A/C issue

[Rick Biarritz]

Came home on FRI, A/C was blowing barely cool, was drenched in sweat when got out of the car.

Running it in the driveway right now, it SEEMED pretty cool, but I couldn't really say without taking a trip.

Hooked up the hose that comes with a can of coolant.

When the compressor CUTS OFF, the pressure jumps up to where it belongs (55-65 psi).
With the compressor running, the PSI drops real low.
Is this normal? The can of coolant doesn't say if the pressure is supposed to jump as the compressor turns on and off.
Lastly, the compressor runs for about FOUR seconds, cuts off for FOUR seconds, comes on for FOUR seconds, etc.
I suspect that this is NOT normal. Yes/no?

Thanks

["Cadillac Kid" Greg Surfas 15364]

Rick,
I don't know what year you are working on, or what refrigerant you have in the system, but it sounds like the compressor is "short cycling" which is most likely caused by a shortage of refrigerant , bad expansion valve,  a plugged dryer (in order of most to least likely), or a restriction in the liquid or suction lines.
Greg Surfas

[Rick Biarritz]

83 Eldo that HAS been upgraded to the new stuff.

Thanks!

[TJ Hopland]

'Real low' on the low side is usually a sign of low refrigerant.   It would be best to get a dual gauge set and see what the high is doing at the same time before adding anything to it.   

When the conversion was done did the compressor get swapped out?   How about hoses?   If the hoses didnt get done it would be somewhat normal for R134a to leak a bit over time because is molecules are a bit smaller than the R12 the stuff was designed for.   If the compressor did not get changed there would usually be the old oil still in it.  The rest of the system is fairly easy to flush the old oil out.   The new and old oil when mixed tends to turn to goo over time which does not do various places in the system or the compressor any good.  This could mean the orifice tube is now plugged with oil goo or that the compressor is coming apart and its plugged with compressor bits.  This is where the dual gauge comes in.  A blockage in the system would cause the high side to spike up high, possibly tripping the high pressure cut out switch, and because its not flowing this would also cause the low side to go very low which may also drop the low pressure switch.  After a little pressure gets through the blockage things get more back to normal till the compressor kicks in again and the whole process starts over again.  Adding refrigerant in this situation would only make things worse. 

Im not sure where they put the tube in that vintage Eldo.   My guess is its going into the evaporator at the firewall.  Im not 100% on that, sometimes GM put it up at the condenser too.   I will likely find out soon when I try to get it working in my 80.  Im just waiting for a new fuel pump.  Changing the pump is easier with the AC out of the way not to mention cant run the engine with fuel squirting all over the place like it is now. 

One thing I learned about why the converted systems and early 134a systems just did not work that good especially at low speeds and idle is in the mid 90's most went to a variable displacement compressor.         

[76eldo]

Rick,

There is a balance point between the high side and the low side of the system.  If the compressor comes on at all that means it is holding a charge, but may have a slow leak.  Adding more 134-a and working without gauges, you may luck out if you add a can and check the inside temp, but there's a lot more to the Climate Control system than just having enough freon in it.

Might need some professional help with the AC.

Brian

["Cadillac Kid" Greg Surfas 15364]

Rick,
With an R-12 system that has had its refrigerant replaced with R-134a, all bets are off regarding possible problems.  Depending, as TJ says on the quality of the "clean up" to eliminate the Mineral Oil the system originally contained, any possible modifications to the system and again the quality of the workmanship doing the job which should have included replacement of all the "O rings" (combination of R-134 and compatible oils is erosive for the rings used in R-12), checking of all hoses for leaks, etc., checking the compressor shaft seal ( the site of probably 80% of refrigerant leaks due to the non use of the system and they drying out of the seal during off seasons).
Rick, working on refrigerant systems (of all kinds) is a specialty, and is a task that requires specific expertise.  My suggestion is that you take it back to where you had the R-12 replaced, and at least get a diagnosis. 
Greg Surfas

[Gene Beaird]

Rick,  yes, that is to be expected.  When everything is working well, and the system has a full freon charge, the drop is still there, just not as obvious.  Your system is short-cycling.  The single-hose charging kits will only hook to the low side, that's to prevent someone from trying to fill the high side, and potentially blow up the refrigerant can.  The compressor comes on, and pulls the low side down to the point the low pressure switch cuts compressor clutch power.  The pressure equalizes, and the switch re-energizes the clutch, and away you go, until the pressure drops below the value set on the low pressure switch. 

You probably just have a small leak somewhere.  If it has been several years since the system was converted, then it could be just normal seepage.  If it's only been a year, or two since the conversion, your leak may be more of a problem.  As others have recommended, you may want to take the car back to the place that did the conversion (if that's possible), and have them inspect it for a leak.  They can be annoying.  There's not much worse than being uncomfortable in a Cadillac.