Jari: A/C controls are in hand. Now what?

[DickWells]

Hi Jari: I have the heater/A/C controls out of my 95 Sub. and it looks like the circuit board may not be the same as yours. There are four transistors on the board. (if I'm actually recognizing a transistor) They are little black, half round things with three legs. Three of these have different numbers. And there is no indication on the transistor or on the board as to what their function is. (no location indicated for the pins as you described)
As you can see, I'm in a little bit of a bind now, what with the dash all torn appart, and no idea what to do with this little circuit board. I can get arround OK, I think, but it would be nice to have this thing fixed.
Hope you can enlighten me.
Thanks, Dick Wells.

[markrinker]

Dick -

I bought two controllers for my 1994's - as things seem to fail in pairs for me! Not sure if they work on '95s, the spare cost me $85.

If you want to buy it, let me know.

[96ccdd]

This is from a post I saved to fix my 96, hope it helps.
Mark
Hi there!
I hope this info is valuable to someone perplexed by defect a/c.

If you have following symptoms in your truck
1) A/C button won't work
2) Recirc won't work
3) Mode of operation knob has no effect (air comes only to floor for example)
4) Rear defog button works normally
5) Temp and fan speed knobs works normally
then you might have a similar problem I had. The fix is both easy and inexpensive. Culprit is bad transistor Q1 on your control head. By changing it (cost: 6 cents at Radioshack) everything works as usual. Here in Finland GM dealer asks 275 Eur (about same in US dollars) for the head, so there is your motivation to fix it by yourself.

To take the head off, remove dash and gently slide the head out. There are clips on both sides of the head, you need a screwdriver to tweak them slightly inwards. Disconnect all cables.

The transistor is MPSA56 (bipolar pnp) and you can locate the faulty one easily. It is the one under the bracket just next to mode of operation knob axis (NOT the easiest one at the edge of the board). Install the new one to the other side of the board, so you don't have to fit it into that extremely confined space. Make sure to connect the legs to the right holes. Emitter, base and collector are marked on the faulty transistor.

If you have anything to ask, contact me and I'll send more descriptive instructions.

jari

[DickWells]

Thanks to both Marks for responding.
I may be on the road to recovery. ? Got a new transistor today which is a direct replacement for the number that Jari from Europe referenced. I didn't have the courage to try to get it in tonight, so I'll do it tomorrow. Besides, after
being in there for 9 years, I think it's time to put new bulbs in there while I have everything out. I have a great opportunity to freshen up all the grounds under the dash, too.
I hope I didn't throw you off too much by posting a new note to get near the front of the Forum. It all started when I read Jari's note from back on 02/12. I haven't heard back from him yet. It's been almost 30 years since I worked on anything where I had to replace a transistor, so I have to admit that I couldn't even remember how to identify one!
If I get into real trouble, I'll really consider
having you send your spare down here to the camp ground, Mark.
Thanks a lot guys.
Dick Wells