I converted my A/C to R134 last year and everything was working fine until winter came. This summer it stopped working. I figured the R134 leaked out but after some checking I see that the pressure switches are closed and there is power to the coil. The ground to the coil is ok too.

The service manual says that the resistance of the coil should be 3.6ohms at 70* - mine is 4.6ohms at 85*ish.

Any ideas? Sounds to me like the clutch or coil is dead. Does this make sense?

Thanks!

 

Did you put a set of gauges on the the system?
See what your pressure is before you go for a compressor.

 

Providing there is R134a in the system, there is a sensor that malfunctioned on my 90 that is supposed to sense the amount of freon that's in the system. If it quits, the compressor won't engage. I replaced mine for $12 and the air conditioner works fine now.

 

Thanks for the input, all!

There is a Low Pressure Cut-out switch on the low side but it is closed (system charged). The High Pressure Cutout is also closed (normal when compressor not running). There is power and ground to the compressor coil connector when the AC is requested but the compressor never engages.

The compressor turns by hand just fine and I can hear it "working".

I don't have a set of gauges handy - I rented a set form AutoZone when I converted to 134 last summer. I would guess that the system is charged because the Low Side switch is closed. I bought the switch calibrated for 134 so it should be OK.

 

Ttt

 

could the "freon detector switch" cause the same problem in a 91 ? i bought mine a year ago, it had no a/c, mechanic said he reset the computer, and lo and behold, i had a/c, but tried to use it for first time this year, on sunday, nothing but hot air.

 

'90 and up rely on a pressure switch to monitor charge level and several other functions. It gets a 5 volt reference from the ECM and normal operating range is about .8 to 4 volts. Each volt is about 100 psi and if the system goes below or above the operating range, the ECM won't engage the clutch relay and a trouble code will usually set. System also monitors the low pressure switch for rapid cycling and the ECM will shut it down if the frequency of the on/off time indicates a low charge. First thing to do is to disconnect and reconnect the battery and then see if it engages. If so, one of the a/c codes has set turning the system off (most likely low charge). If not, momentarily depress the schrader on the low pressure switch to make sure there is something in it. If so, ECM grounds the relay that engages the compressor and monitors clutch engagement to make sure that it happens. Check for Code 68 - 69 which the ECM can set for a faulty relay or if there is a problem in the relay circuit.

 

I don't think that the 90 is quite that advanced. I did check the codes and there was no code 09 for low freon or any other thank heavens. The shop manual says it gets this from the cycling frequency of the AC On parameter in the ECM datastream which it gets from monitoring the voltage to the compressor coil.

In my case the voltage to the compressor connector is fine as is the ground but the compressor never turns on. Everything electrical is working but the compressor never cycles.

 

You did look for the 09 code on the C68 controller and not the ECM (SES light), right?

 

Yes.

I held the fan up and down buttons for 5 sec - display showed -00 then I hit the auto fan button and it went to 00 or no codes to display

No SES codes either - the engine is one of the few things working on this car.

 

If you measure 12 volts at the Compressor Clutch connector and the Clutch doesn't engage, the only thing it could be is

1)The diode across the Clutch coil could be bad. To test, cut one lead of the diode.

2)The air gap of the Clutch plate and the Clutch coil is to big. Measure with a feeler gage, should be .02 inches +- .006

3)Clutch coil is bad. Usually you can smell it if it's burnt.

4)The ground for the Clutch coil is bad.

 

Hello ! Unplug the connector on the compressor , using a VOM , connect the leads to the clutch coil terminals , and see if it "zero's " out , if it doesn't , time for a coil ! You can replace it in about an hour without taking the compressor out !

 

1) Didn't think about the diode - I'll give that a try tomorrow. That would be a nice easy fix.

2) Not sure how to check this. I assume I have to pull the pressure plate and coil apart. Might try that tomorrow too.

3) No strange odors or noises nearby.

4) I checked the connector and got continuity to ground.

Looks like I will probably need to start pulling stuff apart tomorrow. High tomorrow is 99* - this should be fun.

 

Not sure what you mean by "zero out".

If you mean checking the resistance - I mentioned in the first post that I got 4.6 Ohms at 85-90* and the GM spec is 3.6 at 70*. I am not sure if this means anything to anyone, but it is interesting.

