[MASTERBrian]

I hope I'm on the correct year group for this as I realize the 99 Trucks had already switched to the 5th gen body style, yet the burbs lagged a year, so this is a 4th gen body.

This isn't a daily driver anymore so it hasn't been a priority, but I'd like to get it working right. Several years ago I had an issue with the hvac system and I replaced a few parts. It started working again, but the high speed doesn't blow and hasn't since. I just don't recall what I replaced at the time...seems like blower at that time. I know I've replaced the blower resistor and possibly even the relay, but not 100% sure on the relay.

I had someone mention maybe a bad ground to relay and/or resistor and they said if you ground it out to chassis, that's a good quick test. Problem is I don't know which wire to ground or which part. On the relay, I'm guessing it's the black wire going into the 5 wire blower motor relay???

My understanding is the resistor only comes into play for the 1-3 fan speeds and the 4 speed bypasses it. If this is correct I'm guessing I can ignore this piece. Then it seems the relay is mainly for the high speed, BUT if I unhook it, none of the speeds work....makes since, but just pointing out. As for the fan, is it possible I have the wrong blower? It's a VDO PM149 and it seems to cross just fine with my 1999 K1500 Suburban 5.7L LT.

Any ideas or suggestions where to turn?

For what it's worth the relay is a Siemens 12193601. Could it be the control unit? I also checked the wires at the blower and they seem fine....if I unhook nothing works and only two wires that I see.