94' Astro AC/Heat blower only works on highest setting.

[old_master]

The dark blue wire carries speeds 1, 2 and 3 from the resistor to the high blower relay. With the resistor plugged in, ignition in RUN position, mode switch in HEAT position, the dark blue wire should show varying voltage depending on what position the fan switch is in. You can probe the dark blue wire at the high blower relay also, it should show the same results. If there is no voltage, the resistor is faulty.

[Funk-O-Meter]

With the key in the run position and mode switch on heater I removed the relay module and checked for voltage at the relay module wiring harness. The resistor module was still plugged in.

I only got voltage at the big red wire and the smaller orange wire. Voltage at the red wire pin was constant regardless of switch setting and voltage at the orange wire pin was only present when the blower switch was on the highest setting. No voltage was present at any of the other wires including the dark blue one.

If I measured this right then it must be the resistor pack yes?

The resistor pack looks ok visually. I pulled it out and checked for burn marks or corrosion and cleaned it. It was a little corroded but all of the parts looked intact. I suppose it could fail and it not be obvious to the lay-man? There's really no way for me to test the resistor pack with my multi-meter is there?

Let me know what you think, if you concur I'm going to order a new resistor pack module. And hopefully that'll be it. If it isn't I think it's HVAC shop time.

[old_master]

You checked the resistance of the dark blue wire from the resistor to the relay and it is good. No voltage on the dark blue wire at the relay means the resistor is faulty. You can remove the resistor and check each resistor separately if you want. You'll find that the resistor that connects to the terminal that the dark blue wire connects to is open.

[Funk-O-Meter]

Ok, I didn't have a chance to pull the resistor pack back out and check it but I went ahead and ordered another one since I don't think it can be much else. I might pull it tomorrow and hit it with the meter.


Thanks for your quick replies, your a great help. I'll keep with the updates.

[Funk-O-Meter]

New resistor module did the trick. All speeds are blowing now. Thanks so much for all your help guys. Especially Old Master. This forum and it's members are a great resource. I'm sure I'll have some more stuff to post about in the near future.

[Funk-O-Meter]

Update.......two weeks later....



I lost seeds 2 and 3. CRAP!!


I can't figure why. I had already replaced the relay. Now with a new resistor module and it works fine for a couple weeks and now just the last two speeds work. I listened to the motor under the hood and it doesn't sound like it's stuggling at all. comes right on on the last two speeds so I don't suspect it as the problem. Course now I can't be sure it's not going and took the resistor coil for those two speeds with it. I don't know, the motor seams fine. What else could cause that?

I may just leave it be. The last two speeds are all I really need being that on the first three speeds the air blows slightly anyway.


!%*&%$!

[old_master]

If the two highest speeds work, that means the relay and the resistor, (for the third speed) and all of their circuits are good. I would suspect the motor is drawing too much current and taking out the first two coils in the resistor. Those two coils resist the most current and are likely to be the first to crap out. Also check the blower motor ground connection, high resistance there would shorten the resistor and motor life. Post your results.