AZ455

Hey guys,

Thought someone here might know the best place to start looking based on the symptom.

My blower runs on what sounds like low as soon as the key is in the ON position. Regardless of what I select on the fan control it stays the same speed, even in the off position. I only feel a small amount of air coming form the center floor vent.

Sound familiar to anyone?

Thanks.

MDchanic

Year and model would be helpful, but, in general, the blower is designed to run on Low all the time. Some models have a thermal cut out that shuts it off if coolant is below 40°.

- Eric

CQR

Gm was notorious for doing this in the 70s and early 80's They thought by keeping the fan running it would create a positive pressure in the passenger compartment and thus not allow any exhaust fumes to enter. (this is what I was told by my A/C instructor in school) sounds plausible. I do remember as a kid our 76 cutlass S did that.

AZ455

Year and model are in my signature.

So that sounds normal then. Well I guess now I just need to find out why the other blower settings are not functional.

fjross

Try tapping the blower relay on the firewall to see if the contacts are stuck?????

Rickman48

Those relays are notorious for going bad after 30+ years, or the connections burning up.

MDchanic

Yeah, I see it now, but unfortunately that stuff doesn't show up in the mobile version (which I was using at work).

I won't get too detailed here, but, essentially, the way the system works is that power flows from the "Heat A/C" fuse to the A/C controls, goes through the speed switch (one wire bypasses the switch to give you the "always on" effect), and comes out on one of four wires, depending on speed selected.

These wires go to the resistor block on the fiberglass evaporator box in the engine compartment, except for the "High" wire, which goes to the "High speed" relay on the side of the fiberglass box.

All of the lower-speed wires go through the resistor block and then through the "High speed" relay, to the motor.

The "High" wire activates the "High speed" relay, which switches from the resistor block wire to a separate wire that comes directly from the horn relay terminal, and connects that wire directly to the blower motor (there is a second fuse in that direct wire, for the high speed only).

So, the question is, exactly what works and what doesn't?

If only the "High" speed is bad, it could be the switch, wire, fuse, or relay.
If all the lower speeds are bad, it could be the switch, wiring to the resistor block, the resistor block, wire from thee to the relay, or the relay.
If one or two lower speeds are bad, it is probably the resistor block.

You've got to use your wiring diagram (in the A/C section, not the regular diagram), follow it out, test the connections as you go, and find the bad spot.

Clear as mud?



- Eirc

AZ455

Ah ok, I haven't used the mobile version.

I'll go through and start testing everything one of these days (before the weather gets cold again).

As for what works and what doesn't, none of the speeds work, and the horn doesn't work. Which gets me thinkin now that you mentioned the wire coming from the horn relay terminal.

Thanks.

MDchanic

Okay, so if the lowest "always-on" speed works, but NONE of the higher speeds work, then I would look at the plug on the back of the speed switch or the speed swich itself (and maybe the resistor block, but probably not).

The switch can be carefully disassembled, if necessary, but DO NOT mix up the direction of the various parts.

- Eric