 

Hello ! its to see if theres an open in the winding ! just set your vom at resistance setting like a 100k , hold the leads together it should read zero ! then put a lead on each terminal of the clutch coil , it should read zero or close to it . if it doesnt read anything , there is an open in the winding ! you can also run power to the clutch coil from any 12v source and see if it engages , if it doesnt , replace it !

 

To check the clutch gap.

On the front of the compressor, the inner pulley you turned and felt the resistance of the refrigerant in the compressor the manual calls the Pressure Plate.
It's held on to the compressor shaft by the center bolt.

The pulley that the serpentine belt spins is called the Rotor. That pulley is mounted/rides on the compressor shaft and free wheels on the compressor shaft because of the bearing.

Behind the Rotor/pulley is the Stator (Coil). So when the Coil receives 12 volts, it creates a magnetic field and pulls the Pressure plate against the Rotor. Since the Pressure Plate is now connected to the Rotor, the compressor rotates.

The air gap is adjusted by shims. When you replace a Clutch or compressor, the gap needs to be verified. Normally the gap doesn't change.

So on the front of the compressor (engine off) with a feeler gage measure the gap between the inner pulley and the serpentine belt pulley. Nothing needs to be taken apart. Should take you 10 seconds.

To remove the Clutch assembly is very easy.
Slip the serpentine belt off the pulley.

You can purchase a spanner wrench (auto parts store)or figure a way to hold the Pressure Plate while you break loose the center bolt. (If you look at the Pressure Plate you'll see in a triangle shape there are 3 holes for the spanner wrench ot fit).

I was able to hold the Pressure Plate by hand and used a socket wrench and gave it a quick whack which broke the bolt loose.

Once the bolt is removed everything just slides off of the compressor shaft. If I recall there may also be a snap ring that needs to be removed. The Coil is held to the compressor by some glue.

If you determine the Clutch is bad, they are not cheap. I paid around $175 for a new one.

If you need a picture of the parts breakdown, PM me your e-mail address.

 

Hooked on Vettes: Sounds easy enough. I don't have a feeler gauge handy - have to make a trip to the store. I looked in the service manual and I see what you are talking about - I guess I did not read far enough.

I jumped the coil from a portable battery pack and I can hear it clicking so it sounds like it is working.

I also measured the resistance to ground from the coil connector and got 12ohms on one pin and 560/1160 on the other depending on which lead of the tester was used. Is this normal? I would think one side of the coil should have 0 ohms to ground. I know that the diode provides a path to ground for the back emf of the coil but shouldn't there still be 0 in one direction?

Any ideas?

 

Got a feeler gauge and the air gap is between .005 and .0065 - best I can do with the gauge I bought but it sounds in spec.

 

The gap should be .02 inches +- .006 inches
So any where between .026 and .014 inches is good.
Are you sure about your measurement?

Any ways back to checking the resistance of the coil.
I'm not sure how your wiring plug to the compressor is.
The manual's schematic doesn't show the plug at the compressor end but I know it's there.

One end of the plug has a Dark Blue wire which is the 12 volts to energize the Coil.
The other wire should be Black and is ground.

Coming from the Coil should be two Black wires.

So if you disconnect the Plug and on the end going to the Coil you should measure around 3.6 ohms across the plug.

I'm not sure which end of the plug the diode is on.
To eliminate it, you need to cut one lead to remove it from the circuit. (Resolder the lead when done testing).

So if you cut the diode lead, reconnect the plug and retest.

You said you applied 12 volts direct to the Coil and it chattered? As long as the 12 volts was applied you should of heard one clunk and the Clutch should stay engaged to the Pulley.

 

I remeasured and got .018 - I have no idea what I measured before but this sounds better and is the right part. I made sure to check the manual.

As I mentioned earlier, I measured 4.6ohms but at a mich higher temp than the Manual specs - 85-90* vs. 70* in the book. I don't know if this makes any difference but that is what I got.

When I gave the coil 12v it was steady. My clips were a little too big for the connector and did not make a good connection. I got a better pair of clips and checked again to be sure.

I clipped the diode as you said and now the compressor seems to be working fine and the air felt pretty good in the 95* temps right now.

Now the question is: where do I get a new diode? RadioShack? I'll try dissecting the mess GM made with heat shrink and glue to try to find some more info on the diode values - unless anyone can point me in the right direction

So... At least my air works again - just need to clean up the mess.

Thanks!