1982 300D, A/C electrical issues

[Jon Andrews]

First of all, thanks to everyone who makes this forum such a great resource. I've been referring to the forum frequently over the last year, and I'd be lost without it. This is my first post.

I recently had a very competent Volvo indy install a new compressor, receiver-drier and expansion valve in my 1982 300D, and charge it up with r134 (it had been converted by the PO). Everything went fine, but he couldn't get the system going because the high-pressure switch wasn't getting any power. The fuse was fine.

Anyone out there had a similar problem? I know, from my research on this forum, that the '82s don't have a Klima relay--so do they have some precursor ice-cube style relay or nothing at all? Is there anything between the fuse and the high-pressure switch that I can replace or fix? I don't have a good electrical diagram for the car, so I'm at a bit of a loss, and will be grateful for any advice offered.

Thanks in advance for your help.

-Jon

1982 300D

[tangofox007]

Originally Posted by Jon Andrews

Is there anything between the fuse and the high-pressure switch that I can replace or fix?

The low pressure cut-out switch (and then the compressor clutch) is powered by fuse F8 through the compressor relay. The compressor relay (actuation side) is powered through the CCU pin C1 and the evaporator temp regulator.

[Jon Andrews]

Thanks for the help, tangofox007. Where is the compressor relay located? Is it one of the ice cubes on the fender, or is it under the dash? If you have time, can you please explain how the system works? What information is required by the relay before it sends the current through to the low-pressure switch?

Thanks again for your help. It's 95 and muggy as heck here in VT.

-Jon

[getstevenow]

Have a similar problem with my 87 300D.

Again this forum is invaluable and thank you for those of you who post your expertise and share your knowledge.

Converted over about a year ago and then indy guy couldnt get it to work all the time. The AC doesnt work if the tach doesnt register.

How best can this be fixed?

Thanks in advance for your help

[tangofox007]

Originally Posted by Jon Andrews

Where is the compressor relay located? Is it one of the ice cubes on the fender, or is it under the dash?

It is on the left fender. The front cube is the compressor relay, the rear one is the aux fan relay.

Originally Posted by Jon Andrews

If you have time, can you please explain how the system works? What information is required by the relay before it sends the current through to the low-pressure switch?

The compressor relay receives power from the push button unit wnen an a/c mode is selected. Power is routed through the evaporator temp switch, which is closed above 36-40*F (opens below that temp range to prevent the evaporator from freezing.) The relay is actuated, routing power to the compressor clutch through the low pressure cut-out switch on the receiver/drier. The cut-out switch opens below 10 psi to prevent compressor damage due to low refrigerant.