A/C and vacuum

Rob Benham · #1 (**permalink**) 06-30-06, 05:44 PM

I hope it's okay to put this on this forum as well, cos I have found this good for my SLS and the technicals are probably the same.

My (almost) perfect 95 Fleetwood Brm's A/C failed today. The compressor is not running at all, and the pressure on the low side was way round into the red.

I had topped it up a few weeks ago and it was fine. When it failed, it was again okay for a few mins, then failed again. It did this a few times.

A clue. The park brake does not always come off...er, so to speak...and I wondered if it was a lack of vacuum failing to acctuate the louvers etc. But, this may be a red-herring, so any ideas are welcome. Rob

**Ranger** · #2 (**permalink**) 06-30-06, 06:21 PM

If you loose vacuum to the cabin, the HVAC system will default to defrost. Compressor not running indicates low freon.

Rob Benham · #3 (**permalink**) 07-01-06, 03:20 AM

Thanks for that. I guess that the standing temp indication of 117f may have made things more difficult for the system. (the real outside air was 95.f)

Certainly the air coming out of the vents was hotter than when switched to ECON. I seem to remember that defrost heats pre-cooled air...so if it wasn't being cooled it would be heated, right?

I'm not sure what caused the very high 'low line' pressure to be so high though.

ewill3rd · #4 (**permalink**) 07-01-06, 08:55 AM

I am pretty confused, but I'll try to answer.

If the vacuum control system is not working for the a/c then air distribution will not work. The air will default to the defroster duct.
The other poster was right, the air should still be cold if the A/C system is working because the temperature door is usually mechanically controlled and will have little to do with vacuum. If it's still warm or hot you could have lots of problems.
You must be sure that the compressor is being deactivated because of low refrigerant. It could be a failing compressor clutch coil or a faulty programmer or even wiring problems.
Simply adding refrigerant could cause a massive overcharge, which would also make the compressor shut off and poor system performance.
There are too many variables here for us to give you good diagnostic information based on what you have posted so far.
I would strongly recommend taking the car to a trained/certified professional for proper diagnosis.

Usually the vacuum release on the park brake is a failing actuator on top of the pedal on the older ones. They are serviceable.

Hope this leads you to success on your a/c quest.
Good luck.

zonie77 · #5 (**permalink**) 07-01-06, 11:43 AM

An idle pressure (compressor not running) of 150 may still be below full. I've looked at the last couple I had to top off.

120 definitely needed freon, 150 just needed a small amount. Running pressure dropped to 30 low side. This was at 95F.

If the compressor is not running the gauge on the can means nothing.

Rob Benham · #6 (**permalink**) 07-01-06, 11:44 PM

Right! that's what i wondered. Low charge....hot day....very hight 'low' pressure.

When we got this car it was up to date on servicing, but after 300 miles the A.C seemed weak. Topping it up seemed to help, but it was still just cool air, not freeeeezing.

Anyway, today i put some more Advance Autoparts 134a in, and after a looooooooong time, the compressor kicked in for a moment. After a full ten mins, the compressor was on for 90% of the thime. Prior to this, on two other cars, the same kit filled the system quite quickely. Now I wait with baited breath to see if the pressure falls off again.

It does sound as though there are other issues with the overall system.

Rob Benham · #7 (**permalink**) 07-01-06, 11:44 PM

This is a new one!!!!!!!!!!!!!! TEN coppies of a post.

EDIT Seems that they have gone away.

**Ranger** · #8 (**permalink**) 07-02-06, 11:53 AM

Quote:

Originally Posted by Rob Benham

Right! that's what i wondered. Low charge....hot day....very hight 'low' pressure.

When we got this car it was up to date on servicing, but after 300 miles the A.C seemed weak. Topping it up seemed to help, but it was still just cool air, not freeeeezing.

Anyway, today i put some more Advance Autoparts 134a in, and after a looooooooong time, the compressor kicked in for a moment. After a full ten mins, the compressor was on for 90% of the thime. Prior to this, on two other cars, the same kit filled the system quite quickely. Now I wait with baited breath to see if the pressure falls off again.

It does sound as though there are other issues with the overall system.

Compressor cycle times will vary, depending on ambient tempurature and humidity. 90% might be normal for Texas from what I expirienced when I was there last week (97 degrees).

zonie77 · #9 (**permalink**) 07-02-06, 01:40 PM

Quote:

Originally Posted by Rob Benham

Right! that's what i wondered. Low charge....hot day....very hight 'low' pressure.

That is not what I said. Compressor NOT running gives you a meaningless pressure reading. You are reading a static pressure in the system. Reading the high and low sides with it not running will give you the same exact pressure. When the compressor starts it sucks it from one side and forces it into the other side with a small orifice between them, that gives you different pressures on either side.

zonie77 · #10 (**permalink**) 07-02-06, 01:42 PM

Look at this site.

http://www.autoacrepairs.com/gauge_r..._diagnosis.htm