I have a 1994 Blazer and a while back I noticed that my blower motor wasn't blowing but just barely. I had left the blower switch on highand went out to check everything but nothing seemed out of the norm. I disconnected the hot wire that goes into the blower and checked it and when I reconnected it, the blower came on high, but as soon as I dropped to another speed it dropped back down to barely blowing. Put it back on high, remove and reconnect the hot wire to the blower and it comes back on. I took my multimeter out there and when the blower it barely blowing, I'm only getting about 2.5v out of the hot wire for the blower motor. I checked power going to the different resistor wires and that seems normal. It's only when everything it hooked up does it have this issue.

I have the wiring diagram for the blower system in my "Haynes" manual and have replaced the relay and the resistor and it's still acting up. I don't see why the switch itself would be causing it, but I plan on changing it too (it's only a $10 part). I don't see any other reason that it could be doing this except maybe it's grounding out somewhere but it's not blowing a fuse.

HELP!!!! Summers coming and I'm in South-west Louisiana... a.k.a. THE OVEN!

 

What kind of voltage do you get at the plug to the fan when you try the other modes on the switch? Since plugging in and unplugging the wire at the motor seems to change things, sounds like you have a problem with the blower motor itself...

 

If I disconnect the hot wire going into the blower and select any setting other than high, it's at about 2.5v. I thought the blower might be bad until I took the blower out of the mix and still had the same issue.

I'm starting to think it's a wiring issue, but not sure where too start looking.