dirkdaddy

I am working a buddy's 78 Rolls Royce for a side job. It has a GM A6 compressor and GM AC components. It is a R12 unit. It was cooling some but then barely is cooling after just a few minutes.

I have tested the system and the pressure on the high and low sides is the same. The compressor engages, the condenser input gets hot, the output stays pretty cool, but I"m not getting much draw from the low side as the pressure is too high to put any in it.

The system is in pretty good shape with some new hoses, I have used a sniffer for leaks found none except the valve cores which I replaced with one of those tools.

I am thinking I need an expansion valve. And while at it, maybe put in a POA valve.

Any advice?

ps. Yes I have access to friend's recovery system and a small supply of R12 for this one job. The C2 is converted to 134a VA system.

DD

Mike Geary

I think the expansion valve being stuck open is the most likely cause.
It's not closing down the orifice to drop the pressure and is overfeeding the evaporator.

Are you seeing 200+psi on the suction side?

dirkdaddy

I could not get much into the system it was about 100 lbs on both sides.
So the expansion valve can open that much, its not just an orifice?

dirkdaddy

I am going to replace both the expansion valve and poa if I can find them.

Mike Geary

I agree, and while the system is open I'd do a gross test of the compressor: engage the clutch, spin it by hand with your thumb over the discharge port and see if you're getting output pressure. I assume the compressor is not making bad sounds?

dirkdaddy

Ok my normally go-to parts store, the Ac Delco place with guys who have worked there over 30 years and are ASE trained, they raised eyebrows at my AC parts. They have not seen POA valves in years, and they can get expansion valves but mentioned there is a way to convert it they thought to an orifice type system. I have looked online and see some expansion valves and rebuilt POA, so I may be able to get it setup. The parts guys said that even back in the day of these parts they remembered them being troublesome. Great. I could convert the whole thing to R134a I guess if I found a compatible condenser and got the appropriate hoses and fittings, flushed the whole deal out. I'm still looking. The messed up part is that Rolls used GM parts, so its probably available but what vehicle they are off of is anyone's guess so it makes it double hard. The expansion valve from a '75 suburban looks like the one. Now on to the POA valve. I am not sure if its defective or not, the only control is the tubing fitting from the expansion valve, not sure how all that works I was reading something about how it senses if the evaporator is getting below like 29 degrees it shuts down until it warms up a bit. Guys at the parts desk were fogged in memory banks from training and experience on those many many moons ago.

DD

Powershift

I think you got yourself a tough project.

From what I saw in earlier posts, it looks more like the compressor is not pumping than anything else.

I would remove the expansion valve and do two things:

1. Check to make sure the inlet screen is clean. They can be cleaned and new ones are available. I can provide part numbers if needed.

2. Put the expansion valve bulb in ice water and then warm it with a hair dryer. See if this makes any difference in your ability to blow through the valve. It should be open when warm and should (almost) close when temp bulb subjected to ice water bath

For the POA. Not certain you need a new or rebuilt one. Classic Auto Air in Florida can test yours and also provide a rebuilt unit. Pacecar Jeff on Ebay also sells used and tested POA. There are three (3) different POA that I know of. The only difference is the location of the various side fittings. They all have the same fittings, but the location/orientation is different.

You can test the POA yourself, but it requires a small test setup. In your case, it may be better to send to Classic Auto Air for evaluation and rebuilding if needed.

If you do go to 134a, clean and flush out the system of the R-12 oil, and then use ESTER oil for the 134a. Replace the drier, and have the POA recalibrated for 134a.

A lot of the info you seek is in the archives. Check Jim Geary's name or my name or 62Jeff or Mechron. That should provide you plenty of reference information.

Larry

Mike Geary

DD:

If your TXV fails the testing Larry outlined, check out expansion valve 25-0057 offered by Old Air Products.

Mike

dirkdaddy

Thanks guys am looking at this now will update. I think the compressor was working as the condenser input pipe would get hot, but there was no high/low side it was all about 90psi so wondering if the valves were opened up too much if that is possible. The AC was also working some before teardown, it just wasn't getting really cold.

dirkdaddy

Update:

I found a local vendor for OldAir products and purchased a new POV valve eliminator, new expansion valve, dryer and a few other small goodies, I drew system down 28 inches vac for over an hour and then charged. It works ok at first, but then gets really warm. The dual fans I installed are working fine.

I have figured out the condenser does not seem to be cooling very much despite two fans. The fins are very close together, and I think with all the years on this car they are clogged or something. I am getting abotu 150+ degrees going into it, and only about 145 coming out.

So looks like I will need a new condenser. Its a top-connected unit and only 10x20 so its going to be a challenge to find one fitting inside the grill shell of the Rolls. I have found a 12x20 going remove the grill and measure again. Most replacements are side connected which is going to require more fittings...

dirkdaddy

I installed all the new parts, exp. valve, POA eliminator, 13x20 condenser, drier, dual 9" fans, custom hoses. I vacuumed the system and got it to hold steady just about 30 inches for over an hour. I put in 134a and 4 oz of PAG oil. I did not flush the system the guys at the Old Air dealer sold me oil that was compatible. I was also told that roughly 2oz for a drier and same for condenser = 4 oz. This was a rough guide for how much oil to use told to me by some crusty old ASE counterman at a trusted parts shop. I charged and am getting about 200 on high side and 35 on low side at about 80 degrees. This came out to only about 1.75 cans of 134a.

The AC cools some, starts out in 40's but then as car warms up it goes to about 50 degrees and struggles to really keep up. I realize the condenser is small, but the grill area I have to work with is also small and that was the biggest I could fit. The car is pretty big. I am seeing high temps coming out of the condenser which I think is the problem. 155 going into it, and about 135-140 coming out. I have new dual pusher fans mounted flush to the front of the condenser.

* Idea one - I have been told conflicting information on the placement of condenser and each has merit. One that the condenser needs to be about .75 to 1.25" from the radiator to keep the heat from the car from passing through to the condenser. The other advice was opposite, put the condenser right up against the radiator so that the flow of air has to go through it at highway speeds, not around it.

Also, I have clamped shut the heater hose this Am to see if that does anything. Perhaps the car is reheating the aircon.

On the auto a/c forums a guy suggested a flush and get all oil out, then refill it. I may try that if I can get a local shop to do that today.

THoughts anyone? Most likely issue?