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A Quick Intro to Me. For the last year a.k.a. 40,000 miles that I have owned my 95 850T I can honestly say I probably read this forum once every week and a half. I’ll browse through about 85% of the post’s, what ever looks like it could be beneficial to learn from. Some people tell me I know everything about Volvo, I would say its more like 55% about Volvo and 82.3% about the 850. I’ve fixed numerous things for numerous people, and I’ve been taking things apart since I was 3. I’m going to go to school next month for either Marine Mechanics at MMI or Automotive at UTI where they have Volvo’s S.A.F.E. program, I haven’t decided yet and if anyone would like to give me there opinion on that it’s welcome. This is the first time I have ever made a post, I feel that you can learn more by watching and listening. Ill be giving a tip for the A/C problem that I had, I came up with this and have used it for over a month the only other solution for me was to rebuild or replace the compressor, so for $5 this trick has paid for itself. Now too the A\C subject.
This Will NOT work for everyone.
A/C Symptoms
A/C works fine until it gets hot out, the clutch will disengage even though it has power.
After swift acceleration A/C clutch will not reengage even though I has power.
Turning the A/C switch off for a while, then turning it back on reengages A/C for a little bit.
Basically this fix is for people whose A/C clutch has problems; I believe it has something to do with the windings inside. The thermal sensor should be bypassed along with this fix. I was having the symptoms above at the beginning of the summer, I knew that my compressor would have to be rebuilt or replaced. But I experimented with it and realized that when it disengaged, even thought it had power from the source, if the bypass cable I installed was given even a tap to the positive side of the battery, more voltage, It would reengage. Now at first I tried just connecting the compressor to the battery, and every time I got out of the car I had to disengage it, and sometimes the evaporator would freeze blocking all air from entering the car. So I went to radio shack and bought a relay I wired it to the compressor, to the positive side of the battery, and wired the switch to the power source wire of the compressor. Make sure to break the loop between the original power source and the compressor, meaning disconnect the plug on the compressor don’t just splice it in, if you do once the circuit is completed the relay wont shut off. It’s worked for me for over a month.
Basically unplug the wire to the compressor, wire the compressor side to the OUT part of the relay, and now wire the other side to the relay SWITCH side. Then wire the IN side to the positive side of the battery and clean your terminals while your there. And finally wire the ground side to any ground point on the car.
MichaellWeiss@comcast.net
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This is as you say, a "trick-fix" It will only work for a while and will cause the clutch windings to get hotter and possibly damage it.
I did this same fix over a year ago so I know. I eventually bought a used compressor with a clutch that wasn't worn out.
Measure the gap between the clutch plates. If it is in the .030 range, remove it and remove shims to get it down to .015 or less. I have my old (spare) compressor with the clutch gap at .012.
--
Tom 69-1800S, 72-1800ES, 96-850T,2000-S70 GLT-SE
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posted by
someone claiming to be marty
on
Sat Aug 13 09:17 CST 2005 [ RELATED]
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Fascinating!!
I'd be very interested in knowing a few things about the "fix" you've accomplished.
First, you mentioned that in installing your own cable, you have bypassed the thermal protection switch... are you sure that this switch wasn't behind the "hot compressor disengage" problem?
Second, you said that even with voltage on the connector, that the compressor would disengage, and that touching your own lead to the battery would cause the compressor the re-engage. That's a bit confusing.... when the car is running, the actual voltage at the battery isn't nominal battery voltage, but is the voltage that is put out by the voltage regulator. This will run somewhere between 13.6 and 14.4 volts. Do you know what the exact voltage is on the plug when the compressor disengages?
If the voltage being supplied to the compressor clutch is low for any reason, (poor wiring connections, faulty connector, burned contacts in the compressor relay, pitted contacts on the over-temp sensor, etc.), the result will be high resistance in the circuit, voltage drop across the contact in question, and reduced voltage to the clutch.
There is also the phenomenon called "hysteresis". Basically, it should require more current through the electromagnetic clutch in order to engage it, than is required to hold it in once it has engaged, due to the fact the air gap has been closed. As the temperature rises, the resistance of the clutch windings goes up, and the current therefor goes down. As the current goes down, the electromagnetic force holding the clutch in weakens, (current and magnetic force are proportional) and the clutch may release. I'm wondering if the clutch is badly worn, or if the initial gap is too large.
Not that your "fix" isn't a good one.... in fact I'm impressed by your ingenuity.... I'm just trying to figure out exactly what is happening.
By the way, have you read this?..... http://au.geocities.com/ozbrick850/aircon-keithP.html
Marty
'96 855T
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Yes the "fix" is bypassing the thermal switch, but I tried bypassing it before and it still shut off. I don't know exactly how this fix works, it just does. I came up with it after I realised the compressor didn't disengage if it was hooked to the battery, and I wanted to leave control of it to the ecc and sensors. Its worked for over a month here in NJ where today the high was 95. I do know that my clutch gap is in specs and that the problem has to do with the windings inside the clutch. All im saying is for about 8 bucks its saved me from having to buy a new compressor. And yes in time whatevers wrong with it will end up fubared sooner or later.
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I would suggest that this fix is only very slightly increasing the current to the compressor and will not last very long as the clutch wears further. I ried connecting an extra 6 volt battery in series with the clutch coil, which really pulled the clutch in and was OK until I blew up the extra battery while playing around. I was also persuaded by others on the UK Volvo Club forum that it was not a good idea. I ended up biting the bullet and adjusting the clutch gap in situ, which was not too difficult. There are various threads on the UK forum and others describing how to do it. In the one following I describe how I did the job on a V70, following instructions given in an earlier post: http://www.volvoclub.org.uk/dc/dcboard.php?az=show_mesg&forum=14&topic_id=19712&mesg_id=20007&page=
--
Graham
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