1991 Trans AM AC system in my 1985 Camaro TPI. Charged with R12a.

Seems to make sufficiently cool air but the compressor clutch never cycles. It stays on 100% of the time whether the engine is at idle or driving around.

Also recently the compressor/clutch has started making a faint squeaking noise when engaged. It is silent when the clutch is not engaged.

 

Cycle Switch might be bad

AC Delco 15-2151 GM Original Equipment Air Conditioning Clutch Cycling Switch
Part Number: 15-2151

 

Can the switch be changed without loosing the system charge?

 

YES. It has a small poppet in the stem. you'll get a real quick "pfffft", that's it.

 

I took the switch and put it on my 92 S10. It worked fine. So i put it back on the Camaro and turned in the screw between the terminals a few turns. It is now cycling on and off.

But at what pressures and how frequently should the clutch cycle? Im sure it varies due to ambient temperature. I have a low side ac gauge.

 

If it cycles too much, you'll never get the full cooling due to the cycling. On the other hand,if it doesn't cycle, you can freeze up the coil. Read this thread/post.

https://www.thirdgen.org/forums/cool...tem-134-a.html

 

R-134 low side pressure is around 35psi at 90*

 

Hey guys, I need to hijack this thread.

I have replaced my whole A/C System. Following parts are new:
- A/C Compressor (ACDelco)
- Hose package from Compressor to Condenser / Dryer (Four Seasons)
- Condenser (Spectra Premium)
- Dryer (ACDelco)
- Orifice (ACDelco)
- Evaporator (Spectra Premium)
- High Pressure Cutout Switch, located in Compressor Head (ACDelco)
- High Pressure Switch, located in the discharge line between Condenser and Evaporator (Four Seasons)
- Low Pressure Cycling Switch, located in the Dryer (Four Seasons, for R134a)

A/C works and cools, but my clutch also won't disengage. Air outlet from the vents is 16°C / 60°F, standing vehicle, outside Temp. about 30°C / 90°F.
But the clutch never disengages. I'v tried WOT, then it disengages how it should. Also it disengages when Economy Modes on Switch Pod is set. It disengages, when I pull the conncetor at the Pressure Cycling Switch.
For a first test, I unscrewed the R134a Pressure Cycling Switch and screwed on my old R12 Cycling Switch. Same problem.
I don't have manual pressure gauges at home. Maybe tomorrow I can borrow one for the low side from a friend.

I have bought all parts at RockAuto. Here is the tecnical info for my new R134a Switch: http://www.rockauto.com/catalog/more...nid=457&jpid=3

And this is the info for my old R12 Switch: http://www.rockauto.com/catalog/more...nid=457&jpid=1

I am no expert in A/C Systems, why will the clutch not disengage? Can there be another reason?

Thank you!

Oli

 

Looks to me, by the discharge temp, like it's over-charged.

There's no law that says it "has to" cycle. In fact, most cars usually won't, especially sitting still, if the temp is much over about 80°F (27°C or so).

If you put in R-134A but used the correct orifice tube for the original car, as in, if you looked it up in the parts books for 92 Firebird and used that, then that's another reason it doesn't work like you would expect. The Frod orange one works ALOT better in a GM R-12 system filled with 134A, than the GM one does when used in the same mismatch conditions. Next time you have it apart, replace that; get the one for about a 96 Crown Victoria.

The low pressure shutoff switch shouldn't matter all that much. Operating pressure at that point in the system isn't all that much different between the 2 refrigerants.

 

Over-charged...
The little sticker on my blower module told me, the amount of R12 ist 1,02 kg. I've read serveral times, that if you are retrofitting to R134a, you need to charge 90% of the original R12 amount. So I've charged the system with 900 gr R134a. Is that to much?

And yes, I've ordered the original orifice tube for my 92 Bird. Which one from the Crown Victoria should I choose? (Don't worry about the german lanuage )
http://img5.fotos-hochladen.net/uploads/1lwu1p7j4sa.jpg

I need to order some other parts at RockAuto next week, I will order the other orifice tube with them and replace it asap.

Oli

 

Well:

Yup.

 

Thats remarkable... How much should I charge? 800 gramm? 850?

 

Hard to say; aim for the amount that brings the discharge air to around 45° under those conditions. No idea what weight that will turn out to be. Should then be near 35° at cruising, and should cycle at cruise if the ambient temp is around 75° or below, ideally with the discharge air as close to freezing as possible without icing up the evaporator. (all in °F, sorry) The object of the exercise is, adjust the charge until it matches whatever the combination of parts you have, works the best. Not really something you can look up in a "book" especially since your car no longer matches ANY "book". Rather like ignition timing, carb jets, etc. ... find what YOUR car works the best with, given the combination of parts YOU have RIGHT NOW, the way YOU want it to work for what's important to YOU the way YOU drive it where YOU are etc. etc. etc. We call that "tuning". It applies to most of a car's subsystems. If I knew some exact "spec" I'd be glad to give it to you, but TUNING doesn't really work that way.

 

I've done a little research and found a good "formula" I guess for charging the system:

R-12 amount x 90% – 1/4 lb. = R-134a amount

I think I just forgot the "- 1/4 lb." part... 1020 gramm - 10% = 918 gramm - 1/4 lb. = 804 gramm.
I think I will charge 810 gramm and then check the cycling again.

Thank you all!

EDIT: Charged the system with 810 gramm yesterday... And still no cycling and the outlet temp ist the same... This sh%& drives me crazy.