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My compressor clutch disengages with the engine hot.
It generally goes like this:
Start car. Turn on AC. Clutch clicks on and off repeatedly. Car actually cools if I get on the highway fast enough, but never lasts more than 5 miles before it shuts off. AC doesn't work again until the engine is cool again. When it does work, it clicks on and off until it stops working entirely.
Did some exploratory checks on the system pressure, along with a partial bleed and recharge. The previous owner had overcharged the system, but I would get partial function even in that state.
I also confirmed that I needed to do the breadclip fix when I was able to engage the clutch by pressing it with a broom handle.
After the breadclip fix, I attached my pressure valve and ran the engine.
Compressor would build to ~40lbs and then would cut off. It would drop to 20lbs and would re-engage. It would cycle on and off until the engine reach normal operating temperature. At that point it would shut down and stay off. Most annoying.
I've bled off pressure twice now. Right now max is 30lbs, but it's too damn hot to run at all.
Write ups (VolvoSpeed and Matthew's Volvo) say that the shims are the usual issue. Constant on/off suggests low pressure. Pressure valve says that pressure is good, so I'm left with some faulty sensor sensor somewhere. I can't find any good info on a probably culprit sensor - except that there may be one. There are references to two sensors, but nothing concrete
Final bit is that this is a c70 hardtop, not an s70. Engine systems are the same. Folks (aside from Klaus) rarely read/post in the c70 forum and I really need some help here.
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OK. Your pressure should fluctuate between 40psi and just under 20psi. The pressure must be above 20psi for the compressor to kick in.
From what you described, you are low on r134a. The pressostat is what turns the compressor on and off (or activates the clutch). With the AC engaged, both of the pipes going to the firewall should feel very cold. If the return pipe is warm, add more R134a until the pipe starts to get cold and sweat. Leave the blower on 3 or medium speed.
Forget the gauge. Most of them are wrong anyway. When adding the R134a, tilt the can sideways or even upside down after the first few minutes.
If you put in bread clips, did you use a feeler gauge to check the gap? Mine was at .046 inches, which worked fine until the compressor got too hot. The bread clips decreased the gap to .26 inch (pepperidge farm).
Did you glue in the bread clips? Did you look to see if they are still there?
The system will 'blow' the relief valve when the high pressure exceeds 550 psi. Your normal amount of R134a is 28 ounces, 26 if you live in one of the gulf states.
Klaus
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Always willing to listen, just not able to take direction.
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Klaus, thanks for the reply. I guess I should have posted in the c70 forum :)
Since yesterday, the compressor has refused to function at all. psi on the cheapo gauge reads 30psi. Nothing happens at all. Just blows very hot air, no clutch clicking no function at all.
I installed clips based on the broom handle diagnosis. The clips were flung out in rapid succession on the first try. I put them much more deeply in on the second try, but it looks like I've lost them again. It doesn't seem to be related to the click-on, click-off...
If critical pressure is 550 psi, then the system can take way more than I feared.
Guess the question would be... can you overcharge the system using a single can of R134a?
-----------Edit----------------
Okay apparently not. I emptied the rest of my 12oz can of R134a. ...must have been 8-10oz, since I added some yesterday and bled off the excess when I feared the pressure was in the red. Pressure never went above 40 psi with the clutch running.
After pumping new coolant into the system, the clutch kicked on and the lower pipe got quite cold. Cool air came out of the vents for a while, but eventually the clutch kicked off and stayed off.
So I'm back to where I started. Sounds like you have a similar issue. I read that there's a capacitor or somesuch on 850s that can be bypassed. I can't find an analogous part of my c70.
Any ideas of what I can do here? Could the preostat be the culprit?
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In the early spring of 2006, I prepared to get my daughter from college, just north of Columbus. Roof rack, Volvo cargo box(empty), just minimum luggage, and an AC check. The outside temp was 55F in MN and 85F in OH, so I topped off the system with 2 12oz cans the night before.
In the morning, we started to drive down the street. Something was making a death rattle in the engine bay. I pulled over and couldn't find anything wrong. We spent 2 days getting to Columbus without incedent.
When we went to pack up my daughter's junk, the car sat in the sun for 4 hours with the temp close to 85F, on asphault. All packed up, we said bye-bye to the roommates, started the car, drove 100ft, and BANG!! Something blew in the engine compartment!!
