I had this problem last fall, but haven't had the chance to take it to a mechanic until now - A/C compressor cuts in and out every few seconds, causes the car to "chug" as the clutch clicks back on. I'm taking the car in tomorrow, however, his over the phone diagnosis is "might be the compressor". Any ideas? I had the high and low side switches replaced last summer. I think this might be the original compressor. Thanks!

I've had the same problem the past summer -- rapid cycling, on and off.

The usual diagnosis is a low level of refridgerant. I didn't want to go through leak tests, etc., at the end of the summer when the problem arose; I've put it off until the coming spring.

It's a shame that these cars don't have a "sight glass" on the drier like the old cars did, to look for bubbles -- it seems that this rapid cycling is the only warning of low levels in these 1993s.

I recently had the same problem with my '91.

It was a low charge. The low pressure switch located on the accumulator controls the compressor.

The only place that I could find a leak was on the special Volvo fitting on the accumulator.

The valve leaked from under that big black cap.

I recovered my refrigerant down to 0 psi by putting ice around my container and letting it condense toward the cold from the high side.

Super glued a thin solid steel slug to the top of the valve and replaced the cap. Vacuumed the system briefly.

You have to recharge the system by weight noted on a decal. Because of the orifice tube metering device that is located in a line between the lower outlet of the condenser that goes towards the firewall.

Guess close with small cans or weigh them as you go.
I used a 70 lb. postal scale from Harbor Freight because I use a thirty pound jug.

Worked fine all last summer.

it might be the compressor! sounds like a leak to me. a low charge will cause the ac to cycle on/off. it could be the compressor is leaking. or, if it's locking up, then the engine would act like it's trying to stall. maybe that's what you meant "chug". good luck, chuck.

Hello,

Ran my AC this morning, hey it was humid south of I10 OK! Supposed to be in 40's on the way home. 4 inches of snow Wednesday night, mid 70's yesterday, 68 this AM and humid as heck, then mid 40's with a low in the 30's tonight. My sinus cavities hate me right now.

Back to the click and thunk issue, the very first thing is to hook up a set of gauges and see what your system pressures are. Sounds like you have low pressure and maybe something else going on with the compressor. But that is speculation on my part. Bottom line is to truly take the guess work out, hooker up and lets see what you got.

If you have low pressure on both sides of the compressor that would point you in the direction of adding coolant and a possible leak.

If you start adding coolant suddenly see the pressure shot up when you turn the compressor on that would point to some sort of blockage in the system. 9 out of ten times that will be the variable orifice being plugged up. If you have a good low pressure reading before the compressor kicks on and then the low shoots way up that is also a sign of blockage.

Could also be over pressured, had a buddy bring over a car last month that the compressor would make a loud noise and shut off. He had added coolant to with one of those blue fill hoses and said that had worked before. There was 120 psi on both sides of the compressor and thankfully a high pressure switch. After venting errrr I mean removing the excess coolant to bring the pressure down to the factory specs the AC started working like a champ. Made him give me the blue hose and promise to get a set of gauges or at least come by and borrow my set. Not my good set now, I have a "loaner" set from Harbor Freight that is decent for home use. He had to have added at least two or three cans to get the pressure that up that high I think, never did get a straight answer on how much.

Good Luck,

Paul

OK, the plot thickens, but we are getting someplace. My mechanic thinks it's not the A/C - that's working fine. I like his thinking because in the past 4 years I've replaced everything A/C on that puppy except the e______r. (shh, knock on wood). He thinks its loosing primary voltage at the coil, and the volts/amps required to click the A/C clutch on causes or is a symptom of the the primary voltage drop. Impulse module has so far checked out ok so far. Any ideas? Thanks!

If I read your post correctly, your pro believes that the clutch is dropping out from the controls. For that to pan out that would me a loss of voltage or current, and that causes the thunk. For his theory to work you would need inadequate voltage or current from the inside of the car or loss of either.

What are the high and low the pressure readings by the way?

I can think of four basic things that can cycle or cause loss of power at the AC clutch. They are in no particular order the low pressure switch on the dryer, a loss of power at the AC switch (the light in the switch should flicker). The thermostat circuit inside the car (cycles the compressor so the condenser coil does not freeze up. The clutch on the compressor not engaging properly or slipping. The last one can be from a bad clutch or excess pressure in the system. That is "assuming" the compressor has good bearings in it and you seem quite sure of that.

