Heater/AC 78-79 Chev.

[aggie daddy]

I have 78 and 79 chevy 1/2 tons, both Big 10s. I bought the 79 a few months ago and I'm trying to get the few things that are wrong with it worked out. The problem I have right now has to do with the blower motor and/or controls. The AC isn't working at the moment so all I have is the heater to work with.

Problem #1: When I put the selector on any of the functions, the blower works fine on low and med, but doesn't blow at all when put on high.
Problem #2: When defroster is selected, it doesn't always divert the air to the defrost outlets, sometimes it will if you mess around with the controls. Also, the electric soleniod on the carb will hold the idle up when defrost is selected. I know it is supposed to do this for the AC functions, but is it supposed to do this on defrost? I thought defrost was just diverted heater flow.

The 78 has some similar problems if I remember correctly, but I haven't really started to get the bugs out of it yet.
If anyone can help me out I'd appreciate it.

[big1]

There is a high speed resistor located on the heater box on the firewall. It is probably burned out.
As for the high speed idle. The factory made that function so the A/C unit would momentarily come on even without the A/C being used. In this way it would keep the compressor seal's lubed during those long winter month's.

[aggie daddy]

Thanks for the reply. I fixed it on both trucks yesterday. I cleaned the contacts on the switching mechanism located on the heater/AC box under under the hood (I had to pop the metal cover off of it, but it snaps right back on). I don't think it is the resistor you are talking about, this is actually an electromagnet type switch. It seems that it gets corroded or dirty on the high speed contacts. Quick fix with some fine sand paper and it works great now. I hope this can help someone out.