Is my A/C compressor dead?
10-01-11, 06:10 PM
#1
Full Member
Thread Starter
Is my A/C compressor dead?
I have been trying to track down the source of a problem I am having with my air conditioning on my 87 rx-7 gx. It has the sanden system with an sd-708 compressor, and at idle it blows approximately 2-5*C below ambient at the vents and the sight glass shows tons of bubbles. If I rev the engine to ~3000RPM the number of bubbles goes down and I can get 10-15*C below ambient, and if I get good airflow over the condensor at the same time (driving on the highway) I can get down to about 5-10*C at the vents (on a 30-32*C day).
I finally got the right fittings to measure the system pressures and here is what I have found:
The system has been charged (supposedly) with the correct amount of red tek, and was evacuated before filling, a new receiver/dryer has been fitted and the condenser was replaced with a used condensor due to a leak in the old one.
Outside temperature - 17*C
System off pressure 50psi both high/low
When I start the A/C the low pressure drops to 30-35psi and the high climbs to 70-75psi, with the high side needle jumping significantly (15-20psi variation)
If I rev the engine to 2500-3000RPM the pressures are as follows: 20-25psi low 100-120psi high and the variation on the high side goes down to 5-10psi
I now know the dangers of red tek so if I need to open the system I will be switching to r-152, but first I need to figure out if I need to replace the compressor or not. I checked the FSM and it says for R12 I should see 20-26psi low and 150-175psi high, but the red tek guys say I should see higher low side pressures and lower high side pressures, but cannot say by how much.
I vented a small amount of refrigerant and oil to check the condition of the oil and it is mostly yellow perhaps slightly light brown with no signs of black death or metal filings. 6oz of ester oil was added after replacing the receiver/dryer and condenser before charging the system.
So I am wondering, is my compressor shot or should I be looking elsewhere? My next thought was a bad expansion valve, perhaps it is stuck too far open? Or possibly something has jammed the reed valves in the compressor on one or more cylinders which may explain the large variation I am seeing on high side pressures?
What do you guys think?
Oh, one more thing that may be relevant. When I first kick the system on the return line from the evaporator gets nice and cold for about 15-30 seconds then warms up. This happens before the pressures stabilize.
I finally got the right fittings to measure the system pressures and here is what I have found:
The system has been charged (supposedly) with the correct amount of red tek, and was evacuated before filling, a new receiver/dryer has been fitted and the condenser was replaced with a used condensor due to a leak in the old one.
Outside temperature - 17*C
System off pressure 50psi both high/low
When I start the A/C the low pressure drops to 30-35psi and the high climbs to 70-75psi, with the high side needle jumping significantly (15-20psi variation)
If I rev the engine to 2500-3000RPM the pressures are as follows: 20-25psi low 100-120psi high and the variation on the high side goes down to 5-10psi
I now know the dangers of red tek so if I need to open the system I will be switching to r-152, but first I need to figure out if I need to replace the compressor or not. I checked the FSM and it says for R12 I should see 20-26psi low and 150-175psi high, but the red tek guys say I should see higher low side pressures and lower high side pressures, but cannot say by how much.
I vented a small amount of refrigerant and oil to check the condition of the oil and it is mostly yellow perhaps slightly light brown with no signs of black death or metal filings. 6oz of ester oil was added after replacing the receiver/dryer and condenser before charging the system.
So I am wondering, is my compressor shot or should I be looking elsewhere? My next thought was a bad expansion valve, perhaps it is stuck too far open? Or possibly something has jammed the reed valves in the compressor on one or more cylinders which may explain the large variation I am seeing on high side pressures?
What do you guys think?
Oh, one more thing that may be relevant. When I first kick the system on the return line from the evaporator gets nice and cold for about 15-30 seconds then warms up. This happens before the pressures stabilize.
10-01-11, 09:00 PM
#2
The high side needle fluctuations seem to me like a stuck TXV. It sounds like you know your stuff about AC systems, and it sounds like it's been evacuated and charged properly. One question, however. Did you (or whoever charged it) flush the lines, condenser, and evaporator out before charging it? It's very important that if there's anything in the lines either blocking flow, or could possibly get stuck in the little orifices or reed valves that it get out before charging. Luckily, you seem to have read jackhild's post on r-152, so a re-charge will be cheap. Just make sure that whatever you do, vacuum the sealed system off for a few hours at least to boil out any old red-tek.
