Looking for some A/C troubleshooting tips

[notny41]

My '86 951 A/C compressor does not turn on - a free local a/c inspection technician told me that there is pressure in the lines but the compressor is not engaging. I would imagine it is a pressure switch preventing it from engaging. I'm just not sure which switch is the one that tells the compressor that there is pressure in the system. Can someone help me with the location and possibly a picture of where to find this switch so I can try shorting the connectors to see if the compressor will engage after doing so?

[Tom]

The pressure switch is the green thing on the receiver-drier, in the driver-side headlight bucket. This pic shows it from the top with the receiver-drier siting to the right. Not sure if there is a connector nearby for easy jumping. You can also hotwire the a/c clutch but disconnecting its spade connector and giving it 12 volts positive straight from the battery (with in-line fuse if you're not feeling lucky). You might start by just removing a cap and pushing on the Schrader valve to see if there is any meaningful pressure in there. Should be like letting air out of a full tire, just messier. Wear gloves and goggles.

acpressure switch.jpg (609.94 KiB) Viewed 1128 times

[Evan]

The low-pressure switch is on the accumulator black cylindrical tank near the firewall. It's a two-wire connector. Unplug it and jump the two terminals in the connector with a paperclip or wire. If the compressor clutch engages, the system is low on refrigerant.

[Tom]

The low-pressure switch is on the accumulator black cylindrical tank near the firewall. It's a two-wire connector. Unplug it and jump the two terminals in the connector with a paperclip or wire. If the compressor clutch engages, the system is low on refrigerant.

On an '86 turbo? The pic I posted was from my own '86 turbo.

[notny41]

does that green connector just pull straight off? And I would assume that is the one I would need to short between the two terminals on the green part right?

I also have what looks like another pressure switch down there too as indicated by the arrow. Does anyone know what that would be for?

IMG_0095.jpeg (511.12 KiB) Viewed 1114 times

[Petethepug]

You’ve got to take to a shop for a proper diagnosis. Pay yourself forward. If you accept the lure of “just needs a XYZ” and you let the shop loose on it that says it services Honda, Ferrari, Kia, Jaguar, etc, there will be regrets.

How long has the system been inoperable? Is it still r12? If you’ve got a budget, get the estimate. It’s a simple system by today’s standards. Don’t let an amateur buggar it up. $150 an hour to a pro is less than $80 an hour to an amateur.

[Tom]

Good point, sorry for the confusing post above. The green one I believe is the high pressure switch, and the one you point to is the low pressure switch. The few times I have had to jumpstart the air conditioner, I just use the spade connector on the compressor itself as I mentioned above, so I would need to dig in a little to confirm that, but pretty sure. I bet @gb951 can confirm. I think the connectors do just pull off the low pressure switch with spade connectors. So if you suspect low pressure, that may be easy to jump...

[gb951]

I have pulled the spade connectors off that switch in the past and have used a jumper to cycle the compressor.

[Petethepug]

I had to google “when should admin/mod apologize for another members post if it seems confusing?”

[Tom]

I had to google “when should admin/mod apologize for another members post if it seems confusing?”

No, no, I was referring to my own post because I pointed to the green high-pressure switch instead of the low pressure switch below it.