r134 A/C Diagnosis, High Low-Side Pressure, Opinions?
04-30-2009, 11:11 PM
#61
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R12 or 134?
And this depends on ambient temp.
Here is the R12 chart for low and high side followed by the high side R134 chart. With the engine off they should equalize pretty quickly.
05-01-2009, 04:05 AM
#63
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05-05-2009, 12:26 PM
#64
BTW, I sympathize with your issue and frustrations, but this has been the BEST 928 A/C thread EVER!
-Ken
05-05-2009, 09:19 PM
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05-06-2009, 12:12 AM
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What follows is a description of how I forced out excess oil from the A/C system (along with some opinions and guesses...) It is from memory so I may have missed something. If something doesn't make sense then post it; it may help me remember.
Caveat One: you should only do this if you have collected data that rules out other causes of poor A/C system performance. Why? Because once you do this, you will not have a good idea of how much oil is left in the system. The A/C system can run well with less than the spec amount. But, it does need some oil to keep the compressor lubed. You will have to guess. I was able to make a slightly-educated guess (details below.) So, caveat emptor, and if your compressor shreds itself don't come back cryin'.
Caveat Two: This procedure seems to have worked for me. For now. It doesn't seem to have broken anything. But, I won't be surprised if someone points out something that isn't so good. (And if something about this strikes you as not good, then post it and let's discuss.)
You will need:
- Regulated compressed air.
- A method of introducing the compressed air to the low-side of the A/C system.
- (optional) An air wand attachment for the air hose with one of the rubber tips.
For the first item, as far as I can tell, most compressors these days come with an integral pressure regulator. You don't need biomedical precision, you just need to be able to control the pressure to the 5 to 15 PSI range (maybe a bit higher.)
For the second item, what I did was to use an adapter (available at any good suburban hardware store) to fit a standard air-hose coupling to one of the little hoses with the r-134 fitting you can get along with a bottle of r-134. (As no ozone was harmed during this procedure I opine that this bit of hackery is within the spirit of the 609 regs.) (If you've got r-12 fittings you'd gobble together something with a low-side r-12 coupling.)
The third item is usually part of the accessory kit shipped with compressors.
What I did:
Remove the receiver/dryer. You'll have to replace it anyway. Results may vary if you leave it in during the procedure and you'll have less idea of how much oil you get out of the system. And yes, you'll need to replace it when you're done.
Uncouple the high-side A/C hard-line from the under-passenger-seat coupling that's under the car. Place a clean catch pan under it. (If you don't have rear A/C then, I guess, you'd need to disconnect the high-side hose from the compressor and place the pan under it.)
Use a rubber plug (or your thumb later) to plug the high-side hard-line that was coupled to the output of the receiver/dryer.
Zero-out the pressure regulator on the compressor.
Attach the air hose to the adapter hose and then connect the r-134 fitting to the r-134 low-side port.
Adjust your regulator to ~10 PSI.
At this point you're forcing air through the low-side, back through the front expansion valve, front evaporator, into the high-side and then (with rear A/C) to the low point in the system where you've disconnected the hard-line. (There is some leakage through the compressor, but not a lot.)
I ran the compressed air for 20 minutes or so and got a bunch of oil out.
Next, turn on the ignition (just to 'running' not to 'start') and turn on the rear A/C. This opens up the valve to the rear evaporator and thus you're forcing air through the rear expansion valve and evaporator and down to that de-coupled low point again.
I let that run for another 20 minutes or so, then did a lather rinse and repeat of both front and rear one more time.
I then disconnected the input line to the condenser and used the air wand to blow it out. I didn't get more than a few drops out though.
Replace the o-rings on the high-side hard-line under the car, condenser, and reconnect them.
Next, remove the compressor and drain the oil.
Dump all your drained oil into a graduated cup and see how much you get out. (Mostly for curiosity sake.)
