pleasants9

I Just charged my a/c system and I think the pressure switch/ clutch cycle switch is bad? The compressor will kick on then kick right back off again and it just keeps doing this, if i bypass the switch and just bridge the two terminals of the boot that plugs into the switch, the compressor turns on and off just fine with the a/c controls in the car. Does this confirm the switch is bad? and if it is should I replace with the OEM switch? I have since swapped my system from r12-r134a. I replace the compressor, orifice tube, and accumulator when i did it but not the switch.

'75

Sounds more like a low charge.

redcruz1120

I agree..

mark79,80

I would hook up a set of manifold pressure gauges to the system and monitor the pressures when the compressor cycles off. If the low side drops much below 30psi the compressor will cycle off. If so the system is low on freon. You can compare the low and high side pressures against the readings on a pressure chart to see if they are in spec.

Dynra Rockets

Hook up a gauge and see what it is reading. 134a in a R12 system will run higher pressures. In another R12 car I have the compressor would cycle on/off a lot due to exceeding the safety switch limit when I ran all 134a. I now run a blend of propane/134a and keep it underfilled slightly and have no more issues.

https://www.corvetteforum.com/forums...my-1969-a.html

R

Street Rat

The switch is different for R134a versus R12.

pleasants9

OK so when i plugged in the low pressure gauge it was initially sitting at 80 psi.

I bypassed the switch and engaged the compressor. Pressure dropped and settled at 6 psi. I ran it for 3 minutes and it stayed steadied at 6 psi, so it looks like my system is low?

Then when I turned the compressor off, the temperature rose and settled at 49 psi.

pleasants9

update: Went ahead and added another pound. Got the low side pressure up to 30 psi and holding. The compressor now cuts off when i raise the rpms up to about 2000rpm the pressure drops down to 20psi and the compressor cuts out. Wondering if I should add about another 1/2 pound.

redcruz1120

I would check the recommended amount the system holds first.. I have that info at home, but wont be home anytime soon.

pleasants9

it holds 3lb 8 ounces total i believe, but i don't know how much was left in there before i started trying to fix the problem of the compressor not coming on at all.

Wrecked82

I think this would be a fairly fast diagnosis and fix, if low pressure, from a good shop. Know when I converted to 134, a quality shop did it, which did include a new switch (not the connector - see my other post elsewhere). This has now been at least three years and still do not need a charge. Did include a new compressor that has died. Its 80*already today in Houston and a/c is ice cold.

JPinAZ

This time of year fill it to low side 35psi idle, high side 200. Should be good to go with r12 or 134. Starting point for r134 is 75% of r12 spec.

JPinAZ

Sounds correct to me

BLUE1972

lvmyvt76

John Vance

hi there was reading the a/c comments and was wondering how would I tell which freon is in my 79 vette. There’s no labels and I bought the car used. Any help would be great thanks

interpon

Pics of fittings may help if converted..if not hard to know
maybe start a new thread..

derekderek

this is an adjustable r12 low pressure switch. it is an r12 switch but can be turned down. 134 likes lower low side than 12. https://www.ebay.com/itm/181723260861