A/C Charging Question

[CadillacFlashback]

Trying to get the A/C going on my '71 CDV.  It is still R12.  I have experience with R12 systems but have not run in to this.

I vacuumed the system down a couple weeks ago and held it on vacuum for a week.  No loss of pressure.  Today I went to add R12 and see if I can get it running, previous owner claims it worked last summer.

When I hooked manifold gauges back up, vacuum still present...good sign.  Started engine and began adding Freon.  Took the first can in fine, pressure up to about 90, both low and high side match.  Hooked up second can...won't suck it in.  Unhooked the can and opened the manifold valve slightly, it is blowing out the low side.  High side valve is not open.  12v is present at the compressor clutch but it never engaged.

Ideas?  Perhaps a bad compressor clutch that won't let it engage?   

Thanks

[TJ Hopland]

You are reading that 12v at the clutch connector?   Or is one of your meter leads on a ground somewhere else?   I think the ground for the clutch ends up around the ignition coil area.    Other thing is a meter does not take much 'power' to run so you could be getting 12v but if you really try to run something with it there is a bad connection somewhere that won't let it through.   You can either try a larger load like say a light bulb or run another power source to the clutch coil.    What does the clutch coil 'ohm out' to?

[bcroe]

Check the clutch for continuity.  Some also have a pressure switch to ground which
could be a problem, check it out.  The clutch can be replaced without disturbing the
gas charge.  Bruce Roe

[CadillacFlashback]

You are reading that 12v at the clutch connector?   Or is one of your meter leads on a ground somewhere else?   I think the ground for the clutch ends up around the ignition coil area.    Other thing is a meter does not take much 'power' to run so you could be getting 12v but if you really try to run something with it there is a bad connection somewhere that won't let it through.   You can either try a larger load like say a light bulb or run another power source to the clutch coil.    What does the clutch coil 'ohm out' to?

Reading 12v with both leads of the multimeter on the two sides on the clutch switch, so feed and ground both good.

[CadillacFlashback]

Additional observation...with the A/C system off, the face of the pulley visible behind the clutch plate does not spin.  When the A/C system is turned on, that pulley begins to spin, but the clutch plate does not.  Does this indicate anything?

[TJ Hopland]

Face of the pulley?  Its been a while since I took one of those apart but I don't remember there being that many pieces in there.   I kinda remember it being the coil the pulley with the bearing in it then the plate which is what you see on the front. 

[CadillacFlashback]

Face of the pulley?  Its been a while since I took one of those apart but I don't remember there being that many pieces in there.   I kinda remember it being the coil the pulley with the bearing in it then the plate which is what you see on the front.

Does the thick plate on the front not spin when the compressor is engaged?

There is definitely a difference in activity at the front of the compressor whether the system is turned off or on, but the thick front plate is not spinning.  Im used to seeing those spin when the clutch engages the compressor.  Am I wrong?

[TJ Hopland]

When its engaged and working properly everything you see in front of the pulley should be turning at the same speed as the pulley.

If you grab that front part (with the engine off) can you turn it by hand?   You should be able to.   I wonder if the compressor is sized and the clutch surfaces are just that burnt up that you are not getting any smoke or noise.   It usually takes a fairly good strong grip but you should be able to turn it. 

[CadillacFlashback]

When its engaged and working properly everything you see in front of the pulley should be turning at the same speed as the pulley.

If you grab that front part (with the engine off) can you turn it by hand?   You should be able to.   I wonder if the compressor is sized and the clutch surfaces are just that burnt up that you are not getting any smoke or noise.   It usually takes a fairly good strong grip but you should be able to turn it.

It turns fine and feels like other compressors I've dealt with.  I can feel the pistons moving inside as I turn it.

[CadillacFlashback]

Where's the low pressure switch on this car?

[TJ Hopland]

If you are getting full 12v and ground at the clutch terminals I don't think its a switch problem.   I wonder if it did size at some point and burn up the clutch but after it cooled it unstuck itself?

