Stan944

I serviced my AC system, and have some questions to AC experts. I know there are a few guys here that have professional experience with AC.

Here is what I did:
remanufactured the compressor (shaft seal, large and small o-rings, internal gaskets), replaced most o-rings, added 4 oz of esther oil to the compressor, put r134a low and high fittings (after removing the shredder valves), and installed 1" shorter AC belt.

To check for leaks, I used a "vacuum pump" (essentailly an air compressor run backwards) that pumps down to 20 inch Hg. After ~24 hrs the pressure stabilized completely, making me believe I had no leaks.

Took the car to a shop for final (1 hrs) evacuation, and a few hours later added r134a from cans.

here is the problem:
I managed to add only about 1.5 cans of the refrigerant (12 oz of pure r134a and 1/2 can of r134a mixed with oil) , i.e ~20 oz, withing about an hour of running the engine. The low-side pressure was reaching 45 inchHg, and I didn't want to overcharge it.
The compressor was cycling on /off.
I know I should have added about 30 oz, so I didn't manage to put enough.

The system works (it chills), but it doesn't get very cold.

here is the question:
Because I didn't manage to put the recommended amount of gas, I think I had air in the system, not vacuum.
As I wrote earlier, I tested for leaks, and it's OK.
Now I'm questioning the evacuation procedure at the shop: I might be wrong, but I think they let air in while disconnecting the hoses.
At the end the guy did something to the machine, and I heard 'pssssss', i.e. the sound of venting the system. Then he disconnected the high side and low side hoses. I didn't hear any short 'pss' while he was disconnecting the hoses. I don't know how the hose couplings are constructed, so could he have let the air in when he had one of the hoses disconnected?

What do you think?
Thanks, Stan

AznDrgn

Was there a check valve in the line? was there a gauge manifold hooked up to the vacuum setup? if either one of those was present it is possible that they were just dumping the vacuum out of the pump and the lines but you should have still heard something when the connectors came off. Even if they let in a slight bit of air right when the pulled the connector the vacuum should be down so low that it is pretty much negligible. Just out of curiosity why did you remover the shredder valves? Out of all the AC conversions I've done the new fittings have just screwed on over the old ones and they would get depressed when the connector went on. When you took the cap off of the low side line to fill it did you hear a hiss? How often does the compressor cycle on and off? Take a thermometer and read the temperature coming out of the vents, it should be about 15 degrees below the ambient air temp.

83na944

Some R134a fittings have schraeder valves, and some don't. You can't have two inline, but you need one. With no schraeder valve, the refrigerant will leak out when you disconnect.

Sounds like you need to diagnose the system, or have someone do it for you. You'll need a gauge manifold for that. Could be that you expansion valve is stuck. And if you have air in the system, you could have too much moisture which would freeze in the evaporator or expansion valve, blocking flow.

I did this about a week ago. Had the R12 removed. Flushed the condensor. Replaced the drier. Replaced O rings. Pulled a 29.5 " Hg vacuum for an hour. Checked for leaks for a half an hour and then charged.

You should try for 930 g of refrigerant in the system. I never got all of the refrigerant out of can, so I used the better part of 3 cans to charge the system. IIRC, low side was about 45 psi. You also need too check the high side.

Peckster

It cost me $300 to have my system converted by a pro, it's worked great ever since.

944s2guy

it cost me 35 dollars and i did it a month and a holf ago.... so far it has worked amazingly..... we will see with time....

Stan944

Thanks for the replies:

FYI: I just did a temperature comparison between my 944 and Jeep YJ (2003): the "hand thermometer" feels almost identical in both cars! Maybe my expectation were too high?

I removed one shredder valve because the new angle fitting wasn't designed to push the old shredder valve during charging. The other? no real reason, simply why have two if you need one only?

I'm going to check for the temperature.
AznDrgn: did you mean 15 C or 15 F below ambient? This could be a good test. Anyway, ambient as measured INSIDE the car, not outside, because the air circulates within the car only (I think). Am I correct?

AznDrgn: yes, there was a vacuum gauge on his machine, and it red 30 "Hg even after he disconnected the hoses. Check valves? - I don't know. I'm still puzled whether there was good vacuum in my AC when I left the shop.

Thanks, Stan

Stan944

An additional question:
I remember that during charging, the low side pressure would rise if I reduced the cooling power on the **** at the console. I think it's normal, but could someone confirm?