1978 AC Temperature Cutout Switch

[curtis]

I'm no expert, but pressure readings should be taken with the unit running and the system stabilized. So let it run for a good ten minutes then get readings. It is normal to have higher presssure on the low side with system off than with it running. this is because the total charge equalizes when off and when you start it up, more freon is on the high side of the compressor causing the low side to stabilize lower than when it is off.

 

[1978L48jafo]

Thanks Curtis, found a couple how to sites on charging 134 they agree with your comments. Real cool in the vet now, but I am feeling like a duh..... and I am still a little low 25 psi and 54f at the vent, much better, summer drives are looking up........:cool
John

I'm no expert, but pressure readings should be taken with the unit running and the system stabilized. So let it run for a good ten minutes then get readings. It is normal to have higher presssure on the low side with system off than with it running. this is because the total charge equalizes when off and when you start it up, more freon is on the high side of the compressor causing the low side to stabilize lower than when it is off.

 

[Ludigdrums]

Ooh, Me Too: Another Questions for the AC Experts

My '81 air blows cold and seems to work perfectly, except the compressor does not cycle. I'm guessing this is the reason that when I got the car, the electrical connection to the compressor was not attached.

I have suspicion about the pressure switch, which I understand is adjustable. How do I go about testing/adjusting this? I would assume I need a set of guages.

Now, I know that there are different amounts of time and such that compressors cycle at...but again, mine never does. I try not to run it too long because I'm afraid of doing damage to an otherwise OK system.

Any thoughts? Thanks!

- Jeremy

 

[brusso]

Question for the AC experts. Should the low pressure side reading be taken while the compressor is idling or running? My low side pressure right now is above 50 with the compressor is not running and then drops to about 25 or slightly lower when it kicks in. Working pretty well right now but I don't want to leave in a overcharged condition.

That's about right. It should read about 28-30 while compressor running, on the low (blue) gauge. On the high side, it should read about twice the ambient air temp. For example, if it is 75 deg ferinhiet, the high side should read about 150 psi.

If your getting 25 or lower, while running compressor, you may be a little low on freon. Unless the high side is reading too high. If the high side is too high, you may have a restriction in system.

 

[1978L48jafo]

Thanks Brusso, I only have the low pressure guage at the moment. I am sure there are no restrictions in the system I checked everything during the rebuild. I will go ahead and add another can. Thanks for the thumb rule on the guages ad ambient pressures, I have my eye on a set and I seem to have been having a rash of AC problems over the last few years.
John

That's about right. It should read about 28-30 while compressor running, on the low (blue) gauge. On the high side, it should read about twice the ambient air temp. For example, if it is 75 deg ferinhiet, the high side should read about 150 psi.

If your getting 25 or lower, while running compressor, you may be a little low on freon. Unless the high side is reading too high. If the high side is too high, you may have a restriction in system.

 

[1978L48jafo]

Jeremy,
You may want to start a thread with your problem in it. I am far from an AC expert just read back through my post.....;-) If your air won't cycle with the load I would check the cut out switch located on the tube going to the bottom of the cooling coils. I am told that is shuts off the compressor (disengages the clutch) when tempeture is around 34 degrees. To check it put a multimeter across the pins and turn on the ac. my original go moved too many times and the tube was cracked allowing the gass to leak out. Post your question in a seperate thread someone will help.
Regards
John

My '81 air blows cold and seems to work perfectly, except the compressor does not cycle. I'm guessing this is the reason that when I got the car, the electrical connection to the compressor was not attached.

I have suspicion about the pressure switch, which I understand is adjustable. How do I go about testing/adjusting this? I would assume I need a set of guages.

Now, I know that there are different amounts of time and such that compressors cycle at...but again, mine never does. I try not to run it too long because I'm afraid of doing damage to an otherwise OK system.

Any thoughts? Thanks!

- Jeremy