Heater fan won't work on HI.

[chevydog66]

I have changed the switch, fan, and all the wiring in the truck. What would cause the heater/ac fan to not work on hi. All other speeds work.

[PanelDeland]

Did you change out the resistor.It's usually under the dash on pass side.

[chevydog66]

I was going to but the one I ordered from Classic Parts of America didn't fit in the original holes so I sent it back to them. It worked before I changed to all the new stuff.

[Evaded]

This is funny.. I just posted the exact same thing a few days ago except about no hi when AC is on. Good luck to us both.

Eric

[slammed1]

Yes as already posted is most generally the blower motor resistor needing replaced. Good luck guys.

[jondancer]

You can get the resistor at most auto parts stores...
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[VetteVet]

I need to clarify some details.
Do you have Air Conditioning?
Is the fan not blowing on high with the AC off?
Is it just not blowing on high with the AC on?
Does it not work period?

Here is a diagram that shows the power to the heater switch and the wiring to the resistor and on to the fan motor. The orange wire is wired straight to the motor but is joined at the resistor. If this section of the orange wire is missing or open the high speed fan switch will be inoperative. The two other speeds can still work because they go from the fan switch to the resistor and from there to the fan through the remaining orange wire. This diagram is for the trucks without AC.



Here is a diagram of the AC circuit in the trucks with AC.



As you can see they are quite a bit different. The main power to the harness is the orange wire from the CIG terminal on the fuse box. The older trucks used a 12 ga. brown wire and may have used one instead of the orange wire.
The diagram still shows the resistor but it also shows a high speed fan relay which is not connected to the resistor like the non AC trucks.

The picture also shows a anti dieseling relay which powers the AC fan selector switch. Some trucks may not have this feature and may just run the orange or brown wire direct to the high speed relay. The high speed relay also needs to be grounded to the chassis in order for it to work.

I'm not sure if I've helped with this but maybe we can figure it out.

[chevydog66]

I have a/c but its not hooked up yet. I have a ls motor so i'm still working on that part. truck originally came with a/c. I installed a American Autowire Classic update kit in my truck last year after it was painted. I had that anti dieseling relay up by my fuse block before I stripped truck for paint. When I rewired it there was no connector for anti dieseling relay.

[davepl]

Thanks VetteVet... I'm in that situation but am wiring incrementally and hadn't hooked up the orange yet. When I did it tripped the 30A breaker I have inline with the battery cable (because I'm paranoid that way), so it's either a big draw or needs a lot of power.

Maybe the AC clutch and fan and radio take more than 30A combined?