94' Grand prix blower works all speeds except high.

[strippedout]

Hey gang, while replacing the old (manufactured in 96') pioneer headunit in gf's 94' Grand Prix with something more modern today, I decided to check out a longstanding issue. The blower works on speeds 1,2, and 3, but not on 4. After probing around with the old multimeter, it kind of seems like those speeds go through the resistor, but the full power High speed bypasses it. I suspect either the relay or the switch, but I no longer have access to any kind of repair manuals since I quit being a car mechanic. I was hoping someone else had the same issue at some point or could post up the wiring diagram for the hvac system, it's just the standard hvac control head, not the digital one.

[carkhz316]

Have you tested the relay or swapped for a known good one? While it could be the wire for it, it's very symptomatic of the relay itself given those conditions.

[strippedout]

Have you tested the relay or swapped for a known good one? While it could be the wire for it, it's very symptomatic of the relay itself given those conditions.

 

Well I feel kind of dumb now, I figured out the problem was a fuse, the one marked 'blower motor' specifically.

I could hear the relay click when I turned the hvac to 4, so I started looking at the diagram on the side of the relay.

when you use speeds 1-3 the relay is closed, it sends power through the switch, then through the appropriate chain of resistors to step down the voltage, then through the relay to the blower. when you select 4 it clicks the relay to the 2nd pole, which provides a separate 12v fused power source. This is strange to me since they could have just added a non resistance path to the resistor, like 99% of other blower resistors. Instead there are about 4 hvac fuses in the fuse panel. Oh well, at least it was a free fix.

 

Thanks for your help.