These did not have a low pressure switch like newer stuff does.   They had the thermal fuse and 'super heat' switch.   The superheat switch was basically a low pressure switch but instead of being directly in the clutch circuit it operates a heater in the thermal fuse assembly.   If the superheat contacts are activated (due to low pressure) it grounds the lead wire which then starts the heater heating.  If it heats for long enough it blows the fuse in the assembly which is what powers the clutch.   The reason for the heater arrangement was for a time delay to act as a buffer because it was normal for there to be short periods of low pressure and they didn't want the clutch to disengage every time that happened.  The thermal fuse is in the top of the AC box under the hood on the firewall.   The superheat switch is on the back of the compressor.

 

[CadillacFlashback]

If you are getting full 12v and ground at the clutch terminals I don't think its a switch problem.   I wonder if it did size at some point and burn up the clutch but after it cooled it unstuck itself?

These did not have a low pressure switch like newer stuff does.   They had the thermal fuse and 'super heat' switch.   The superheat switch was basically a low pressure switch but instead of being directly in the clutch circuit it operates a heater in the thermal fuse assembly.   If the superheat contacts are activated (due to low pressure) it grounds the lead wire which then starts the heater heating.  If it heats for long enough it blows the fuse in the assembly which is what powers the clutch.   The reason for the heater arrangement was for a time delay to act as a buffer because it was normal for there to be short periods of low pressure and they didn't want the clutch to disengage every time that happened.  The thermal fuse is in the top of the AC box under the hood on the firewall.   The superheat switch is on the back of the compressor.

I am assuming if this thermal fuse was blown there would be no 12v at the compressor, correct?

[The Tassie Devil(le)]

Yes, the idea of the Thermal Fuse is to sane the Compressor from destroying itself when the internal refrigerant pressure falls due to a leak.    Only Cadillac had these I believe.

Bruce.

[Scot Minesinger]

The thermal fuse could be bad, you can jump it out to charge the system, that is a common cause for clutch not pulling in.  Don't leave the jumper in after it is charged, because the fuse does save the compressor if charge is low.  You can buy a new fuse for about $6 from USA Parts, I would buy a couple of them.

The fuse is up on the evap casing near passenger side hood hinge, a little three prong plastic rectangle (say 1.25" x .05" x 0.75" something like that, black with small green or whit text on it) held in with a 5/16" hex screw.  Look on wiring diagram and follow compressor 12V back to fire wall and you will see the fuse wiring-that is how I first discovered it a while ago.  It is kind of difficult (likely intentional) to jump.

To test the clutch take a negative and positive lead direct from the battery and hook it to the compressor clutch.  there will be no controls in between battery and clutch.  Start the car and you should be able to finish adding the near 4 lbs (might be 3.75) of R12.  If clutch does not pull in, then it is likely bad.  Never seen a bad clutch, it is likely the fuse.

Enjoy your Cadillac!

["Cadillac Kid" Greg Surfas 15364]

Point of reference, the superheat switch in the rear of the compressor senses exactly that.  If the temperature of the return gas (to the compressor) is more than 25 degrees warmer than the pressure would indicate (superheated) the switch (in the compressor) closes, grounding the lead (at the compressor) that goes to a terminal on the thermal element mounted on the heater box at the firewall.  This closes a circuit through a heating element and after a very short time the main circuit to the compressor clutch is opened, again as has been said above to save the compressor which run under the conditions of high superheat (usually meaning short of refrigerant and thus oil) would be soon damaged.
Thermal elements were used in several manufacturer's systems, not just Cadillacs, and they are available at (probably) all auto parts stores for about $3.00.
Since it seems the compressor quit running while in the early stages of charging chances are good that either the wire came off the back of the compressor and grounded (thus simulating high superheat to the thermal element), the thermal element went because of high superheat, or if this is a car that has had the compressor turned off and back on while at speed frequently, the magnetic coil operating the clutch may have failed.
Greg Surfas

[CadillacFlashback]

The thermal fuse could be bad, you can jump it out to charge the system, that is a common cause for clutch not pulling in.  Don't leave the jumper in after it is charged, because the fuse does save the compressor if charge is low.  You can buy a new fuse for about $6 from USA Parts, I would buy a couple of them.

