Hi Speed Fan (A/C)

[bouncytruck]

The high speed on my heater/AC doesn't work. I've replaced the high speed relay, the resistor and just replaced the switch yesterday and it still doesn't work. What am I missing? Could it be the fan [motor] itself?

[Longhorn Man]

I'd look into the wires going to/from the relay.
If it was the motor, it'd at least TRY to go in high... or not work at all.

[Stocker]

When you move the switch to the 'high' setting, do you hear the relay operate?

[uncle]

Alot of times, the inner a/c box holes will be wallowed out not letting you get the screws tight that hold the relay ( and the ground wire for the relay) to the box. Sometimes you can put a little epoxy or some type of sealer in the hole to tighten them up.

[bouncytruck]

I can hear a click coming from the direction of the high speed relay.

[roughedup72]

Is this happening on your 72 Blazer? I just went through this with a 92 chevy G-20 van of which I posted ??? on the 88 truck section. I even went to the dealer and still had no luck. But I have some Good news For you. I just saved a ton of money by switching to gyco. NO thats not it!!. Really, Heres what I found and what mine was doing.

1st I could get 13.7 volts on all of my speeds at the fan motor, With it UNPLUGGED.
2nd I could plug it up and get the same at the fan motor except high, On high it would drop to 0 volts.
3rd I could test from the ground terminal on the fan to the body and get 13 volts while the switch was on high.
4th and heres what I finally found. I traced the red wire that runs to the high blow relay back to where it gets power. It had a terminal block where the red wire was connected, the terminal block had melted due to the fact that it wasnt completely tight, I took it apart, cleaned the ring eye connectors, used a new bolt to connect the terminal back together and then reinstalled the wires that were hooked up to it. Tried it out And BINGO!! I now have high speed on my A/C.
AND yes I went the same steps as you. I replaced everything including the fan. So theres where you're at and I hope this helps you out.

[bouncytruck]

Thanks. I'll check that out. I couldn't see how it could be the fan since it was working on the other speeds. I thinking it must be a wire issue. Everything under the dash is bone stock so I know it isn't due to hacking by a previous owner.

[roughedup72]

I hope it helps you out, I spent about three weeks looking,testing,replacing parts and lost almost the rest of my hair pulling it out and listening to my wife saying I'm not spending enough time with her, While she was saying it needed to be fixed. Go figure..I'm pretty sure you will find the same thing or close to it anyway. The wire may just be old and breaking apart. When it gets a full load on it the wire opens and current stops flowing. Good luck.