Two things could prove or disprove the theory, the first way is to take a wire and connect it to a say 20 Amp rated switch. Run the one side to the brown wire on the compressor, and with the switch in the off or Normally Open position connect the other side directly to the battery. With the engine turned off close the switch and watch the compressor clutch. If working properly it should go click and move backwards. If it does not move or the wires start getting warm turn the switch off and you have some sort of clutch issue. If it goes click and moves back great, turn off the switch and start the car. Flip the switch and you should now hear the click and the compressor should start rumbling. If you get a click and a clunk, a loud squeal with the smoke and the smell of burning rubber when you close the switch, scream "Turn IT OFF, Turn IT OFF" to the key operator, or turn off the switch. His theory would be wrong you are back at system pressure, compressor bearing or a bad clutch on the compressor. But if it starts running and there is cold air in the car the theory is correct and it is not the actual AC compressor and the cooling part of the system and give him a gold star.

If the connection of a wire direct to the battery is not your cup of tea, you could opt for the more technical approach and pull out a VOM (something manly with the chance of hot wires and if that sucker locked up when the clutch engaged the smell of burning rubber). First Measure the resistance from the Brown wire on the clutch to chassis first, do not remember the resistance but it is not a dead short. Check the voltage on the other side of the connector for +12 volts to chassis with the engine running and the AC Switch on. If working correctly you see a steady voltage that does not cycle on the pin. If if does cycle back and forth then you are headed over to the low pressure switch. Take the VOM and at the low pressure switch measure both sides of the switch to chassis. If you see a steady voltage on one side and a voltage that cycles on the other either the switch is bad or you have low system pressure. If you see the voltage cycle on an off when you measure both sides of the switch the next place to check is the thermostat control circuit inside the car (give him a gold star). It is possible that the switch that prevents the Condenser coil is having a problem and that is cycling the AC on and off. Also check things like the contacts on the fuse box for corrosion, and good clean contact surfaces.

Good Luck,

Paul

Some clarification: The symptom is - while driving down the road w/ the A/C on, the A/C clutch clicks off and then back on again (click/click)in less than a second. The car also jerks/hesitates/chugs for a split second. I thought the A/C clutch suddenly reingaging was causing the chug. However my mechanic says he was also able to cause the hesitation w/o the A/C on, therefore he thinks the hesitation may not be caused by the A/C system. I haven't noticed it happening w/o the A/C on.

His theory: another electrical problem is causing the voltage to the clutch solenoid to drop low enough to drop out the A/C system for a second.

They have checked the A/C and it is working ok. I don't know the HP/LP. The belt doesn't squeal when the clutch engages. They say they are familier w/ the Volvo A/C systems.

The VOM, thermostat control circuit and fuses are a good suggestion, also the coil. I have the car back for a few days due to the Mrs. I will try to swap a coil in there from the twin and report back. Maybe it is a bad wire. Question - if I measure voltage at the switch - do I probe the wire on either side of the switch to take the reading?
Thanks!

First of all, check your rear end the next time you see this guy. IMOH he is blowing smoke up your buttocks.

You wrote,

"Some clarification: The symptom is - while driving down the road w/ the A/C on, the A/C clutch clicks off and then back on again (click/click)in less than a second. The car also jerks/hesitates/chugs for a split second. I thought the A/C clutch suddenly reingaging was causing the chug. However my mechanic says he was also able to cause the hesitation w/o the A/C on, therefore he thinks the hesitation may not be caused by the A/C system. I haven't noticed it happening w/o the A/C on."

Is this R12 or R134 converted?

There may be a hesitation with or without the AC on, but that is caused by vacuum leaks, fuel pressure regulator, plugs and wires, and so on. Hesitation caused by the AC system when your clutch engages driving down the road rapidly like that there has got to be a pressure issue in that system. Over, under, or clogged there is something wrong inside the ac system that is causing this. The compressor does send a signal to the ECU, (well in a 86 it does anyway) that causes the Idle to increase to compensate for the higher load on the engine at idle. That has not a thing to do with the clutch dropping out affects the idle only.

If your AC cycles quickly at speed what does it do when you slow down? I will bet it does the same thing and that it does not cool at all. That is when you need a set of gauges on that compressor.

Seek professional help or go to Harbor Freight and get the set of gauges on sale. We can tell you how to hook it up and tell you what the readings seem to indicate.

Save your butt cheeks, stop smoking, and find another pro, I would highly suggest finding a real Auto AC shop not attached to any chain or in a shop with some guy who does it part time.

Good Luck,

Paul

Yow! You got to find another mechanic.

Take the car to another state. His credentials (if Florida uses them) are being purchased with your credit card! Impulse Module checked out? Must have been your wallet.

This guy is totally wrong. His is babbling and blowing smoke. Taking advantage of your desire to be cool. You got it, by saying PLOT!

That my ideas.

Please elaborate, so far he is ahead of everyone here. re impulse mod - I may have not heard him right or he may not have used the exact volvo world word for it, but he seems to be on the right track on the root cause. Regarding his credentials, they are well regarded and recommended.