10-02-11, 10:08 AM
#3
Full Member
Thread Starter
I think saying I know a lot about A/C systems would be a bit of an overstatement... I know enough to be dangerous which is probably the worst amount of knowledge to have when you combine it with me refusing to pay people to do something I can do myself 
I was thinking this over a bit last night and I should probably post a few more details here that may help:
The quest to fix my A/C started with replacing the receiver/dryer and evacuating the system, then having it charged with red tek, when this was done the system blew nice and cold for about 4-5 days then started to taper off. I pulled out my sniffer and found a tiny leak on the condenser (one of the fins was bent and put a tiny pin hole in a tube). This location was visibly leaking oil and I know I had run it for at least 4-5 hours as the system pressure dropped, so I suppose it may have been run low on oil for a bit there.
I located a used condenser and fitted it, it dribbled a tiny bit of oil once it arrived so I blew it out for about a minute with compressed air, only a small amount of clean oil spray came out, nothing else. I replaced the O-rings on both ends of the condenser and took it back to have the system re-charged. After this time the performance of the system was significantly worse, temps were only slightly lower than what I posted above. I took it back a few times and they fiddled with the charge levels (adding more or removing some refrigerant) however they were not able to get the temperatures to drop anywhere close to where they were the first time we charged it. I was usually close by as they were doing this work and at one point they were attempting to charge it until there were no more bubbles in the sight glass, and to do this it took system-off pressures of 110-130psi and low side pressures of 70-90psi when it was running. This sounded obscenely high to me and after that visit I refused to entertain this shop any more and started buying my own equipment to resolve this problem myself.
The A/C has been run for between 5 and 10 hours with varying levels of charge (but never low on oil) during the process of trying to figure out whether there was a problem, and trying to resolve that problem.
The compressor makes no abnormal noises, however when we first charged it and I turned on the A/C it would bog the engine down to the point that it would stall if I didn't keep my foot lightly on the accelerator and it made a noticeable difference in power, however at present it makes almost no difference in the idle, it will idle just fine on it's own with the A/C on.
I am really torn between the problem being a bad/stuck TXV or a bad compressor. Given the level of knowledge demonstrated by the people who have worked on this system I think it is possible that the compressor may have been liquid locked at some point and possibly the reed valves were damaged, or possibly a tiny bit of debris entered the system and jammed the TXV (although I thought usually this would cause massively high pressures on the high side), or maybe it is just a bad TXV that has failed in somehow and is wide open all the time.
What else can I do to further narrow this down? Am I at the point where I should start throwing parts at the system? Can the fluctuations be caused by one or more damaged reed valves or is that really plainly a TXV problem?
Since the TXV is ~$20 I am not terribly against replacing it to be certain that it is good, except that I can't tell from the FSM whether it can be changed with the A/C box in the car or whether I need to spend a couple hours yanking the entire assembly out. Also, I think I have factory installed air since it is the sanden system, is that correct? (Rock auto only distinguishes between the two as dealer or factory installed air when ordering a new TXV)
Thanks for the help so far, please keep it coming
I was thinking this over a bit last night and I should probably post a few more details here that may help:
The quest to fix my A/C started with replacing the receiver/dryer and evacuating the system, then having it charged with red tek, when this was done the system blew nice and cold for about 4-5 days then started to taper off. I pulled out my sniffer and found a tiny leak on the condenser (one of the fins was bent and put a tiny pin hole in a tube). This location was visibly leaking oil and I know I had run it for at least 4-5 hours as the system pressure dropped, so I suppose it may have been run low on oil for a bit there.
I located a used condenser and fitted it, it dribbled a tiny bit of oil once it arrived so I blew it out for about a minute with compressed air, only a small amount of clean oil spray came out, nothing else. I replaced the O-rings on both ends of the condenser and took it back to have the system re-charged. After this time the performance of the system was significantly worse, temps were only slightly lower than what I posted above. I took it back a few times and they fiddled with the charge levels (adding more or removing some refrigerant) however they were not able to get the temperatures to drop anywhere close to where they were the first time we charged it. I was usually close by as they were doing this work and at one point they were attempting to charge it until there were no more bubbles in the sight glass, and to do this it took system-off pressures of 110-130psi and low side pressures of 70-90psi when it was running. This sounded obscenely high to me and after that visit I refused to entertain this shop any more and started buying my own equipment to resolve this problem myself.
