HVAC controls not working all the time

[subijmt]

Well after driving the car with the air on for a few days, now it's back to not working right. It sounds like the compressor is kicking on, but the air is blowing hot, and I mean HOT. It is to the point of almost burning my hand if I leave it in front of the vent. I had gotten the a/c charged right before I tried the soldering bit.

[head2wind]

Check to verify that your compressor is running for sure... if it is and it has not lost its charge already from a major leak, see if one of the lines is cool/cold to touch coming off the compressor. Also, as I am writing this it becomes natural to assume that if the compressor is running then the system pressure is OK.

I would verify that the damper motors and/or mechanical damper that the cable attaches to is working properly. The A/C may be working just fine, but the heater core may be working better!

[Subtle]

Good tips for fixing things on this thread-- how about modifying the air conditioning side.

No big deal, but when the defrost is on so is the A/C and I found it worthwhile to have the defroster blowing without this feature.

Splice in a kill-switch on the wire that activates the magnetic clutch for the compressor. Low amps so it doesn't need a relay.

I did it two days after I broke my left hand and dislocated a couple of fingers in a mountain-biking incident.

Happy with the mod, but all that activity prolly delayed the healing by a week or so.

[nicebloke]

Seems like a problem I've been having lately hasn't occurred to anyone else on this thread.

Intermittently the fan stops working, and the LED indicators and vent controls also don't work. The heater control is unaffected (at highway speeds, the small amount of air that comes through naturally can still be controlled by the heater controls.)

I'm guessing that it's whichever wire supplies power to that whole unit, but I was under the impression that the fan speed controls and the vent controls were actually electrically seperate, despite being in the same location.

[Legacy777]

Everything's part of the same electronic control unit. I'd suspect the control unit being bad.....or the wiring.

[nottofast]

Same problem with fan still and we swapped in a couple different control units that had worked perfectly in other vehicles. Also tried different fan but still searching for problem.

[afterthisnap]

I pulled my panel out today and went to town with a dollar store soldering iron.
There was only one obviously cracked pin that got new solder. The rest of the pins got hit with the iron until the factory solder reflowed and then I let them cool.

Everything seems to work great after reinstalling the unit.

I was experiencing all the same problems of the upper vents not opening, and even sometimes when they didn't the AC compressor wasn't coming on. Now the vents open or shut every time and the AC is definitely rockin' when I want it to.
Thanks for the info. I would have never have found out about the repair if it wasn't for this board.

[Legacy777]

Glad this helped. I know it drove me nuts for a while as well!

[91Beater]

Symptoms:
Defrost button on far right never worked.
A/C activation was intermittent and often required hitting the button hard.
Pulled the dash out. Wiggling the cable caused the A/C relay to chatter.
Vent direction selection didn't work consistently.

All was due to hairline fracture in solder joints where switches mount on main board and the connector mount on sub board. The hairline fractures are VERY hard to see. You couldn't tell if it's just a bit of dust or a fracture. The problems are temperature and vibration dependent.

If you get a working used one, you risk relapse. So, either buy new at dealer for 1/3 of what the car is worth.. or redo all the solder connections. If existing solder doesn't flow well when you melt it, you need remove it and redo it like I did on mine.

Mine had a bunch of hairline fractures. There are seven switches and they're all DPDT designed to throw center one way when its up and center the other way when its down. The adjacent switch is dependent on the next switch being up and throwing the center to off position, so its important that every switch is properly working.

The obvious ones should be unsoldered, then resoldered. 63 tin/37 lead electronic should be used. Anything else increases difficulty.

Recommended co-maintenance: replace both back light bulbs, as well as back light in instrument cluster while you have the center trim out. Remove speedometer at transmission end for stress free cable removal. Lube shaft while you have it out.

[FundamentalyConfused]

Has anyone repaired a set of manual HVAC controls that don't look like the ones Josh did?

I have already done the soldering trick on the HVAC control that came with my car but I broke the retaining tabs on the sides of it so I wanted to replace the thing if it started acting up again. Well it's acting up again.

I pulled another HVAC unit out of a 91 Legacy wagon and the backside of it is different than my 90 sedan. The faces of them are exactly the same but there's no secondary circuit board that's attached by ribbon cable on the donor unit.

Was there a revision of the circuit board design at some point? I'm fairly sure I can use this unit but I wont know for sure if the plugs are the same until I pull out the old one. From my examination I will have to touch up some of the soldering, more than likely I'll hit all the ones I can reach just so I wont have to tear it apart again.