I only wrote you my idea on the subject of the A/C that you started as a problem.

The things he said are not items connected to rapid cycling of the compressor. It is engaging and loading the engine.

When the A/C is cycling you should only feel the loading of the engine as it cycles.

Hesitation/jerking/chugs are more in line with what has been mention by Paul Driver of Inga. A over charged/plugged/moisture wet system.

If YOU only notice it with the A/C on was my clue that the mechanic "may" be doing "the customer dance". Guessing at what you are telling him to fit a symptom any where else. I admit, a mechanic depends a lot on the customer to tell him what needs to be fixed.

Then again you may have two problems. One exaggerates the other. The A/C changes the ECU mode. It effects idle speed. Loading effects timing.

If the A/C load or cycling is out of ECU program load perimeters, there could be symptoms of possible "shuffling" of a whole lot of the engine controls.

A mechanic in business should be all you mentioned. He should know that this is a GM A/C system. Charge weight is critical for proper operation. Orifice or capillary tube systems are charge critical.

A refrigerant leak or air and even a drop of moisture can change its pressure behavior quickly as Paul tries to put in his post.

It appears that you have been fighting that A/C system with a lot of parts changing. My thought or idea is. How Come?

Its a straight forward simple system and probably the best Volvo has used in all the years. Except the 850's on. They got leaky tubes in their evaporators that dealers ignored when ever possible!

I don't like the climate control complication. Having to adjust something is a good thing to keep you alert/awake otherwise, it drains your pockets.

Since you are on the brick board you are going in the right direction. Learning how to describe the problems with a vocabulary that you will learn by being involved in the car world around you.

Decide, A/C always or not and think with us. You'll have the fun we get in the process.

Regards!

Response to Paul, Driver of Inga:

IMOH he is blowing smoke up your buttocks.
I still think he’s a good mechanic, but it’s obvious he’s not diagnosed the problem.

Is this R12 or R134 converted?
R134 Didn’t all 93’s come w/ R134 straight from the factory?

There may be a hesitation with or without the AC on, but that is caused by vacuum leaks, fuel pressure regulator, plugs and wires, and so on.
Agreed. I drove it to work today using the A/C for part of the trip and then turning it off to compare. Runs smoother than velvet w/ the A/C off, and on (when it’s behaving).

If your AC cycles quickly at speed what does it do when you slow down? I will bet it does the same thing and that it does not cool at all. That is when you need a set of gauges on that compressor.
As noted above, I drove it w/ the A/C on for awhile. A/C works fine. I actually barely noticed the chug/hesitation this time, on a 20 minute drive it only happened twice. Maybe it was because it was only about 65 this morning, I had to have the heat running a little too (my apologies if that last comment torked anyone off) Also, note that the problem is not a regular or constant occurrence; runs fine, then chug, chug, then ok for 15-20 seconds or a minute or two, then again. Twice when slowing braking for a light I heard the compressor clutch click rapidly – click click click. Tried to make it do it again by stepping on the brake –nope.

Seek professional help or go to Harbor Freight and get the set of gauges on sale. We can tell you how to hook it up and tell you what the readings seem to indicate.
I will be looking into some gauges. I have poked my nose into ‘bout everything on these cars except A/C , tranny and under the valve cover, but I think it’s time to learn how to do the A/C repair on these, or at least get a little less clueless.

Response to Machine Man:

When the A/C is cycling you should only feel the loading of the engine as it cycles. Agreed, I do when it’s behaving.

Hesitation/jerking/chugs are more in line with what has been mention by Paul Driver of Inga. A over charged/plugged/moisture wet system.
I’m putting that at the top of my list.

If the A/C load or cycling is out of ECU program load perimeters, there could be symptoms of possible "shuffling" of a whole lot of the engine controls.
Also on my list.

A mechanic in business should be all you mentioned. He should know that this is a GM A/C system. Charge weight is critical for proper operation. Orifice or capillary tube systems are charge critical.
Agreed.

It appears that you have been fighting that A/C system with a lot of parts changing. My thought or idea is. How Come?
The evaporator had a leak. The compressor was damaged by another mechanic while changing a hose. Don’t remember about the condenser. The high and low switches were also malfunctioning. This car has some corrosion problems in the front end and a few other random areas.

Summary: I still think the A/C is causing the problem, either charge/ moisture or an electrical component in the A/C system. Next culprit is something else electrical, maybe even a bad wire.

If it is a simple case of not knowing how to properly charge the system, then I will definitely seek professional help elsewhere. That will be a shame as this shop is very convenient. They have been in business for years and have a very good reputation.

However if this is weird, hard to diagnose problem, then it’s going to take some trial and error to work through. My thanks to all for the info, I will update further.