Take your best guess at how much oil is left in the system. Subtract that amount from the spec amount of oil and add the resultant amount of new oil back into the compressor. Re-install the compressor. Install your new receiver/dryer and then proceed to vacuum, fill, test.
What *I* did for my best guess was to assume that I removed only _excess_ oil from the system and that both evaporators and the condenser still had a spec amount of oil coating their insides. I then added the spec amount of oil for a new compressor and a new receiver/dryer.
However, I also have A/C oil phase testers:
http://autorefrigerants.com/oilphasetester.htm
(Credit goes to Earl Gillstrom for showing me these along with appreciation for lots of listening to me gripe about this car's A/C system.)
The testers will give you some indication of oil level and condition. I've tested the system three times (and about 300 miles) and the testers tell me that my oil level isn't too low and is in good shape. (And the A/C is still freeze-your-*****-off cold.)
Caveat One: you should only do this if you have collected data that rules out other causes of poor A/C system performance. Why? Because once you do this, you will not have a good idea of how much oil is left in the system. The A/C system can run well with less than the spec amount. But, it does need some oil to keep the compressor lubed. You will have to guess. I was able to make a slightly-educated guess (details below.) So, caveat emptor, and if your compressor shreds itself don't come back cryin'.
Caveat Two: This procedure seems to have worked for me. For now. It doesn't seem to have broken anything. But, I won't be surprised if someone points out something that isn't so good. (And if something about this strikes you as not good, then post it and let's discuss.)
You will need:
- Regulated compressed air.
- A method of introducing the compressed air to the low-side of the A/C system.
- (optional) An air wand attachment for the air hose with one of the rubber tips.
For the first item, as far as I can tell, most compressors these days come with an integral pressure regulator. You don't need biomedical precision, you just need to be able to control the pressure to the 5 to 15 PSI range (maybe a bit higher.)
For the second item, what I did was to use an adapter (available at any good suburban hardware store) to fit a standard air-hose coupling to one of the little hoses with the r-134 fitting you can get along with a bottle of r-134. (As no ozone was harmed during this procedure I opine that this bit of hackery is within the spirit of the 609 regs.) (If you've got r-12 fittings you'd gobble together something with a low-side r-12 coupling.)
The third item is usually part of the accessory kit shipped with compressors.
What I did:
Remove the receiver/dryer. You'll have to replace it anyway. Results may vary if you leave it in during the procedure and you'll have less idea of how much oil you get out of the system. And yes, you'll need to replace it when you're done.
Uncouple the high-side A/C hard-line from the under-passenger-seat coupling that's under the car. Place a clean catch pan under it. (If you don't have rear A/C then, I guess, you'd need to disconnect the high-side hose from the compressor and place the pan under it.)
Use a rubber plug (or your thumb later) to plug the high-side hard-line that was coupled to the output of the receiver/dryer.
Zero-out the pressure regulator on the compressor.
Attach the air hose to the adapter hose and then connect the r-134 fitting to the r-134 low-side port.
Adjust your regulator to ~10 PSI.
At this point you're forcing air through the low-side, back through the front expansion valve, front evaporator, into the high-side and then (with rear A/C) to the low point in the system where you've disconnected the hard-line. (There is some leakage through the compressor, but not a lot.)
I ran the compressed air for 20 minutes or so and got a bunch of oil out.
Next, turn on the ignition (just to 'running' not to 'start') and turn on the rear A/C. This opens up the valve to the rear evaporator and thus you're forcing air through the rear expansion valve and evaporator and down to that de-coupled low point again.
I let that run for another 20 minutes or so, then did a lather rinse and repeat of both front and rear one more time.
I then disconnected the input line to the condenser and used the air wand to blow it out. I didn't get more than a few drops out though.
Replace the o-rings on the high-side hard-line under the car, condenser, and reconnect them.
Next, remove the compressor and drain the oil.
Dump all your drained oil into a graduated cup and see how much you get out. (Mostly for curiosity sake.)
