Compressor or Clutch

[ant-live]

I'm having compressor issues and my mechanic says i need a new one. How do you determine if it's the compressor or the clutch that going bad?

 

[fricker66]

When my clutch went, it went out with a bunch of noise and smoke. As far as figuring out what happened, I noticed the a/c wasn't being engaged. (No lug on the engine when trying to cycle the a/c) When my parents lost their compressor, the clutch was still cycling on for a split second until the compressor refused to move. If you've taken it to a reputable mechanic, he should be able to diagnose this for you without any problems. Best of luck.

 

[rangerj]

A good A/C compressor should ratate freely at 7 foot pounds (84 inch pounds) of torque. This test should be done with the compressor off of the vehicle, but you can do this test with the belt loosened or removed and the system still under pressure. If it takes 7 pounds of torque, or less, to ROTATE (not starting torque) the compressor, then it is most likely OK. If the compressor is hard to rotate, or is siezed, then it is in need of replacement. If you replace the compressor, you will also need to replace the filter/dryer, and will need to flush out the rest of the system. It would be a good idea to replace all "O" rings and springs, when the connections are put back together after the flushing. Also consider converting to R-134a, if you have an R-12 system. Hope this helps, rangerj

 

[NiNeTy Fo SHO]

What all do you really have to do to convert from a R12 to a R134A? I really have no clue...do you just buy a conversion kit?

 

[rangerj]

Part 2 the clutch question.
Does the clutch engage? If not, is the clutch coil getting 12 volts? Is there suficient pressure in the system to activate the low pressure switch? This switch can be "jumped" if the system pressure is to low to activate the switch. Is the clutch pulley bearing siezed, or does it rotate freely. If the pully will spin freely, but will not turn when the clutch is engaged, it is the compressor. You can activate the clutch coil, with the car off, by connecting 12 volts to the coil directly. This will tell you if the coil is working, and if the clutch will engage and disengage also. rangerj

 

[rangerj]

R-134a conversion from R-12?
If your R-12 system has leaked down, or a component of the system needs to be replaced and the system has to be opened up, then it is a good time to consider converting to R-134a.
If the system failure is due to a simple leak, the rest of the system componants are in good shape you can simply fix the leak, drain the R-12 oil out of the compressor, put R-134a oil (7 to 8 ounces) in the compressor, vacuum the system at 30 inches of vacuum for 30 to 45 minutes (I like to do 30 and let the system set for 30 minutes to check for leak down, then vacuum for another 30 minutes), then recharge the system with about 85% of the amount of R-12. I like sdpatt's approach, that is to charge the system with R-134a until you get a low preasure reading of 50 PSI, and a high pressure reading of 240 PSI, and the temperature coming out of the dash of about 37 degrees. The better way to do the conversion would be to replace the filter/dryer, and to flush the entire system, with the exception of the compressor. DO NOT CLEAN the Compressor, just empty it by letting it drain overnight. Replace all "O" rings and springs at the connections. Did I remember the pressures right Scott? rangerj

 

[Cobria]

What's the proper way to measure pressure on an ac system? What tools does it take?

 

[rangerj]

Measuring A/C pressure.
A/C pressures are measured with a set of guages attached to a manifold. The low pressure guage includes a negative pressure reading (vacuum). The hoses are color coded, that is red for high pressure, blue for low pressure, and yellow for vacuum or adding gas. The sets are made for R-12 or R-134a. The high side coupler and the low side coupler are different sizes. The couplers for R-12 and for R-134a are different sizes also. The R-134a connector is actually a quick connect type of connector. You cannot mix up the two. If you want to work on both systems you will need two sets of A/C guages/manifolds. J. C. Whitney sells the R-134a set for about $100 (Maybe a little more or less as I remember. I've had my R-134a set for about ten years). As R-12 is becoming outdated, the cost of R-12 manifold/guages has dropped. You can stick your finger in a light socket and tell if the electricity is on. Or you can use a volt meter and get a lot more useful information about the system! rangerj

 

[naval-avi8or]

rangerj:
Part 2 the clutch question.
Does the clutch engage? If not, is the clutch coil getting 12 volts? Is there suficient pressure in the system to activate the low pressure switch? This switch can be "jumped" if the system pressure is to low to activate the switch. Is the clutch pulley bearing siezed, or does it rotate freely. If the pully will spin freely, but will not turn when the clutch is engaged, it is the compressor. You can activate the clutch coil, with the car off, by connecting 12 volts to the coil directly. This will tell you if the coil is working, and if the clutch will engage and disengage also. rangerj

There is one exception. If the the clutch is worn out causing the air gap to be out of spec then the coil can not creat a strong enough magnetic feild to engage the clutch.

 

[95SHOdude]

ant-live:
I'm having compressor issues and my mechanic says i need a new one. How do you determine if it's the compressor or the clutch that going bad?

HI, I've changed out two SHO compressors since I've owned my car (it's hot here). Once the clutch was bad the other time the compressor. What year is your car? If it's a gen II or III it's probably R-134A. Just open your hood and there should be a sticker that tells you what you have, should be on top of the radiator cover just right of the latch. For a gen II (mine) the low pressure connector is under a cover on the firewall (three screws and it's off). The high pressure fitting is just in front of the battery. The entire system shouldn't take more than 2 lbs if empty (2 cans). I wouldn't fill the system till the low side reads 30-35 psi (I think 50psi is a little high). All the trouble shooting I've heard so far is good advice. As long as the compressor isn't locked up you should be able to engage the clutch (broom handle trick works good for testing the gap). If it's the gap, just pull off the clutch (can give details or check SHOTimes) and remove a spacer, that solved my problem last time. If it is your compressor you'll probably only be able to get a rebuilt one for $250 -$300 (normally come with a new clutch). To replace the o-rings you will need a special tool (at least it makes it easier). It's about a day job to do everything from replacing the compressor to filling up the system. If you've never done an A/C I'd have someone who has help or take it in. But on a SHO be ready for a big price tag. I paid to have my first compressor replaced, had the A/C on during a hard run and it blew up... . That cost me over a grand. When I did the work myself I spent less than $300. In any case let us know if any of the trouble shooting gives more insight. Sorry for the long post. I've just been through a lot with my A/C so I'm familar with about every part of it.

 

[rangerj]

Naval-avi8or,
You are right, I missed the #3 wire on this one. The gap between the clutch faces gets wider with wear. If it gets too wide, then the coil will not pull in the clutch face. This is a good reminder as to why setting the gap is important, and why checking the gap when you have a clutch that will not engage. A salute and thumbs up to you. rangerj