blower motor/switch/relay?

[k20]

Alrighty, its been chilly the past few mornings, so been runnin the heat. Anyway, Ive noticed that of the 4 fan positions, the third one up (closest to HI), doesnt flow any air. It like shuts off the fan, Lo, BARELY moves any air, one up from it moves an ok amount, next one up nothing, and then HI is beasting air everywhere.

Does this sound like a fan, a switch, or the little relay on the heater/AC box? How can I go about diagnosing which part? Money is a little tight, so I dont want to replace the fan when its fine.

 

[cbbr]

Plug the fan in directly to the battery - long wire (redneck extansion cord). If it works, test light the relay with the same wire. You are left with the switch.

 

[fireplug]

On my last truck the switch lost it's notchiness? that is the individual settings but it operated fine. Then after some time, like you, I only had high and low, so I assumed the switch had finally given up the ghost. Changed it and still had the problem. I ended up changing the motor too, and that didn't help either, so I think it must have been a relay. Where? No idea.

 

[diesel4me]

have A/C???

Only trucks with A/C will have a Blower relay for high speed on the fan..(73-87 trucks anyway..I'm not familiar with newer ones)...All trucks with or without A/C have a resistor to get the speeds other than "hi"..sounds like yours is working,or you wouldn't be getting "lo" or "medium" speed..I bet you have an A/C equipped truck,and the high speed blower relay is shot..its usually mounted close to the heater box under the hood..a bad switch could be the culprit too,as already suggested..they dont fail very often though..

 

[greg mgm]

My 78 did the same thing. On the AC box (by the blower- going by memory here) There's a panel that can be removed. It has resisters mounted to it, but they look like springs. They vary in thickness for the different blower speeds. On mine, one of them was broken, and I was able to buy a new one from a local auto store. At least check out the one on your truck, it wont cost a dime to look.

 

[dyeager535]

High speed relay would be for high only though, no? (I'm fairly unfamiliar with the AC setups)

Since it works on high and lower speeds, that would seem to point away from the relay, right? (working through the process "verbally" here)

The resistor has a coil for each speed except I believe high (based on non-AC setups) so I'd think it possible for one of the coils to be broken.

As I see it, you've got a switch problem, a wiring problem for that speed, or a bad resistor.

Easy to pull the resistor setup, if that's damaged it would be obvious when pulled, but the wiring/switch is a bit of a pain to get to, have to remove the dash bezel.

 

[nemesis_pyros]

I had a simular problem for a while on my non A/C Jimmy. I changed the switch and it worked ok for a while. Then it did the same thing again. It turned out that the po had spliced the hot wire to the switch 3 times one of the splices was only connected by 2 or 3 strands of the wire . I fixed up all those splices, cleaned and bent the contacts on the switch/plug for a better connection and now its working great. I'll never know why the po did the things he did but it just seems like a stupid idea to take power for the radio from the heater switch when the factory wire is right there.