A/C Compressor Question: Is my compressor bad?

[TIMSPEED]

So I went to repair my A/C in my newly acquired 97 SL2.
I went down and got new valve covers for the High/Low side ports, also got new O-Rings for the compressor fittings.
Replaced everything, then pulled vacuum (Have a nice RobinAir vacuum pump, with MasterCool manifold/guages). Done it correctly (vacuum for an hour; let it boil off moisture for 10 minutes; revacuumed for 30 minutes; made sure it didn't lose any vacuum.)
Went to fill it, and it took the specified amount (2½lbs) but the high side pressures never got above 80psi...
Now, I was reading through some posts, and read you have to charge it at 2000rpm...I didn't do 2000rpm, but I did ~1250rpm...
Now, is my compressor bad, or should I go back, revacuum and recharge at 2000rpm?
I always thought if the high side pressure never went up, the compressor is bad...no?
FDryer?

[scottyboost]

Basically speaking, a combination of 2 things makes pressure: The pump (compressor), and the oriface tube (or expansion valve). One of the 2 is faulty.

BTW, I wouldn't vacuum again just to check pressures at 2000rpm. Just hook the gauges back up.

What was the low side pressure when high was at 80?

[fdryer]

Here are some facts to deal with;

1-Verify that you have a variable displacement compressor (I cannot comment on information I don't have) as there is little information on how vdc's fail, if they fail at all. VDC's vary output displacement so even in winter time when the defroster turns on the a/c system, the compressor is outputting very little as it was designed to do to minimize engine load. The older R12 compressors are fixed displacement with full output that makes them less efficient than our vdc's being used now. If there's a problem with a vdc I don't know how to troubleshoot one. I will have to inquire around. A faulty compressor is one consideration.

2-The thermal expansion valve's purpose is to regulate the 'cool' in our a/c system and would have to be considered as another trouble spot. Its on the firewall where the two a/c hoses connect to the evaporator core.

What was the condition of the a/c system? What vacuum reading did you have after shutting off the pump? What was the reading after 30-minutes? 2 1/2 lbs. = 40ozs. Is this the correct amount needed for your system?

[TIMSPEED]

OK, I rechecked some things today...
After rapping on the compressor near the adjustment screw (below the LOW side port) I measured pressure, and the HIGH side was a little higher (110psi). However, vent temps were still warm.
It might be 2¼lbs...36oz's...I'd say I have right about 36oz in it.

[ssicarman]

The fill for the 97's should be 1.5 pounds if I recall correctly. Check the label to be sure.
The rpm's for filling don't necessarily matter a lot if you get the correct fill in.

What are your pressures at idle? High and Low side.

[TIMSPEED]

Originally Posted by ssicarman

The fill for the 97's should be 1.5 pounds if I recall correctly. Check the label to be sure.
The rpm's for filling don't necessarily matter a lot if you get the correct fill in.

What are your pressures at idle? High and Low side.

Whatever the correct fill is; is what I put in.
Idle pressures aren't MUCH different than 2000rpm..maybe 20psi?

[mg95SL2]

I'm going to defer to 'f' and 'ssicarman' on this, but I suspect you're now overfilled....
Are you talking two and a half pounds,(40 oz), or two and a half 12 oz cans (30 oz).
If I got my numbers correct, 24 oz (two 12 oz cans) and 6 1/2 oz of oil. Assuming you already have still some oil in the system... if you added two and a half 12 oz cans (30 oz) .... you've overcharged.
mike in fla

[fdryer]

What I'm about to suggest is for the professional using recovery equipment with weighing the amount of refrigerant used to ensure the correct amount is used. Its cannot be stressed enough that only the proper amount be used for a full system charge to utilize maximum airconditioning - any more than necessary only increases the high side pressures (dangerously) while increasing the load on the compressor, straining it and the engine with no more cooling effect than if the specified amount were used to begin with.

Someone on another site encountered this same condition of low pressures on both sides of the compressor when there should have been a large pressure differential - typical low side pressure would be 35-45psi while the high side would be 150-250psi@2k rpm, depending on outside temperatures. What was done; injecting more R134a than needed while running at 2,000rpm and closely monitoring both pressure gauges, especially the high pressure gauge. No excess amount was mentioned but continuously injecting R134a until the compressor 'kicked in' and displayed immediate rising of high pressure seemed to correct a problemmatic compressor that only displayed low pressure on the high side. This may pertain to vdc's. 'Kick starting' a compressor this way helped it to begin operating as designed but the excess refrigerant was released back into a recovery container and measured to ensure the remaining amount in the system was correct. The a/c system was successfully operating again.

When operating automotive airconditioning systems, high side pressures can easily exceed 250psi if not carefully monitoring the system and any mishandling of fittings can lead to catastrophic acidents. Be very aware of these high pressures. I can only speculate whether or not the compressor or expansion valve is stuck or needs some lubrication from within to get things going.

[TIMSPEED]

I vacuumed it all the way down and added 2½ 12oz cans (~30oz). If I overfilled, then it would have been perfectly filled after the second can...in which case, the HIGH side pressure was only like 50psi, and the vent temps were no cooler than ambient...
The only different tool a "professional" would have is a Scale...but I can get one of those also, since my entire family is/has been in Refridgeration all their lives...(just not Auto A/C...)
An interesting note, after I bought the car, I cleaned out the trunk, and I found a spare A/C Compressor. It was definately a PnP compressor, as it had the normal paint markings from PnP...so I'm wondering if they knew the compressor was bad. So, in any case, I know I'm going to have to revacuum and recharge, so I may try the other compressor, just to see if it makes any difference (only cost me my time and about $20 for more R134a...)