The A/C has been run for between 5 and 10 hours with varying levels of charge (but never low on oil) during the process of trying to figure out whether there was a problem, and trying to resolve that problem.
The compressor makes no abnormal noises, however when we first charged it and I turned on the A/C it would bog the engine down to the point that it would stall if I didn't keep my foot lightly on the accelerator and it made a noticeable difference in power, however at present it makes almost no difference in the idle, it will idle just fine on it's own with the A/C on.
I am really torn between the problem being a bad/stuck TXV or a bad compressor. Given the level of knowledge demonstrated by the people who have worked on this system I think it is possible that the compressor may have been liquid locked at some point and possibly the reed valves were damaged, or possibly a tiny bit of debris entered the system and jammed the TXV (although I thought usually this would cause massively high pressures on the high side), or maybe it is just a bad TXV that has failed in somehow and is wide open all the time.
What else can I do to further narrow this down? Am I at the point where I should start throwing parts at the system? Can the fluctuations be caused by one or more damaged reed valves or is that really plainly a TXV problem?
Since the TXV is ~$20 I am not terribly against replacing it to be certain that it is good, except that I can't tell from the FSM whether it can be changed with the A/C box in the car or whether I need to spend a couple hours yanking the entire assembly out. Also, I think I have factory installed air since it is the sanden system, is that correct? (Rock auto only distinguishes between the two as dealer or factory installed air when ordering a new TXV)
Thanks for the help so far, please keep it coming
10-02-11, 02:42 PM
#4
Were the condensers the same? I don't know Rx7 specifics, but if the condenser is a different type (maybe changed from s4-s5... idk) then the efficiency will be crap. Also, any time you chance using used parts for AC systems it's a crap shoot. I know a new condenser would run a great deal, but who's to say that the previous user of that condenser didn't shoot a can of AC stop leak through his system which coated the internal walls of the tubes?
10-02-11, 11:11 PM
#5
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Thread Starter
The condensers were identical, both were from the same year sanden systems and matched as far as I could tell. I called every shop in the yellow pages and my only option was to buy a universal condenser or to buy one from the dealership for $450. Neither was a good option.... I don't think there was any stop leak in the condenser I bought, though I guess it would be hard to tell once it has dried. I will remove and inspect the txv before I declare the compressor dead. Do you know if I can remove it with the a/c box in the car?
05-17-12, 10:16 AM
#7
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Thread Starter
So I finally got around to looking into this. According to what I was seeing either the compressor was NFG or the expansion valve is stuck wide open. Being that the expansion valve is much cheaper to replace I removed the evaporator box and opened it up and removed the expansion valve but it looks like I have bought the wrong one to replace it. I have one for factory air and it would appear I actually have dealer installed air on my car... The expansion valve I have physically fits and the flow direction is correct however it sits a little bit close to one of the lines.... Can I use it? It would install rotated 90* to the original valve but the flow direction would be correct from what I can tell.
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05-17-12, 02:53 PM
#9
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Thread Starter
If I replace the compressor I will need a Sanden SD708 with the single bolt rear connector. This seems to be a bit of a rare one, but if yours fits what would you want for it? Keep in mind I am up in the far north (Calgary, AB, Canada) so shipping might cost a few bucks, and I can only accept things shipped via US Post as UPS/FedEx charge excessive brokerage fees. If yours has the double connectors I would need both of the lines that bolt on to the compressor as well.
I am going to try to verify whether the compressor is bad in the next couple days I hope.
I am going to try to verify whether the compressor is bad in the next couple days I hope.
05-17-12, 09:55 PM
#10
The whole f-n problem is the REdtek crap
And there is no telling what was in that used condenser. In it's previous life it could have been clogged, it could have PAG/R12 residue in it. Additionally, you have don't know what the petroleum solvent in the redtek dissolved and caused to move around in the system. 
