I've got a 92 model 740T, which has had ac problems since i've had the car (about a year). Took the car to the local garage, mechanic fairly knowledgable on Volvo's he charged the system and it worked ok for a couple of weeks. Then I get no light on the ac switch and the compressor will not engage. Back to the mechanic, checks everything and says the ac relay which is built in the controls is bad. I replaced the climate control unit with a good one, and basically the same thing, worked for a few weeks and then failed. The compressor did not sound very healthy, really bogged the car down and let out some awful screeches a time or two. Is the compressor faulty and if so is that what's causing the climate control units/relay to fail. Second question are the climate control units repairable and if so, who repairs them? Thanks in advance and please forgive the laymen's terms as I am not a mechanic.

 

Yes usually the compressor overheats the control module and makes it go bad.

Some are repairable. All they need a is solder job on the circuit board.

 

Is there someone out there who I could send these to and what does the repair usually cost, or would I be better off trying to find a used good one. Thanks

 

I do them at the repair shop I work at.
You should be able to find someone close that would be able to do it.

Most indipendant shops know how to do it.

They will usually charge 1 to 1.5 hours labor.

 

I live in somewhat of a small town and getting a mechanic to pull a Volvo in the garage sometimes is a chore, although I believe the 4cyl 740 is not an overly complicated creature. But anyway, thanks again and if I can't find anyone in this area I may get back with you on some advice about who would be willing to do this. Thanks

 

Are you somewhat handy?
If so I could post how to do it.

 

I might possibly be handy enough, if not i've got some friends who are "handier" than I am. I've also got two of the units so we could guinea pig on one, and if it didn't work or I messed something up, no big deal. If you want to post it that would be great. I am familiar with getting the climate control unit out of the car, but from there i'd need advice. Thanks again.

 

Ok give me a day or 2 and I will post it.
I have to get the spare module I have at work and bring it home. I already repaired it but can still show how to take it apart and what usually goes bad.

BTW it is a MCC unit right?

 

A day or two or whatever will be fine. I won't need the ac for another couple of months. You lost me on MMC? Here is alink to what the thing looks like. Got one more question why I got you here, what spark plugs and gap do you reccomend in this car. Once again, 92 model 740 Turbo. Thanks again.



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Yes that is MCC.
MCC= Manual Climate control (Colors for Temp settings)
ECC= Electronic Climate Control (Numbers for temp. settings also has AUT on the module)

 

Got one more question why I got you here, what spark plugs and gap do you reccomend in this car. Once again, 92 model 740 Turbo. Thanks again

 

Alot of people use Bosch Platinums gapped at .030 Thousands.

 

Hi
I have had a similar issue with the AC in my '91 740 turbo wagon. I removed the MCC and melted the solder joints in the pics, and a few others where wires connected the board. It didn't look like any were cracked or loose. I didn't think new solder would fit on the joint without making a mess. Put the MCC back in and it still doesn't work. The compressor has recently been replaced, and I am pretty sure I have pressure, and the pressure switch has been checked and is OK. Where do I go from here?

 

New member here, only about 12 years late to the party based on the posting dates on this thread ... but I have almost exactly the same problem as otis44 and Bob Berzack. If you're still around, I would love to know how to service, or at least troubleshoot, the MCC module on my 1992 740 Turbo Wagon.

I actually have two of these modules (grabbed one from a junkyard car as an impulse buy, before I knew I might need it) and I've been all over the forums looking for a schematic or info on how to test them. Before the one in my car failed, I paid a king's ransom to our local specialty shop to have them troubleshoot & recharge the AC system. One of the things they found was that, just as reported by otis44, the #16 fuse receptacle was melted/burned and the technician had to rig up a bypass with an in-line fuse. But since then it's been working OK until now.

The first & only symptom was that the fan (blower) suddenly quit working. So I went to YouTube and the friendly folks there assured me all I needed was a new resistor stack. $38 later, still no go. So I pulled the blower out and confirmed that it works fine when connected to a 12V source.

Next step was a drop-in replacement of the MCC module with the one from the junkyard. (Certainly, no one would drive their 1992 Volvo far enough to crash it if the A/C wasn't working, right?) But I get no joy from that one, either, even though all the plugs and vacuum connections match up and I've meticulously cleaned every spade connector and pin I can find. The solder joints all looked fine but I retouched them anyway; still no go.

Now I'm stuck because I don't know which of the pins in the block connector is supposed to receive the main 12V input to the entire module (as opposed to the blower dial) nor what sort of voltage I'm supposed to be seeing at or between other points on the circuit board. Without this basic puzzle piece, I can't even determine if I have two defective modules, or if there's a problem in the wiring harness that they plug into. The middle dial, which selects the vacuum lines to open & close the dashboard & defrost vents, works fine, because if I run a jumper to the blower motor, I can direct the air wherever I want it. But I suspect the circuitry in the module isn't working because I can't select A/C or heat using the dial on the right, even when the blower is on full blast using my jumper connection.

I would be more than happy to send the extra module to someone who could diagnose and repair it. Failing that, I would give a major body part for a good schematic of the module itself (no Chilton's gibberish, please) so I can try to service it myself, or at least determine if the problem lies elsewhere. Thanks for any guidance you can provide!

Cheers,
DG

 

DG - I wish you good luck in trying to cool down. I sadly never got my AC to function and sold the car not long after that.

Bob

 

Here's a wiring diagram from a 1994 - (sorry don't have a 92) Should be similar.

Power comes from Fuse #16 on a black wire - to terminal 12 on the module and terminal 1 on the fan switch. The fan is wired by itself - it works with the key on no matter what the module is doing. (the module does turn the fan on low if the fan switch is turned off and the compressor is energized by the module) So if you don't have a fan (or a working module) go back to fuse #16 (or whatever replaced it)

95% of the modules fail the same way. Solder connections at the compressor relay on the circuit board crack and the compressor won't turn on. I have resoldered hundreds of modules to fix that. Occasionally the module is just dead - and a replacement used part is sourced to solve that.

"I can't select A/C or heat using the dial on the right," - That **** controls the blend door motor 6/27 in the diagram. Do you have power to terminal 12 on the module?

 

Wow, thank you so much! I'll investigate soon and let you know what I find.

I'm not used to reading diagrams like this; I gained a rudimentary knowledge of circuitry symbols when I applied for my Technician license to transmit on the ham band to fly R/C model aircraft 30 years ago but haven't done much with electronics since then. But it will be a fun little puzzle and I hope to locate the pot of gold soon. :-)

Cheers,
Duane

 

With your eyes follow the highlighted red 12volt path from the battery to the key switch to the fuse then to #1 connector on the fan switch and to #12 terminal on the module. That's a SB wire - SB is black I believe (yeah, black for a +12 volt wire) Verify with your test light.

For a tutorial on what those symbols mean - wiring diagrams for later Volvos can be found at volvodiag.com under the EWD online tab. Pick an older car and in the first few pages of the book - explains how to read them.

If your fan does not work - simply check power to the switch, then to the motor (on high speed bypassing the resister) - if you have 12 volts at the motor (the red/white wire) - is the ground wire connected to the body? (the ground is labeled 31/10)

Your "can't control temp" (meaning the blend door motor is not doing anything) is another problem - but there again the module is grounded at the same place (31/10) You can follow the white/black stripe ground lead from terminal 1 on the module to the resister to 31/10 on the body. Looks like 31/10 is located near the lower door hinge next to the passengers right foot (behind the panel/carpet) You could have a bad connection there preventing both the fan and the module from working.