Posted by gani on November 26, 03 at 14:39:56:
In Reply to: Pre-1999 Chevy SUV?Truck AC/HAVC Control Problem posted by Jesse on April 28, 03 at 21:50:07:
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
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Suburban -97 6.5TD, 135000 km