Take your best guess at how much oil is left in the system. Subtract that amount from the spec amount of oil and add the resultant amount of new oil back into the compressor. Re-install the compressor. Install your new receiver/dryer and then proceed to vacuum, fill, test.
What *I* did for my best guess was to assume that I removed only _excess_ oil from the system and that both evaporators and the condenser still had a spec amount of oil coating their insides. I then added the spec amount of oil for a new compressor and a new receiver/dryer.
However, I also have A/C oil phase testers:
http://autorefrigerants.com/oilphasetester.htm
(Credit goes to Earl Gillstrom for showing me these along with appreciation for lots of listening to me gripe about this car's A/C system.)
The testers will give you some indication of oil level and condition. I've tested the system three times (and about 300 miles) and the testers tell me that my oil level isn't too low and is in good shape. (And the A/C is still freeze-your-*****-off cold.)
05-06-2009, 12:34 AM
#67
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By the way, this may or may not be the best A/C thread. But, if it is, the thread - and my eventual success - is due to the folks that stuck with this thread and provided "brain time." In particular Dan and Zeus.
Thanks! And beer (or beverage of choice) at SITM.
(Crap, I need to start a thread on how to hook up a keg 'fridge to the 928's A/C system: I owe beer to a lot of folks
)
Thanks! And beer (or beverage of choice) at SITM.
(Crap, I need to start a thread on how to hook up a keg 'fridge to the 928's A/C system: I owe beer to a lot of folks
)
05-10-2009, 07:45 PM
#69
I'm thinking through the excess oil removal procedure, and I'm looking at the refrigerent flow ( Page 87-1 of the WSM). I have a front only system, and a Kuehl compressor. Could I not just open the drain valve at the bottom/rear of the compressor and apply the air pressure as you described, instead of removing the high side hose from the compressor? With my car up on ramps, this is the lowest point in the system.
-Ken
-Ken
Last edited by KenRudd; 05-10-2009 at 08:24 PM.
05-10-2009, 09:27 PM
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Hmmm... I don't know. I don't know how much air flow you will get through the compressor. In any case, at the end of my procedure I dropped, drained, and re-filled the compressor. So, I'd probably start there, and plug the low side compressor hose - or use that rather than the port to introduce the air.
05-11-2009, 12:28 PM
#71
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I'm thinking through the excess oil removal procedure, and I'm looking at the refrigerent flow ( Page 87-1 of the WSM). I have a front only system, and a Kuehl compressor. Could I not just open the drain valve at the bottom/rear of the compressor and apply the air pressure as you described, instead of removing the high side hose from the compressor? With my car up on ramps, this is the lowest point in the system.
-Ken
-Ken
Personally though, I think it would be safer to flush each component separately. The receiver/drier may also cause problems with the above approach. I've also seen some expansion valves that are not easily flushable. If you flush separately and just replace the expansion valve(s) and drier with new ones, you can't go wrong.
Dan
'91 928GT S/C
475hp/460lb.ft
05-11-2009, 12:52 PM
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Ken, Dan,
let's distinguish between a "flush" and "removing excess oil with air". The former is the procedure in which you use a chemical agent to remove the oil. The latter should only be necessary if you do a ****-poor job of "flushing" (like I did, apparently.)
In the former case, you definitely cannot have the compressor, expansion valves and r/d in the flushing loop as the chemical agent can (or will) damage them. In the latter case you can since air isn't going to cause damage. In either case, the compressor is going to block flow if it is in the loop.
let's distinguish between a "flush" and "removing excess oil with air". The former is the procedure in which you use a chemical agent to remove the oil. The latter should only be necessary if you do a ****-poor job of "flushing" (like I did, apparently.)
In the former case, you definitely cannot have the compressor, expansion valves and r/d in the flushing loop as the chemical agent can (or will) damage them. In the latter case you can since air isn't going to cause damage. In either case, the compressor is going to block flow if it is in the loop.
