Looking for some help on this one. I've got a non-A/C '86 base 2wd pickup. Everything was working fine, but after sitting for a week in the cold, the blower stopped working on all switch settings.

I removed the relay and jumped the two big terminals. The blower motor ran on low speed when the switch is set to off. Low, med and high work as expected, but all with ignition on or off (can't have the fan running on low with the key out of the truck!). I unplugged the resistor and the blower is off when the switch is off, low and medium. High switches the blower to max, again regardless of ignition.

I've inspected all fuses, the resistor, blower motor and replaced the relay. All looks good.

Any ideas on how to fix this?

Thanks a million!

 

I’m trying to understand your process of testing as you described.

im not 100% sure when it became a thing, but if a resistor or relay goes bad in a newer truck the blower motor will only work on high, as to give the ability of defrost.

if your fuses, resistors and relays tested good, then inspect the blower is the problem.

 

Figured I'd update this thread with my solution if anyone else has the same issue in the future. I've drawn up the wiring diagram for my particular truck as it helped me figure out exactly what was going on.

Turns out the relay coil wasn't being powered. There was originally a yellow wire (turns into a black-yellow tracing it back a bit) going into the relay coil which was ignition-switched, but it was only putting out ~0.2 volts, not enough to activate the relay coil. I swapped that yellow wire for a different ignition-switched 12v source. All is well now.

Could anyone could tell me what that yellow wire that I deleted is? Is that relay supposed to get 12v to power the coil or does that coil require a different voltage?

Glad to have heat again, working outside on the truck in 9ºF wasn't ideal.