Question: Where is the A/C low pressure cut off switch?

[coffeejolts]

The A/C on my '81 hasn't worked in a long while. The A/C clutch never engages. So yesterday, I checked the A/C clutch by running a wire from the battery to the positive terminal on the compressor. Bingo- clutch engaged. So now I suspect the switch in the dash, but I'd like to check the pressure switch first before I rip the console and the glove box out.

Where is it located in the '81? The service manual says to check it, but never mentions the location.

 

[Peer81]

On the right side, a metal pipe from your A/C runs down to the dryer, the pipe has a big black rubber connector on it. When you disconnect the connector and short circuit the connector the clutch should also engage. I think you're just to low on freon.

Greetings Peter

 

[coffeejolts]

Thanks! I will check the pressure switch when I get today.

If I short it and the clutch engages, then I either have low freon (and a leak) or a faulty pressure switch. If the clutch does not engage, then it is either wiring or the dash control. Right?

 

[mkapp7879]

To the right center in the pic...
I'd bet you're low on freon.

 

[paz72vette]

There are two differnent sizes pipes. The larger of the two is the low side and is where you chage the A/C from.

If you are low on freon, then you have a leak. Typically oil comes out with the freon. Look for oil spots on the fittings. There are rubber o-rings that tend to leak over time. Also check the condenser. They can pick up rocks.

Also freon is now regulated and requires a certification card to purchase.

 

[coffeejolts]

Update

I jumpered the low pressure switch's connector and the compressor did not engage. Then I checked the voltage through it with my multimeter.

When I have the A/C on, there is less than one volt going through the wires to the compressor. It should be 12+. This sounded like a grounding issue to me, so I double checked that by testing against a known good ground. Still < 1 volt. While I had the meter out, I checked continuity on the low pressure switch itself. It had continuity, so I'm guessing that means that the freon pressure is ok.

I'm left with the console switch as suspect #1.

 

[paz72vette]

Don't think that it is a grounding issue. What you are doing is checking power backwards.

Do you have power at the fuse? Do you have power at the switch?

Where I live we have a corrosion problem and wires corrode. If you have power at the switch, check the wire with your volt meter at both ends. This is typicle in high humid area. I have replace more wires then components.

Do you have a schematic that you can forward to me?

Cheers

Vito