I got out and looked under the car and noticed a puddle of greenish fluid. I thought I had blown an antifreeze hose. A mechanic shop was down hill about 2 blocks away, so I coasted down and had him come to look at it. He couldn't find anything leaking!! All of the hoses looked OK. Started the engine and no problems.
I called the nearest dealer in Dublin, OH and told them I was coming by for a check. It was almost 4pm so the bays were empty. A mechanic put it up on the lift and couldn't find anything wrong, except for yellow dye all over the bottom of the engine. The compressor has a relief valve that popped. It probably put about 8 oz of liquid r134a on the pavement, which quickly evaporated.
I drove back to MN without a problem. Once home, I added some more R134a because the system was getting low again.
To shorten the story, yes, you can overfill it, but you probably will not harm anything.
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To verify the system being low, pull the wires off the pressostat and short them with a paper clip. If the AC is switched on and engine running, the clutch should kick in. If so, add r134a until both pipes get cold - but no more than that. You should hold the can at 90 degrees for a couple of minutes and then upside down to get the last of the can.
At a minimum, you want 45psi. Best fit is just over 60psi with the engine turned off. But cold pipes in and out of the firewall is ideal.
Klaus
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Always willing to listen, just not able to take direction.
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yes... that *is* fun :) I was full of fear after reading some of the warnings in the FAQ about the 700/900 series (my wife's 940 also has a bad AC)
It sounds like you think that I'm still low on coolant. If there's an emergency blow-off, then it does seem unlikely that I could wreck the system with too much R134a.
It may be notable that last year, when I got this car, the AC didn't work. Without a whole lot of research, I attempted to charge up the system and found that the low-pressure side wouldn't take and ounce of additional coolant.
I got the same performance as I've described (click-on, click-off) After doing some research, I decided that it must have been over-pressurized.
But I guess if it had, the pressure relief on the compressor would have blown.
So another thought... I've dropped about $70.00 on coolant boost kits. Midas will professionally evacuate and refill my system for ~$120. I didn't want to go that route because I feared that I needed a new pressure sensor or similar. If this really just is old/poor/too-little coolant, perhaps I should spring for the professional refill? But if I'm just a few PSI from proper function, then another can of r134a ought to do me...
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The compressor must be 'running' to add coolant. Usually, there is enough pressure in a can to trigger the pressostat and get the clutch to engage.
Just make sure that you shake the can first. Then screw the can to the line, but not too hard - just snug. Turn the handle down all the way. Engine running and AC switched on, connect the hose to the valve, and open the handle all the way up. Then turn the can sideways, the top part should get very cold if the gas is flowing. Near the end of the can, turn it upside down to get the rest. Close the can, unplug it from the car. The clutch should not be cycling at idle and both lines should be getting very cold.
Klaus
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Always willing to listen, just not able to take direction.
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That's fairly close to how I filled it yesterday. Engine running, AC and blower engaged. The clutch came on after I added an ounce or so and started clicking on and off (pressure gauge was reading between 20 and 40.
How fast the clutch should be cycling? Right now the pressure build and drops within a second or two. As I was filling the system, the intervals between the on/off increased to a several seconds, but eventually it quit coming on entirely - which has been the problem all along.
This AM, it was ~85 here. The AC ran for a solid 10 minutes, but eventually quit and wouldn't come back on. Drive home (~100 F) it clicked for a while, but I never got any cool air from the vents.
If this system was filled improperly in the past, could I just have a bunch of empty air in the system? If I release some of the pressure manually, should white coolant be the only thing coming out - or is pressurized air what should be coming out?
I still don't understand how it can run fine for a few minutes and then die. It seems to be a common issue. I think that I'm not quite understanding something fairly important.
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Your can of r134a should have emptied itself into the system. Forget your el cheapo gauge! You are under pressured, by a lot.
The bread clips need to be glued in! All purpose glue that sticks any 2 things together will work. After I lost my plastic clips, I found a sheet of aluminum on my work bench. Folded over once, it measured around .020 against a feeler gauge. So I installed one and checked the clutch gap - .026, much better than .046. I then pulled the clip out, glued it on both sides and slid it back in with the other 2. My clutch now works great after letting the glue cure for 24 hours. I tried it out today with a 1 hour run doing errands.
