A/C not working

subijmt · Post by **subijmt** » Wed Aug 02, 2006 11:23 pm

I am having problem with my a/c and am hoping that someone can offer some helpful suggestions. Whats happening is this: Obviously the a/c is not working when selected by the a/c button inside. The fan blows warm air and the compressor doesn't kick on. Now, if you unplug the harness on top of the compressor and add load to the plug directly it will kick on and blow cold air. I already checked the four relays in the engine compartment fuse box and they all have ohm loads around 104-106, and all switch with power and pass through the power. So basically the electrical signal is not reaching the comp. and am hoping someone can give me a diagram or guidance in tracking down the problem

subijmt · Post by **subijmt** » Wed Aug 02, 2006 11:27 pm

I guess I should have specified that this is on a 90' legacy L wagon w/manual

theflystyle · Post by **theflystyle** » Thu Aug 03, 2006 12:58 am

i just had my car gone for close to a week trying to find the elec problem. i was in the same boat as you and some wire(s) were either cut or corroded on my 94l.

subijmt · Post by **subijmt** » Thu Aug 03, 2006 10:48 pm

Does anybody think that it could be the contols on the inside not sending the voltage, our do you think a wire is cut somewhere?

I've searched many of the archives but can't find any a/c electrical issues covering this. I am hoping to get some kind of diagram or chart depicting how the electricity gets to the comp. because it is obviously not getting delivered there.

Post by **Legacy777** » Sat Aug 05, 2006 4:42 am

Pull the ac relays, use a test light or multi-meter. Have someone turn on the AC with the button and see if you get power at the fuse box when the button is switched on. If not, you'll have to keep going up the trail.

There's really not a good place to test the wiring directly behind the hvac unit to see if it's a wiring issue or controller issue.

subijmt · Post by **subijmt** » Sat Aug 05, 2006 8:06 pm

Thank you, I will try testing the fuse box, and then probably take the controller out of the dash and put in another used one to see if that solves anything

subijmt · Post by **subijmt** » Thu Aug 10, 2006 5:07 pm

OK? I pulled the relays and checked while the unit was selected to Max A/C and then also with it switched to Off. Both times the relay ports had power. Now the other weird part, to me maybe it makes sense to someone else, I pulled the fuse for the A/C in the same compartment and tested for power with the unit selected to Max A/C again, and again with it switched to Off. And it showed power on both sides!? Is it supposed to do that? It just doesn't seem right. Why even need a fuse there then to bridge over if there is power on both contacts?

scuzzy · Post by **scuzzy** » Fri Aug 11, 2006 5:12 pm

There is a thermocouple in the air box with the evaporator (inside the car) which measures the temperature of the evaporator fins, if this switch of sorts is defective (and they do go defective) then it will never read properly and the AC won't turn on.

subijmt · Post by **subijmt** » Mon Aug 14, 2006 7:44 pm

subijmt · Post by **subijmt** » Fri Aug 25, 2006 4:56 am

Well I figured I should post an update to see if anyone knows whats happening.

I pulled the controls out of the dash and put in a new(used) one to see if that was the problem. With the new one in I noticed that if you bumped or wiggled the wiring harness that plugs into the back yellow plug; you could hear the relays clicking on and off and the comp. would kick on. With that new bit of info I put the old one back in because the new one came from a salvage yard and it looked like it too. With the old one back in, I tried playing with the yellow plug and had to really pull up on the whole harness to make that same result. So as a temp fix as a test I wedged some pieces of plastic underneath the harness to apply constant pressure, and it seems to work better but still not as well as I would like. I can tell that the system is kicking on but only really blows colder air when I add more pressure upward on the clip..

I am interested in what you think is causing this. Is it a joint somewhere on the board, or contacts in the actually plug? Do you think that I could blow some air into the plug to try and clear any debris (dust) and then put dielectic grease on the pins before I clip the plug into place?

Post by **Legacy777** » Sun Aug 27, 2006 9:53 pm

You can try that, but don't know if it'd make much of a difference.

subijmt · Post by **subijmt** » Mon Aug 28, 2006 4:59 am

Do you have any other suggestions as to what could be wrong?

