Need some advice folks. I've been working with a (national chain) shop on an AC conversion from R12 to 134a. I've installed a remanufactured compressor, accumulator, orifice tube, all new o-rings and utilized 6oz of Castrol Retro-fit ester oil. System evacuated successfully and held vaccum. The problem, when charging with approx. 2.75LBS of 134a, both low side and high side pressures way too high. Compressor also making a knocking sound when clutch engages. Shop says the compressor is bad. Does that sound right? Could there have been too much oil (4 oz)poured into the compressor when we installed? Is there a 134a activation switch that I should change? Haven't done that. Open for ideas before I drop another $250 on a remanufactured compressor or should I bite the bullet and get a new Delphi compressor.

 

What year car and what type compressor?

Did you flush the system (evaporator, condenser and all lines)?

Did you spin the compressor by hand prior to starting the engine and engaging the clutch?

Did you add oil to the other components (accumulator, condenser, evaporator)?

Neal

 

Might take a few remanufactured compressors before you get a good one. Sign of the times

 

i went throught he same situation, 2 rebuilts , and ended up buying a new compressor,
been cooling great now for over a year. you may want to change to a sanden 508, with accomp. brackets.
that will be my next move, if this new comp. ever quits.

 

Since it's an OT system it should have an r4 original and rebuilds never were any good. If you want to use an r4, go new.
Never add all the oil to the compressor just a couple ounces and the rest in the pressure line so you don't "slugg" it. Always turn the shaft back and forth a dozen times just before starting for the first time.

 

You say the pressure is high, why would you change the compressor ? It may be making noise due to the hi pressure.

 

Buy new compressor IMHO

 

Thanks for your quick follow-up. My survivor is a 1980 with the typical (problematic) R4 compressor. Followed the installation instructions from my 1980 GM shop manual adding 2oz of oil to the new accumulator, then 4 oz into the compressor. We did not 'flush' the system with any cleaner. Just blew out the condenser and evaporator with compressed air. Everything seemed to flow well. Even the old orifice tube looked pretty clean after 30years without replacement. The car only has 42,000 original miles and the reason I decided to make the jump to a 134a conversion was I couldn't seem to keep the R12 in the system due to the poor R4 compressor seals. I always seemed to be replacing.

Seems that maybe where my mistake was seeing the R4 doesn't have a oil resovoir. Honestly, I didn't spin the compressor at all, simply took to the AC shop where they jumped the clutch sensor to engage the compressor, then began to charge the refrigerant.

I guess I'll take the compressor off and dump the oil and see if the compressor still makes a noise.

 

Before you remove anything, try just bleeding off some 134 until you get some decent pressures.
Don't know how experienced your shop is, but both sides with too high a pressure along with compressor noise etc usually just means an overcharge.
A bad compressor usually has a high low side and low high side with noise.
If you post readings @ 1500rpm it would help.

 

the system holds about 6 oz of oil,

If you didn't flush the oil from the other components and then added another 6 oz of oil for the conversion you may have a little to much oil. Although I have never seen this cause any serious issues with an AC system its possible I guess.

I have done a couple conversions were I didn't flush the system of the R12 oil and added the conversion oil to it, cooled fine for a while.

I agree with noonie, let a little out and see what happens. 2.75 lbs is allot for a vette. I just replaced the compressor, accumulator and orifice tube on my 99 Suburban and it holds 3 lbs 8 oz's of 134A with front and back AC.

When converting from R12 to 134A it takes about 65 to 75% of the indicated charge for R12.

Things to watch when the shop charges your system:

They should put a fan in front of the car blowing into the radiator with the AC selector on MAX, fan on high, engine RPM at 1500 and set the suction pressure at about 30 psi. The high side should be in the 225 to 275 psi area, as the cabin cools down the pressures both high and suction will drop a little with the temp.

If things are right the suction line between the compressor and the outlet of the evaporator should be cold and sweating.

Neal

 

Did you flush the system with a cleaning solvent before the conversion? I would make an uneducated guess that something is clogged in your condensor/evaporator lines and is causing high pressures and your compressor knocking. Compressor is most likely not bad though. Advance Auto has a can of flush (Citrus scent)that works great. You can use shop air to verify that it is clean and dry (Disconnect lines to compressor- Don't run flsuh thru the compressor!!!). You will need to re-add the oil you took out of the lines you flushed. Vacuum for a minimum of 30 minutes.

If you have not replaced the Low pressure switch, you should do so. Im told the old R12 switch cuts off at different pressure. They are pretty inexpensive and will save your new compressor from damage.

 

Please list the actual pressure(s) that you say are high.
If they are BOTH high, it is a symptom of an overcharge. An overcharged system will also make a compressor "rattle".
Also, air in the system will make both pressures high. Was it properly evacuated?
A bad compressor will also give you the same symptoms.
Confused ? Get both pressure readings at 1500 rpm's and post em here.
(a/c set on max cool)
Also take note if the low side hose from the accumulator to the compressor is cold and sweating, or not.

 

I used less than 2 lbs in mine. But I did go with a new crossflow condensor and the Sanden compressor. It will freeze you out now but until the new condensor was very ineffective.

 

Fellow vette owners, thanks again for all your feedback. It certainly helped! I worked with the vendor to return the defective remanufactured compressor. Ordered a new Delphi R4 from NAPA and it worked perfectly. Vacuumed the system, held a good vacuum and charged with just short of 3lbs 134a. About 80% of R12. Register temp is about 55 degrees. Pretty good for north central Texas heat.

Great advice from a great group of guys! Well Done