The fuse is up on the evap casing near passenger side hood hinge, a little three prong plastic rectangle (say 1.25" x .05" x 0.75" something like that, black with small green or whit text on it) held in with a 5/16" hex screw.  Look on wiring diagram and follow compressor 12V back to fire wall and you will see the fuse wiring-that is how I first discovered it a while ago.  It is kind of difficult (likely intentional) to jump.

To test the clutch take a negative and positive lead direct from the battery and hook it to the compressor clutch.  there will be no controls in between battery and clutch.  Start the car and you should be able to finish adding the near 4 lbs (might be 3.75) of R12.  If clutch does not pull in, then it is likely bad.  Never seen a bad clutch, it is likely the fuse.

Enjoy your Cadillac!

I cannot see anything that matches your description of the fuse around the evaporator casing.  Regardless, it may not matter:

I ran jumpers from battery to compressor clutch.  I get the same results when hooked to the jumpers as I do the regular harness wiring...when the A/C is turned on, the "clutch plate" as identified in the service manual (thin plate in between the thick clutch assembly on the front and the pulley where the belts turn) spins.  The "clutch assembly" as identified in the service manual (the thick plate on the front) does not move. 

Something is happening when the A/C is turned on, just not the right thing.  I am assuming this means the clutch is shot. 

Can the clutch be removed with the compressor on the car?

[Scot Minesinger]

Sounds like compressor clutch and maybe compressor is bad.  Clutch change out is difficult, and you run the risk of compressor being no good with a replacement clutch.  I would replace both.  Also at a minimum I would replace the dryer too in front of condenser, because if compressor did fail pieces of it may be in the dryer.  I think the double belt compressor/clutch assemblies are around $450 rebuilt. 

It may be a good idea to clean up the POA internally while system is apart.  Sometimes those malfunction, and can be made to operate again without replacing.  If a/c really did work last year it might be OK.  The downside risk is if it is not, then you have to recover the R12 and make repairs, as opposed to now when it is much easier to deal with.

Further, the hoses and O rings should be replaced too if you plan to keep the car a while.  Those hoses can last a while. If you just need a/c for the summer or a few years, the hoses may be OK.

You will need to recover the can of R12 in the system now.  Do not vent it to atmosphere, or risk 25k epa fine.

The fuse could be bad too, and I would get one because they are inexpensive and necessary.

["Cadillac Kid" Greg Surfas 15364]

Scott (F),
Yes the clutch can be removed with the compressor still attached to the system.  It is easier if you un bolt the compressor from the engine (two bolts in the front bracket and 3 bolts in the rear compressor bracket) and lift the compressor up where you can access the front end easily. It does take a couple of special tools to pull the clutch plate and the compressor pulley, but it is possible.  I still do not understand your situation.  I understand the front clutch plate does not move regardless of what you do, but exactly what changes.  The pulley/clutch assembly consists of (in your case) a double groove pulley that fits on the nose of the compressor with a magnetic coil underneath, and the clutch plate.  When the coil is energized (the two connections at the front of the compressor just behind the pulley) is pulled to the rear to contact the face of the pulley, engaging the compressor.
IF you see anything change when you apply 12 volts to the coil it may be that the clutch is not corre4ctly adjusted. Let us know
Greg Surfras

[Glen]

I had a problem with the A/C clutch on a 88 Chevy, the power was at the connector but the clutch would not always engage and turn the compressor.  I bought a new clutch coil and as I started to remove the clutch I found the nut in the center was loose.  I tightened the nut and the compressor ran fine after that. 

Check the nut in the center of the clutch on the end of the shaft. 

["Cadillac Kid" Greg Surfas 15364]

Glen,
The clutch on an A-6 is keyed on the shaft. 
Greg Surfas