Post by **Legacy777** » Tue Aug 29, 2006 4:12 am

Not really, other then the control unit being bad....or possibly wiring.

head2wind · Post by **head2wind** » Tue Aug 29, 2006 11:56 am

Isn't this the common problem of the PCB solder joints failing on the HVAC control panel to harness plug? I had a 91 that did the same thing. I ended up doing several things: Resoldered all the joints on the sub PCB where the car interface cable plugs in and I had the AC refrigerant recharged. Since the system was below the cut out PSI it would not allow the compressor to come on. Once the system was back to above 70PSI the pressure switch reset and I was back in business.

subijmt · Post by **subijmt** » Thu Aug 31, 2006 2:14 am

I just had the system charged a few weeks back hoping that was my problem so I am pretty sure it rules that out.

So you think that since I can apply pressure upward on the yellow connector that the problem is a bad solder joint on that immediate board? Does that board come out cleanly? Do I just add solder over the existing joints?

head2wind · Post by **head2wind** » Thu Aug 31, 2006 4:15 pm

"So you think that since I can apply pressure upward on the yellow connector that the problem is a bad solder joint on that immediate board? Does that board come out cleanly? Do I just add solder over the existing joints?"

Subijmt, yes since you are torqueing the plug to achieve intermittent connectivity there is a problem within that interface area. This problem is usually the solder joints of plug on the intermediate PCB, not the connections within the plug itself. The intermediate PCB is secured to the main HVAC control panel PCB with plastic standoffs. You can remove the intermediate PCB by carefully squeezing exposed tips of the standoff pins and prying up to get it away. There is a flat cable that goes from the intermediate to the main PCB, this you will leave alone as it is not the problem, just be carefull not to damage it when removing the intermediate PCB.

Once it is away you can get to all the solder joints on the back of the plug. If you have very good eyes, a loop or a small magnifying glass you can inspect the solder joints. Most likely you will discover fractured/failed solder joins. In most cases you should be able to resolder the joints by using a 15-25 watt iron, without adding additional solder. If the PCB is dirty, wipe it off with a water dampened paper towel. If you want to make absolutely sure it is clean, go buy a small stainless wire brush and lightly brush the solder joints to remove any residual deposits, wipe with isopropal achohol, then start soldering.

If you need to add solder use the smaller gauge solder that you can get from a electronics store and just add a very small amount, just enough to freshen the joint and replace any that may have wicked to the other side of the joint. I resoldered all the joints on my unit, independent of whether or not they had failed. Once you have completed the resolder, resecure the intermediate PCB onto the standoffs and you should be all better.

With the recharge and resolder my system began to work as it should.

As a side note, I believe that I read somewhere that the 1993 and/or the 1994 version of the HVAC control head was altered/upgraded to solve this problem. There is a 93 Legacy in the local junk yard, I will have to take a look at that one to verify if it is true for the 93 or not. I will take a look at my spare 1994 HVAC control head, maybe take a picture of it, and we can compare to yours.

I hope this helps, let me know how it goes.
Ken

subijmt · Post by **subijmt** » Thu Aug 31, 2006 7:10 pm

Thank you for the great explanation, I will have a chance to get back in and try this process a little later in the day. Souds like it will work to me though.

subijmt · Post by **subijmt** » Fri Sep 01, 2006 5:41 am

Well I took it all apart and added solder to every spot on that connection, hooked it up and YAHTZEE!! It was getting dark, so tomorrow I am looking forward to putting the dash back together. Thanks again to the great write up. I was so happy it worked that I took apart the second unit that I had bought from the salvage yard and soldered it too. So now I guess I have an extra for backup.

head2wind · Post by **head2wind** » Fri Sep 01, 2006 5:47 pm

Very COOL, pun intended!

Hey, can we make this a sticky? I had to SEARCH and SEARCH to find this info and there is not any one good resource for this. Moderator, what say ya?

Oh, and I will do a complete photo and how to write up if we make it a sticky.

subijmt · Post by **subijmt** » Fri Sep 01, 2006 5:57 pm

if you need some pictures let me know, I have that extra one that I can take apart again

Post by **Legacy777** » Fri Sep 01, 2006 6:46 pm

I believe this thread that is stickied in the body & chassis forum pretty much covers the same thing.
http://bbs.legacycentral.org/viewtopic.php?t=1142

I posted pics in there of the HVAC unit, and I believe of the board you mention.

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A/C not working

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