The drier should have caught any thing that came out of the compressor or the condenser.
Flush the condense or better yet get a replacement, replace the TXV. Replace the drier.
I know you can have bent valves in a compressor, but I have never seen it in a Sanden on an FC.
The single bolt sanden is pretty common around here, you won't have trouble finding one used on the board.
Try JustJeff. I think he is working on a project that may leave him with a spare Sanden.
The drier should have caught any thing that came out of the compressor or the condenser.
Flush the condense or better yet get a replacement, replace the TXV. Replace the drier.
I know you can have bent valves in a compressor, but I have never seen it in a Sanden on an FC.
The single bolt sanden is pretty common around here, you won't have trouble finding one used on the board.
Try JustJeff. I think he is working on a project that may leave him with a spare Sanden.
05-18-12, 09:39 AM
#11
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Thread Starter
Jack, thanks for chiming in
The condenser was allegedly removed from an untouched working R12 system when the car was parted out and as far as I could tell it was clean, compressed air yielded just a tiny bit of clean oil and the ends showed no sign of stop leak.
I could change the drier again just to be safe.
As for the TXV: I appear to have bought the TXV for factory installed air while I actually have dealer installed air. The difference is that the bulb is a coil of wire instead of an actual bulb, and the TXV mounts backwards to how the original one did. Does this actually make any difference?
I removed the old TXV and stuck the bulb in a freezer to get it down to about -20*C and then warmed the bulb with my hand until it felt completely warm, I was unable to see the valve inside move when it changed temperature so I tried a few times. Also blowing air through it feels no different with the bulb warm or cold. Does this mean my old TXV was dead? I didn't think to try this with the new one before fitting it to the car so I have nothing to compare to.
The condenser was allegedly removed from an untouched working R12 system when the car was parted out and as far as I could tell it was clean, compressed air yielded just a tiny bit of clean oil and the ends showed no sign of stop leak.
I could change the drier again just to be safe.
As for the TXV: I appear to have bought the TXV for factory installed air while I actually have dealer installed air. The difference is that the bulb is a coil of wire instead of an actual bulb, and the TXV mounts backwards to how the original one did. Does this actually make any difference?
I removed the old TXV and stuck the bulb in a freezer to get it down to about -20*C and then warmed the bulb with my hand until it felt completely warm, I was unable to see the valve inside move when it changed temperature so I tried a few times. Also blowing air through it feels no different with the bulb warm or cold. Does this mean my old TXV was dead? I didn't think to try this with the new one before fitting it to the car so I have nothing to compare to.
06-05-12, 12:53 PM
#12
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Thread Starter
A quick update to this - I finally got around to doing some further testing and my compressor is toast.
I had 2 other R12 compressors sitting on a shelf in my garage from past project cars (unfortunately incompatible ones, but that part doesn't matter here) so I spun them by hand and found that they both had no problem generating 10-30psi on the outlet port with just a couple slow turns by hand (after which I had trouble keeping a good seal with my pressure tester on the outlet port), so I removed the compressor from my rx-7 and I couldn't get it to produce any pressure when turned by hand, and it made pretty much no noise instead of the rhythmic POP-POP-POP that the other ones made. I tried spinning it with an impact gun and managed to get it to produce about 2psi, but if I took the pressure gauge off it still barely moved any air at all. I drained the compressor to check the oil level and found it was lower than I would have expected so I topped it up with oil and tested again, still no pressure.
I had 2 other R12 compressors sitting on a shelf in my garage from past project cars (unfortunately incompatible ones, but that part doesn't matter here) so I spun them by hand and found that they both had no problem generating 10-30psi on the outlet port with just a couple slow turns by hand (after which I had trouble keeping a good seal with my pressure tester on the outlet port), so I removed the compressor from my rx-7 and I couldn't get it to produce any pressure when turned by hand, and it made pretty much no noise instead of the rhythmic POP-POP-POP that the other ones made. I tried spinning it with an impact gun and managed to get it to produce about 2psi, but if I took the pressure gauge off it still barely moved any air at all. I drained the compressor to check the oil level and found it was lower than I would have expected so I topped it up with oil and tested again, still no pressure.
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