fan blows

[Abnorml]

On my 73 Cadillac hearse the fan blows even when the fan's turned off. To add to that, the heater is not working. Need to get that fixed soon, before it gets cold.
Does anybody know how to fix it?

[hotroddwayne]

With climate control the system is trying to make the area a specific temperature. Even with the fan turned off it will still blow at a low speed trying to adjust temperature. My '80 does the same thing, the fan will run low even when the fan speed switch is off. It all depends on what you have the climate control set at vs. the actual temperature in the car. As for your heat not working... check to make sure no one has bypassed the heater core. If it's still hooked up & you definitely have hot antifreeze flowing through the heater core you'll have to experiment a little & find the linkage that controls the flap in your heater box that directs the flow of air. That internal flap door directs air either around the heater core or through it. I can't give you specifics since i never had a heater box apart in an early- mid '70's Caddy but hopefully this helps.

[Psychoholic]

There is also an 'ambient air fan' that runs all the time while the ignition is keyed hot. There are 2 wires that run to a fan next to where the heater core hoses go into the firewall. My '72 doesn't have climate control and there is always a fan that runs to circulate air.

[cean]

Ia have a 84 , the shop book says it is normal for the fan blower to stay on even when switch it off with the automatic climate control

[Abnorml]

Thanks. That's mainly what I wanted to know if it was suppose to blow all the time. I need to get my manual and try and fix the heat.

[Riff Raff]

What you are experencing is GM's Positive Ventilation system. Keeps the air fresh so you don't choke on fumes, gas fumes, both kinds.

[Morella]

There is one other thing, which can allow the fan to blow at higher speeds when the car is cold. On some Caddy engines, there is a switch on each cylinder head. The left one turns on an overheat light and switches on the key buzzer. The right one, usually under the alternator wiring, turns on the fan when the engine warms up. Although the heads are interchangeable, the switches have to be swapped around. Some people will bypass the fan switch by grounding the wire that goes to it, which will allow the fan to run at any speed, and blast you with cold air. People who have the switches swapped will find that the key buzzer and overheat light come on as soon as the engine warms up, so they unplug it, disabling the last-resort overheat warning.

Using a diagram is helpful, but it's easier if you know the background of the system. It is supposed to run at low speed all of the time, and the compressor (subject to thermal switch or pressure switch control) will continue to run all of the time once you turn it on. I find the latter to be annoying, and a waste of fuel, so I usually bypass that feature.

-denise