[FundamentalyConfused]

So I found out the hard way that the newer HVAC unit I pulled does not have the same plug that my car has. My car has a yellow plug and the newer unit has a black plug and is set farther to the side than the yellow plug.

So I hurried up and soldered the old unit and I have my defrost setting back now!!

What a waste of a junkyard trip.

[Legacy777]

Yes, there is a difference. There's a note in the parts book about it. Here's a excerpt from page 820

http://www.main.experiencetherave.com/s ... r_diff.jpg

[djshimon]

This thread has been around a long time!
I have a new-to-me 1990 legacy wagon and having the HVAC troubles. The defroster works and so do the hot/cold controls-but then it won't switch to foot or vent. I tried to solder(twice) the pins but only on the secondary/smaller board that is connected to the main board and no change. Is it necessary to solder the main board pins too? I guess I need a magnifying glass to see the cracks properly.
Thanks, aaron.

[Legacy777]

Welcome to the BBS Aaron.

Yeah you need to look at the board and see which pins may be cracked. I don't recall which ones were cracked for me, but yeah get a magnifying glass to look closely over the board.

[djshimon]

Ok I will do that.
Thanks Josh and everyone for this forum. I've already learned a few good tricks.
And Happy New Year!
-aaron

[Legacy777]

You're welcome Aaron! Let us know what you find out.

[djshimon]

Still stuck on defrost-which is the best default option. I pulled an HVAC unit(1990 legacy which is what I have) from the junkyard and tested it before I pulled it apart and soldered it and same. I still haven't looked with a magnifying glass but I soldered every single solder point on both boards(of the J/y unit) and it's still stuck on defrost or nothing- no matter which button I press. The only thing that is different about the J/Y unit is the number on it-100- whereas my original and yours in the picture are both 040...
I read somewhere that sometimes a vacuum leak could be a problem but I don't hear the internals moving between the different selections except to go to Off or back On(any button defaults to defrost).
Is there a way to manually change it?
Will a 1992-4 unit work with 1990? I am almost doubting it's the unit though. Although for everyone else it seems the only possibility.
Thanks again,
aaron

p.s. I can almost take the dash apart with my eyes closed now

[Legacy777]

Hmm.

The 100 unit is one that does not have AC, so it may not work with a chassis that is setup for AC.....or it may just not have AC. The parts book is showing that for the 90 MY, you need to use the 040 unit. The 91-94 models won't work.

If you've tried multiple HVAC units, it may be the mode selector motor or wiring. You can d/l the wiring diagrams for the 90 Legacy from me and check the wiring from the HVAC unit to the mode selector and make sure it's good. Also, I'd check the mode selector motor as well.

http://www.main.experiencetherave.com/s ... agrams.zip

[djshimon]

Thanks for that wiring diagram. I'll try and hit all the points on the 040 once more just for good measure. Is the mode selector motor under the glove box in a deep dark place? That's where it sounds like it is.
Thanks for all your help. I know it's kind of a petty problem, at least I have heat and defrost.

[Legacy777]

No the mode selector is going to be directly behind the center of the dash. If you look up at the black HVAC box from the driver's side foot well, you should see the levers. Follow those to see where the motor is located.

[djshimon]

So my feet were getting really cold while my head was hot...I manually moved the controls to floor and defrost and it was great-that was a few days ago. Today I noticed the vents were on so I pressed the defrost/floor button and it switched!!! I can only guess that moving it by hand loosened up something that was stuck? I keep pressing the controls and they keep moving between floor, defrost, and vent-like they're supposed to! Pretty awesome. I hope it keeps on working.
Only other thing-the 100 unit came out of a 1990(so it was labeled at the junkyard) and has a/c. I don't know, but I'm using the original one from my car-040-that I resoldered.
Thanks for all the help and the forum.

[Legacy777]

Well glad to hear it's working!

[justin the subie]

been reading n reading.. anyone have everything work but the 123 on the fan switch??? fan only works at 4.. full blast.. tried another unit and same thing... relay? where is it?

[FundamentalyConfused]

I would guess there's some blown resistors on the blower motor. That's separate from the HVAC unit.

My wifes van, it's a chevy venture, doesn't have the #5 setting and it's from a blown resistor.

I couldn't tell you where on the motor it would be but the blower motor is directly behind the glove box. Take out the glove box and you should be able to manage the fix I would imagine.

Good luck.

[Legacy777]

Yup, blower motor resistor. Check out this thread

http://bbs.legacycentral.org/viewtopic.php?f=10&t=1741

Here's a pic of the resistor pack. Just remove the glove box, electrical connector, and two screws holding it into the evaporator box.

http://www.main.experiencetherave.com/s ... P_2945.JPG