Compressor not turning on.

[Shawn Wheeler]

Hello, asking for some words of wisdom.

1984 K10
Turn AC on at the dash like normal. The compressor does not turn on.
Check the fuse = Good
Supplied 12 volts from the batter to the compressor, I can hear the clutch engage when power is applied. It disengaged when power was removed.
I also put my test probe on the wire that connects to the compressor when the dash slider was set to AC. No light on the test problem.

And this is the end of my knowledge.

Where should look next?

And now for a stupid question. As a stop gap, can I direct wire a switch to the compressor?

Thank you in advance for your help.

 

[Moodyalaskan]

From what I have read online, if system is low on refrigerant, pressure is low and compressor won't kick on.

 

[Shawn Wheeler]

From what I have read online, if system is low on refrigerant pressure is low and compressor won't kick on.

Good point. My yeah but... Doesn't it kick on for a moment then cycle off?

Second, I would "think" the wire from the dash would how voltage when it is turned on at the dash.

It was running last time I drove it the week prior. But that doesn't mean BOO, your point is taken something to check. Thank you.

Happy 4th

 

[fast 99]

Should have a low pressure switch on drier. Can jump that switch with ac on to check function. If clutch engages either switch is bad or low on refrigerant. If it doesn't engage one side of the switch should have power on it when AC is on. If it doesn't need to trace power loss.

 

[edgephoto]

Before you go crazy guessing and replacing parts you need to know if your system has enough pressure to turn on the compressor. On the accumulator is the pressure switch. It opens at low pressure. Unplug the switch, it has a light green and dark green wires. Take your ohmmeter and see if there is continuity between the terminals. If there isn't your system is low or empty.

If you have continuity, turn your A/C on and see if you have voltage to one of the wires. If you do the issue is the wiring from the switch to the compressor. If you don't then your issue is wiring from the HVAC head. Bad switch, broken wiring, corroded connector. Assuming the fuse is good.

 

[fast 99]

Before you go crazy guessing and replacing parts you need to know if your system has enough pressure to turn on the compressor. On the accumulator is the pressure switch. It opens at low pressure. Unplug the switch, it has a light green and dark green wires. Take your ohmmeter and see if there is continuity between the terminals. If there isn't your system is low or empty.

If you have continuity, turn your A/C on and see if you have voltage to one of the wires. If you do the issue is the wiring from the switch to the compressor. If you don't then your issue is wiring from the HVAC head. Bad switch, broken wiring, corroded connector. Assuming the fuse is good.

Duplicate post

 

[75gmck25]

Do you know what refrigerant you have? R134a is available from any auto parts store, but the older R12 (Freon) is much harder to find.

 

[Edelbrock]

Basically:

Power goes from your battery to the A/C dash switch to the low pressure switch to the high pressure switch to the electromagnet on the pump. If the high pressure switch or low pressure switch are detecting a pressure that's too high or too low, then the switch stops power at that point.

What ever you do, don't bypass those switches by running a power wire directly to the pump (except for testing purposes). If you do, you will either damage the pump by running on low coolant/oil level in the system, or you will cause the system to become over pressured and something will either rupture or the safety valve will blow (if it has a safety).

If the system ruptures, it could quickly fill the cab with an oily "fog", or it could fill the engine compartment with the fog resulting in a fire.

The A/C is supposed to cycle on and off as the pressures in the system change.

If it is low on coolant pressure, then the low pressure switch will prevent the system from ever coming on.


Go to Amazon, and buy a cheap A/C pressure gauge and see where you are at.

Note: You can by pass the dash switch and run a jumper wire full time, but it needs to send power though the pressure switches, to allow those switches to do their jobs. Disabling the switches is like removing the brake system from you vehicle so that it will go faster - yes your car will go faster with less weight, but it wont end well. Same thing for bypassing the switches - yes it will work, but it wont end well.

 

[Grit dog]

Do you know what refrigerant you have? R134a is available from any auto parts store, but the older R12 (Freon) is much harder to find.

Unfortunately it’s not. Several states including Washifornia and the real California have outlawed retail sales of 134a (parts store recharge kits).

 

[gmbellew]

some good advice in the previous posts. a couple clarifications. there is only a low pressure cutoff on the drier. there is no high pressure switch on these old trucks. check for 12v at the low cutoff switch with key on and ac on. if you have 12v there, most likely the system is low on refrigerant. you could jumper the compressor for a second just to see if it works, i guess. but minimally you need a vac and a recharge probably. if you've never worked with the system, it might not be a bad idea to replace the orifice tube and drier first. if you see evidence of black compressor death, then you need a system flush and a new compressor also. but you will know that for sure before you waste time pulling a vacuum and recharging.

 

[edgephoto]

Unfortunately it’s not. Several states including Washifornia and the real California have outlawed retail sales of 134a (parts store recharge kits).

@Grit dog Thankfully I do not live in either of those states. I assume you can buy R134a but you need a license to do so. Is this the case? Just get your EPA 609 certification. Not hard to pass the open book test. Pay the fee and you should be good to go.

From what I read when Googling, you can buy R134a in smaller than 2 lb containers without a 609 cert. The container needs to be CARB rated and you pay a $10 deposit.

 

[75gmck25]

My refrigerant question was not planned to be complicated - the simple question is whether he know what refrigerant and oil is in his A/C. If he does not know, then troubleshooting will start with finding out what he has.

Base on online info, only Washington, California and Vermont have halted R134a sales of the small R134a cans and recharge kits. However, I live in Virginia and I have not gone into a store to check if’s it’s actually on the shelves. Maybe the ban is more widespread.

 

[Broken85]

You can buy all 134a you want on Amazon. Just make sure you are buying refrigerant and not dye for 134a only.

 

[Trucksareforwork]

Everybody has put the good advice out there:

1. Is there enough refrigerant pressure (failure mode: low pressure won’t allow cycling)
2. Are you getting 12v to the low pressure switch (if yes: investigate switch), test by jumping it while running and ac on.
3. If no 12v to switch check fuse
4. If fuse good then you need to check the switch in the dash. It’s what supplies the 12v to the compressor when the switch is in a/c or def mode. I had one burn out a couple years ago.

For what it’s worth: I have blown that fuse by accidentally grounding the idle stop solenoid while trying to adjust idle. I don’t remember why I had the a/c on at the time, but It isn’t hard to do.

And, yes you could simply wire a switch to run your compressor, but only if it goes through the low pressure switch. You’ll burn out your compressor if you run it with low pressure.