A/C compressor won't cycle off?

[87 Pete]

My A/C has been non-functional for the past 5 or so years, so this weekend I added 3 cans of freeze-12 and some oil.

I'm getting 45° temps at the vent outlets, which is lot better than no a/c, however the compressor seems to stay on all the time.

I don't believe there is any air in the system, since there was 15 psi of R12 left in the system, before I added the freeze-12.

I also swapped pressure switches, and no change. Could my system be over/undercharged?

The manual also mentions the orifice-tube being clogged as another potential cause.

My low side pressure is 25-45 psi, high side 130.

Anyone have any ideas?

Pete

 

[scottyb]

Sounds to me like it's pretty good. It may need a little more Freeze-12, look here in the troubleshooting about pressures:
.http://www.gnttype.org/techarea/airconditioning/ac101/ac101.html

Mine will cycle in the morning/mild days, but runs 100% when it's hot out. IMO, constant running compressor is better than a cycling one anyway. Your high side just seems a little low

 

[Rickracer]

More detail needed...

You say your low side is 25-45 psi, but high side is 130? That is pretty low. Are your sure your gauges are accurate? If you are getting 45* temps at the vents, it is probably OK, but high side should be higher.

 

[Red Regal T]

Probably would have been a good idea to change your orifice tube. $2. High side should be around 225-250. Low side around 30.

 

[S10xGN]

My high side pressure is also (low) around 130#. John, you suggest changing the orifice tube. If it was plugged or damaged wouldn't that be a restriction causing the high side to go higher?

 

[Rickracer]

Generally speaking, that is correct

In fact, I have forgotten to install an orifice tube and seen pressures in that range. Unless the orifice is AWOL, it's likely the compressor is on it's way out.

 

[87 Pete]

Re: Generally speaking, that is correct

Originally posted by Rickracer
In fact, I have forgotten to install an orifice tube and seen pressures in that range. Unless the orifice is AWOL, it's likely the compressor is on it's way out.

That wouldn't surprise me if the compressor dies soon. It sounded really horrible when it first started running again,(it hadn't run for at least 5 years) I guess maybe there wasn't much oil in it, but stopped making noises after a minute or so.

It was sweet to have the A/C on today, it's almost 90° here

We'll see how long it lasts...


Pete

 

[scottyb]

BTW, my compressor has been moaning since I bought the car 3 years ago. Still blows cold and it's a daily driver. Your compressor may last longer than you think.

 

[ThikStik]

Not a helpful post here, but could pressures of freeze 12 be the cause? I know its not as radically different as r134 which does require adjusting set points of switch. But it has to be somewhat diff than r12., dont know if that's cause tho.

 

[cwelk87gn]

I know the compressors on ours cars will make lots of noise for a long time before they ever go out. I agree that your pressures are low though. 3 pounds of refrigerant sounds like a bit much, but I know most cars we work on hold around 2 lbs, but thats 134a.

 

[TobyU]

It sounds pretty good to me. I have never use Freeze 12 but I do a lot of ac work.
The low side should be 28-40psi and the high is very dependent on ambient temp.
150-250 is the norm.
The compressor does not need to cycle as long as the evap doesn't freeze up.
If you want it to cycle, there is an adjustment on teh low side switch on the accumulator.
The can you put the refrigerant into.
Take the two wire black rubber connector off and you should see a small screw to adjust cutin/out pressure.
You want the compressor to kick off at about 24 psi. Any lower and you can cause damage to it. You can make it cycle off at whatever you want, like 35psi, but this might raise the outlet temp at the vent inside.
It doesn't need to cylcle as long as the low side is above 22-24 at 1500rpms. I actually feel that excessive cycling shortens the life of the clutch and possibly the comp.
It is easier on the valve and rings in it to stay running than to have to keep starting all the time under a moderate load.
When you first turn the ac on, it is under no load. High side and low side are about 85-100psi. When it cycles, the high side starts to drop from about 200-225 when it is HOT out and wehn it kicks back in it ahs only lowered to about 160-200. This is harder on the compressor than just constanly running.
Good luck.

 

[ThikStik]

Good post. I tried to chince out on my 210k mile 84 Caprice. I set the cycling to more and burned out compressor in 200 miles. Could you find out anything on pressures/capacity of freeze 12. I heard it is now epa controlled. People who have used it say its great.

 

[TobyU]

Freeze 12 says the low side pressures will be 5-10 psi lower than with R-12. I will probably eventually try Freeze 12. SO far I have been able to use R-134a and get by with all the retros I have done. I have ssen a few that just won't get near as cold as with R-12. It has to do with the original cooling capacity or the R-12 system and condensor effeciency etc.
There is a two position orfice tube on the market that lets more go thru at idle so you don't get the typical 10+ degree increase in duct temp when idle in traffic. I have not tried this yet either. I think I will wait until the next one that has a higher duct temp with 134a and then flush and try the Freeze 12 to see if it cools it off more.