Ok, so I'm trying to get A/C back in the car. I have converted the LG4 to a Ramjet, with '727 running things. I got all the A/C parts and lines from my brother's car so I'm trying to work backwards here.

So I guess my question is...there seems to be two switches here, the high pressure switch and a cycling switch. Which is which and is the cycling switch necessary?

 

yes the cycling switch is necessary but which is which... youll have to kill me first hahaha

 

add pics!

 

Ok, you can see what I currently have in the car. Neither the accumulator or the lower line have a switch. I do have the double of each (I have two systems available, parts from my car and my brother's although I don't remember which is from which, but I do have connectors for each thankfully). Anyhow, does this provide any insight?

 

Last pic.

 

Sorry for the rotated pic, I didn't have write access to my main computer from my laptop to flip it. I know, its annoying.

 

Maybe these will help you out. Should show the location of the major components and where they go. If you need more let me know.

 

Last pic is high pressure switch. The one attacked to aluminum line.

 

So the cycling switch is the one in the accum? Then what would be in the compressor, is it a temperature switch?

 

Hmm, heres the compressor.

 

Also, I don't really understand the function of the cycling switch here. Looking at a '91 Y-body schematic, says closes at 41-51psi, opens at 20-28psi...what's the point of that?
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Phatfiddler, the clutch should be the one in the front, but what's in the back?

 

I honestly cant tell you at the moment. If someone doesnt chime in before I get out of class Friday I'll dig out my factory manual and check.

 

Ok, i took some scans of my manual that show the location of the components, and the colors of the wires to match up. Yours may be slightly different, but it should be what you are looking for. The images are large and high resolution so that they are easy to read, so I hosted them on my site. Just click the links below to view them. Feel free to save them to your computer for easier access as well!

Schematic of AC System
List of Component Locations

 

the cycling switch opens so the evaporator doesn't freeze up.
if the evaporator starts to freeze up, you get less air flow across it which will cause it to freeze up even more, which eventually leads to no air flow across it which can damage the evaporator.
some of the cycling switches have a screw between the terminals, you can adjust this screw to raise or lower the point it opens.

the high pressure switch is on the back of my compressor.

 

Thanks to all who replied, and thanks Denn_shah, I do have a switch with a screw in the middle of it, and I have a compressor with a switch which has to then be the high pressure switch, so I think I have all the info I need.

Thanks again
Ben

 

Maybe a little description of function will help.
The cycling switch in the accumulator (big aluminum can) cuts the compressor if the low side pressure drops too low. Like when it is low of freon or the interior fan speed is set too slow to keep the evaporator from freezing up.
The high temp cutout on the compressor cuts the compressor off if the high side pressure gets too high. Like when there is not enough air flow over the condenser (coil in front of radiator) or there is a blockage in the freon system.
That leaves the one in the high pressure (small) line. It turns on the cooling fan (behind radiator) when there is not enough air flow over the condenser to remove the heat.

 

I thought that the fan ran when the A/C was on regardless? Am I wrong about that?

 

Depends on which engine is installed and year model. It's one of the things that they changed up.

 

In my case, I think the ECM ('727re/8D) turns the fan on with A/C input so I guess I can disregard that switch. Thanks.

 

No, you canot "disregard" the low pressure cutoff switch. It needs to be there. If it could be "disregarded", you can be fairly sure the factory wouldn't have spent money on every single car to put it there.

The A/C wiring harness is its own little unit, COMPLETELY separate from the main engine harness, and from the ECM harness. AT MOST, it has a wire coming off of it to tell the ECM that it's running. It is installed into the car along with the A/C system as the car rolls down the production line, separateyl from the other wiring.

The most common-sensical thing to do, if you don't understand how it works (as you evidently don't), is to just go to the boneyard, and gank the whole A/C harness out of a car. It's all by itself, goes through a hole in the firewall behind the right valve cover. One end plugs into the control head, the other end goes to things under the hood. That'll get it back to exactly factory condition, with known good and correct wiring, and all parts working teh way they're intended to.

 

I was talking about the fan switch.

I do understand how it works, I just did not know which switch was which. I like my harness to be as simple as possible, so I build the necessary wires into the same bundle as my ECM harness, so removal is simple and it looks clean. I have all the necessary parts, actually double everything minus the compressor, but its been too long to remember which lines/parts were from which car (one of the lines has a switch, one doesn't; one was from a carbed car and one was from an EFI car). So, if this switch (as stated above, on the smaller line, and in fact the only switch on any of the lines anyhow) is the fan switch, then it's obvious that the factory didn't put one in every car that rolled out of there. Where's the fan control for the one missing this fan switch? Must be with the ECM correct?

The wiring itself is not an issue.

 

Ok, I didn't notice the A/C cooling fan request signal in the schematic, which is controlled by the fan switch, so in my case it is necessary. I've got it now, thanks again everyone.