How does the AC system work in early OBS models?

[PlayingWithTBI]

I've been searching for answers on how the AC system works in my 88 C1500 Silverado. Some places I read newer models that have the "re-circulation" button will open the door by the blower motor to get more cab air (when the AC is turned on), however FWIU the earlier models, like mine, by turning the blower on high, it will open that door. Somewhere I read the high pressure switch on the back of the AC compressor opens this door.

What I can't find is a schematic of the wiring that includes this HP switch to the ECM or the climate control system. Monday, I'm going to replace my compressor, orifice tube, and the HP switch because that switch blew out of the compressor and I'm afraid the snap ring groove is too shallow to hold up again against whatever pressure the old compressor was developing.

I'm going to try some tests like shorting out the switch and see if the door opens. I know from the last time we installed the existing compressor that switch wouldn't do anything to effect it running or not. The low side switch on the dryer/accumulator would shut it off when disconnected.

I'm thinking of hooking the HP switch in series with the LP switch and shorting out the HP connector to allow the fresh air door function. Any ideas/hints as to how it's supposed to work or if my idea will work? Anyone have a schematic for the 88 climate control?

This is all I could find for the AC to ECU wiring; note it only shows 1 pressure cycling switch in the circuit.

I don't want to waste another $240+ on compressors, oil, orifice tubes, and Freon...

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Hope this makes sense, I'm on my 3rd Ta-Kill-Ya

 

[andy396]

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[andy396]

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[andy396]

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[andy396]

Happy reading [emoji846]

 

[PlayingWithTBI]

Thanks Andy, lots of good stuff.

Where I'm concerned is on page 65.0, the air inlet valve pressure switch. I'm thinking this valve is on the back of the AC compressor. Which means, There is NO system high pressure shut off. All this valve does is actuate the fresh air door.

I hate to ask but, can you get a better picture of that page?

 

[studigggs]

You are correct. There is no high pressure cut-off switch on models w/o the recirc/fresh button on the control head. The high pressure switch on the back of the compressor is the Air Inlet Valve Pressure Switch. If you dont transfer the swicth to your new compressor, you can just ground the connector and then your system will work as if the switch is closed all the time (recirc enabled after 30s on Hi/Med, full cold)

 

[PlayingWithTBI]

Well then, do you see a problem with wiring this HP switch (I have one that's on @200- & off @ 450psi+) in series with the LP switch at the receiver? Then I'll ground out the OE connector at the compressor to the T-stat housing.

 

[wheelman]

Do the deal right. Don't rigg anything up. You will be causing problems. Replace it all like you see it. Switch on the back of that compressor. Replace it with a new one. I did mind while back. Got the parts rockauto. I replaced everything with new. Front to firewall. Condenser to dryer. All lines and switches. New oil and freon.

 

[Jglew82]

Well then, do you see a problem with wiring this HP switch (I have one that's on @200- & off @ 450psi+) in series with the LP switch at the receiver? Then I'll ground out the OE connector at the compressor to the T-stat housing.

You might wanna double check the HP switch if you go this route. If it doesn't close until 200psi, your compressor clutch will not engage because your high side static pressure will equal roughly the ambient temp when the ac is off.

I like the general idea of this, though. From A/C "on" switch >LP switch>HP switch>compressor clutch. That way, either of the switches has final say in the clutch operation.