If you 'fill' the system with r134a, it will read around 60lbs. The system needs 40psi just to engage the clutch! The clutch will stay engaged until the compressor draws down the pressure to 17-18psi. When the clutch cycles rapidly, less than 10 seconds at idle, you do not have enough r134a.
You live in a 'hot' climate and should have 26 oz of fluid in the system.
If you go to Midas, have them check the schrader valve to make sure it is not leaking. Then let them vacuum the system and add 26 oz. But you must shim the clutch first - it's fairly easy lying down and reaching up. A large screwdriver to push in the clutch and a pair of needle nose pliers to hold the shim.
Klaus
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Always willing to listen, just not able to take direction.
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Found a thread over a Matthew's Volvo Site where someone suggested jumping the pressure sensor pigtail to keep the compressor running in order to suck in the coolant. You (Klaus) had actually suggested that too.
I did it, and the compressor started running. I was able to drain another 1 & 3/4 12oz can into the system and it started blowing cool air nicely. I restored the pressure switch and couldn't get the compressor going again until I pushed it with a broom stick. Then it sprang to life and ran for quite a while. I put the windows up and enjoyed the cool air pouring over me.
I had to "manually" start it twice this way, but both time it ran until I shut it off.
I'm guessing that the heat causes the clutch to move just far enough away to keep it from re-engaging when it gets hot...
So... gonna re-do the clip fix. All the clips were gone, so I'm going to use some adhesive this time and then give the car go in the AM.
I guess a combo of the two issues was killing the system effectively.
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R134a is colorless and odorless, I had yellow dye added to my system while looking for leaks. There should be very little to no air in the system, which is why AC shops pull a vacuum before adding new gas. The dryer/accumulator is there to collect any water vapor in the system. The dryer must be replaced if a line is disconnected for any length of time, or humid air allowed in.
The compressor stops pulling the clutch because the electromagnet requires more volts at higher temperatures. Plus, with metal expanding with heat, the gap is going to be larger. Shims are needed to bring the gap back to its original gap, due to wear and tear over the years with multiple engagements.
Go ahead and shim the 3 points on the clutch. With a feeler gauge you can check the gap between the clutch and the pulley.
Because 40 psi is when the compressor clutch engages, you really want more than that. The compressor sucks r134a out of the line and towards the condenser, that lowers the pressure. When the pressure reaches 17psi, the clutch is released because the compressor will overheat with the reduced amount of r134a.
There are times when the compressor will overheat and shut itself down, but you need to be in stop and go traffic and temps above 95F.
Klaus
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Always willing to listen, just not able to take direction.
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Cool!
Thanks for the extra information. The system worked flawlessly this AM @85F, and just as well @104 this PM. I have a short, unobstructed commute with little to no start/stop. Going to give the c70 to my wife and focus my efforts on sorting out the compressor on the 940 next.
Thanks for the info and the patience.
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If your 940 is older than 1993, it could be R12 based AC. If it hasn't been converted to R134a. The low port valve for adding R12 is larger than the valve for R134a, and the system cannot have a mix of gasses.
If it is R134a based, the same rules apply that you followed for the C70.
Have fun, and stay cool.
Klaus
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Always willing to listen, just not able to take direction.
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Thanks again, got both of 'em fixed. Both are R134a systems. Ended up replacing the compressor on the 940 with a good used one. The c70 is now exhibiting a new problem - loss of coolant. Seems to be closely related to the AC system...
I'll start a separate thread for a separate problem...
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The only common item is the radiator fan. When the AC is on the fan gets turned on.
Of course, the condenser is in front of the radiator and that will raise the radiator temp a little, but not enough to be noticable in the temp gauge.
Klaus
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1967 220 belonging to C.A. lives on
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The AC/coolant loss may have only be related in that it's really hot and the extra heat leads to extra pressure on the cooling system.
The fluid loss was somewhat aft of the firewall. I think it was exiting through the drain tube located in the vestigial drive tunnel. Clearance is so low it's hard to be clear w/o lifting the car.
Because of the difficulty in replacing the junction block, my heater hoses have been macgyvered (bypassed) for a while. I found a tiny split in the bypass hose which might have been the source of my coolant loss.
Upon removal, I found an old crack in the original junction block, which explains my rapid fluid loss back in the spring.
I restored the system properly yesterday with a new junction block. After refill, did not seem to be loosing coolant any longer. I need to check it again today. More time/testing is needed. I'm tracking multiple problems simultaneously.
Thanks for the help.
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