A/C High Side Low Pressure Switch - does it exist?

[vangremlin]

I'm getting the A/C going on my 1980 coupe (Ginger).  Most A/C systems have a high side low pressure switch, to keep the compressor from running when the pressure is low.  For the life of me, I can't find one on this car, and from looking at the TSM, there never was one.  This kind of confirms how the car operated when there was no refrigerant in the system - the clutch would still engage and the compressor would run.  The TSM shows that there was one built into the compressors on 1980 4 cyl (non-Eagle) cars.  But nothing mentioned for six cylinder cars, and nothing in the wiring diagram.  RockAuto lists one for Eagles in 1980 and 1984, but that could have been associated with dealer installed units.  Anybody got an answer on this one?  Thanks.

[BenM]

It was a 4cyl only option in '80. The 151 used a different compressor, not a Sanden or York.

I would infer that if you were changing to a Sanden compressor you'd need the low pressure switch, but it isn't necessary for the York. I expect because the York is internally lubricated and the other two compressors rely on oil in the refrigerant to operate properly.

If it exists, it'll screw into the sight glass.

I don't know about the American Air (dealer) systems, but I think someone here has one.

[Amc1320]

Is this the high pressure switch? I had to replace this one as one of the tabs broke off

AC is not my specialty.....

[vangremlin]

That sure looks like it!  Is that on your 84 wagon?  Thanks.

[Amc1320]

Yes on the 84 wagon, it was broken like I said and I had to run a jumper wire across the plug to get the AC to work, when I pulled the engine since I lost all my freon anyway I went ahead and replaced it,

[Amc1320]

By the way I pulled the replacement one off my 83 spirit parts car, also with a six cylinder

As Ben points out I have a Sanden compressor,, my dad's 79 concord has a York and does not have this switch

[rollguy]

If your car has the wiring for the switch, it would not be a big deal to add one.  However, no stock wiring and you would need to add the wiring, and that would be complicated. 

[vangremlin]

If your car has the wiring for the switch, it would not be a big deal to add one.  However, no stock wiring and you would need to add the wiring, and that would be complicated.

As I understand things, the switch is to shut off power to the compressor when the pressure is low.  I've read that the switch is closed under normal conditions, then opens when the pressure drops below a certain point.  Wouldn't I just wire this switch in line with the wire going to the A/C clutch? So that the wire that went to the clutch now goes to one terminal on this switch, and then run a wire from the other terminal to the A/C clutch?  I'm pretty sure the switch doesn't interrupt the ground feed to the compressor as its grounded by being bolted to the mounting bracket.  Thanks.

[vangremlin]

By the way I pulled the replacement one off my 83 spirit parts car, also with a six cylinder

As Ben points out I have a Sanden compressor,, my dad's 79 concord has a York and does not have this switch

Is the piece with the sight glass a separate piece of hard line, that goes between the receiver/drier and the high pressure hose that leads to the evaporator?  I think the car I pulled the Sanden compressor from is still in the junkyard, hopefully I can grab it from that car.

[rollguy]

If your car has the wiring for the switch, it would not be a big deal to add one.  However, no stock wiring and you would need to add the wiring, and that would be complicated.

As I understand things, the switch is to shut off power to the compressor when the pressure is low.  I've read that the switch is closed under normal conditions, then opens when the pressure drops below a certain point.  Wouldn't I just wire this switch in line with the wire going to the A/C clutch? So that the wire that went to the clutch now goes to one terminal on this switch, and then run a wire from the other terminal to the A/C clutch?  I'm pretty sure the switch doesn't interrupt the ground feed to the compressor as its grounded by being bolted to the mounting bracket.  Thanks.

Actually, the switch is normally open (no pressure).  When the system is charged, the switch closes so the clutch can engage when energized by the A/C controls (or defrost).

[vangremlin]

Actually, the switch is normally open (no pressure).  When the system is charged, the switch closes so the clutch can engage when energized by the A/C controls (or defrost).

Thanks!  Sounds like we're saying the same thing - no pressure, switch is open.  Pressure, switch is closed and clutch can engage.

[BenM]

By the way I pulled the replacement one off my 83 spirit parts car, also with a six cylinder

As Ben points out I have a Sanden compressor,, my dad's 79 concord has a York and does not have this switch

Is the piece with the sight glass a separate piece of hard line, that goes between the receiver/drier and the high pressure hose that leads to the evaporator?  I think the car I pulled the Sanden compressor from is still in the junkyard, hopefully I can grab it from that car.

That's it.

They come in overpressure and over-under combos as well. You can just wire it in the feed for the clutch, that's how the wiring diagram has it.

[rollguy]

Actually, the switch is normally open (no pressure).  When the system is charged, the switch closes so the clutch can engage when energized by the A/C controls (or defrost).

Thanks!  Sounds like we're saying the same thing - no pressure, switch is open.  Pressure, switch is closed and clutch can engage.

Going back and reading it again, you are correct.  However, I  confused the term "normal conditions" with "normally open", which is what the switch would be in it's natural state (without pressure).

[vangremlin]

That's it.

They come in overpressure and over-under combos as well. You can just wire it in the feed for the clutch, that's how the wiring diagram has it.

Thanks!  Gotta work in a trip to the junkyard this weekend!

[vangremlin]

Going back and reading it again, you are correct.  However, I  confused the term "normal conditions" with "normally open", which is what the switch would be in it's natural state (without pressure).

Cool.  I think I'm finally getting things straight in my head.  Thanks to everybody for your input, I am going to be so cool this summer - well, at least when I'm driving in my coupe!