DenverDutch

I've got a '74 Omega, 350/350 with factory A/C.

When the ignition is on, the HVAC fan/blower is on; on low but always on. Don't like that. Is there any way to rewire it so the fan doesn't come on unless I turn the fan on with the switch?

Next problem. The fan/blower switch has 4 settings, low, medium, high and extra high. The extra high doesn't work in either heat or A/C setting. I've tried changing a few obvious parts but it still doesn't work. Is this a common problem? Any suggestions or troubleshooting directions?

One more related problem. Fresh air. In the VENT mode, the air that comes in is hot even when it is relatively cool outside. Vent air is only cool when it's really cold outside. The air coming in doesn't smell like it's coming from the engine compartment but it sure feels like it. Haven't been able to find a drawing or diagram of the ventilation system. Where does the 'fresh' air come from??

DenverDutch

p.s. Thanks Joe, for the info on disc brakes.

Allan R

Believe it or not that's how the car was designed - always have air circulation in the cabin. If you don't want the air circulation - turn the AC to OFF. That should also turn off the fan.

What have you changed out? I'm not sure if the 74 AC is like the stuff on 68-72. Did you change the water valve at the rear of the intake? Also check the vacuum line that runs to it - it controls the very high and cold settings.

I had that problem once with an AC car. Prolly one of your vacuum lines to mode doors is leaking vacuum. May be just brittle with age. Could also be a faulty vacuum pot. The guy who know AC is Rob Young (Rob71nLady72). Maybe check with him?

MDchanic

As Bill Gates says, "It's not a bug, it's a feature."

Sure. Just put a switch in the brown wire that supplies the fan switch.

I have gone through elaborate descriptions of this before, which you should be able to find by searching.
The HIGH setting sends power to the HIGH FAN relay in the engine compartment, which switches the supply from the dashboard switch through the resistor block to a supply from the horn relay terminal screw, through a 30A inline fuse, directly to the blower.
Steps to check:

1. Switch ignition ON (engine OFF)
2. Switch fan from #3 to #4 (HIGH) positions. Listen carefully for the tiny click of the relay inside the engine compartment. If you hear the click, you know that the circuit is good through the relay, which is to say the fan speed switch is good.
3. Follow the heavy wire from the HIGH FAN relay to the horn relay. Find the inline fuse. Check it and clean contacts. Recheck.
4. Check the continuity of the relay when in the HIGH position.

Your problem is somewhere in the above, including all wires and terminals.
Go find it.

That's normal.

From the cowl vent, right below the bottom edge of the windshield, just like on most modern cars.

- Eric