1973 C/20 Heater and fan issues.

[Wilson1971]

I'm new here and new to ownership of my classic truck. With the key in ignition, without starting my truck, the heater fan begins to blow. It blows all the time. I have been told that this is normal, and I have been told that this is not. Which? Also, I am not sure that the truck is equipped with A/C.
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[tucsonjwt]

When you turn the ignition to the ON (not START) position the blower motor will come on at low speed (the fan switch will be in the lowest position.) This is GM's "flow thru ventilation" which is supposed to reduce the risk of any exhaust gas collecting in the cab if you have an exhaust leak, and also help reduce condensation in the cab.

If you have a/c, you can look under the hood and see the a/c compressor on the driver's side, plus the refrigerant lines going across the front of the engine to the heater box on the fire wall on the passenger side.

Search for a/c on this forum to see pictures of a/c equipped trucks. The heater control is also different on a/c equipped trucks.

[motornut]

my later trucks had a (always on)brown wire jumper at the dash switch,
drove me nuts so i cut it,lowest speed is off now.