.
What was the question?

 

[megafiddle]

I thought it was low on refrigerant. It would start out cold and about 10 minutes later it would quit. I thought it may be freezing up. The compressor was not coming on. You can tap it with a wrench and it will start again (and blow cold.) Is it the switch or is the compressor clutch bad?

When you get it to work by tapping on it, can you hear the clutch engaging (a "clunk" and slight drop in engine RPM)?

If so, likely an intermittant electrical connection to the clutch. Make sure the connector is fully seated. Also unplug the connector and check that the contacts have not been pushed back into the connector housing.

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[megafiddle]

Hey Frank,
My air takes longer and longer to get cold and now it's not getting as cold as it used to. Any thoughts?

Typically that's a symptom of refrigerant loss. Unlike refrigerators and home air conditioners with unitized (and hermetically sealed) compressors, automobile compressors are externally driven and will eventually leak around the shaft. Could also be a leak elswhere in the system.

It really needs a proper diagnosis with a vacuum test.

Long ago, many would simply add freon, as needed, and never fix the leak. You could even buy recharging kits, which had dubious value at best. You really need to pump down the system first before recharging.

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[megafiddle]

Real truck drivers don't use air conditioning...............

That little sliding window in the middle of the rear window was one of the best option I ever had on a pickup.

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[Downunderwonder]

Unrelated to the OP, but a clogged cabin air filter messes with A.C. performance very well. Change them yourself very simply usually, empty glovebox and pop the latch, see your owner manual.