Wierd Issue

[VeeTwin60]

I just noticed the other day that whenever I have my AC/Heat fan on high in the cab, the engine idles higher.  I guess there are three or four fan speeds for the heat, and it only does this on the top one.

Any ideas?

[77c15]

The "high" speed bypasses the blower resistor and gives direct 12v to the blower motor. The resistor just knocks the voltage down to the other fan speeds, for example med.high is 9v, med. is 6v, and low is 3v. I would check the wires going to the resistor and the main power wire that bypasses the resistor in "high". Also, check your ground wire on the blower motor and harness. It sounds like an electrical issue, possibly in the harness, battery, or alternator. Hope this helps!

[VileZambonie]

You have a fast idle solenoid on the carb I take it?

[VeeTwin60]

I'm not sure... what do I look for?

[77c15]

A fast idle solenoid is on or near your factory rochester carb and keeps it idled up until the engine gets warm and then takes it "off" of fast idle once it warms up. I spliced into this wire on my 74's new harness to hook up the new edelbrock carb's electric choke hot wire, and it worked exactly as it should.

[VeeTwin60]

I feel dumb - after your explanation, I figured it out.

Anyway, I have a Holley, and it does not have a fast idle solenoid... it doesn't even have a dad-gum electric choke or cable for the manual choke.

[VileZambonie]

Check your ignition coil. When you put the heater fan on high the alternator output is increased, if your coil is weak the increased output can effect the firing voltage of the coil.