AC/Heater keeps blowing cold/hot air when ac is turned off and car is running

[A4LD_Nghtme]

I can't figure out why, but my ac/heater blows air when it's fully in the off position. It does not do this when the car is off but when I'm driving and get too warm I turn off the heater like anyone else but the darn thing keeps blowing even though it's slight. But it's slight enough to keep overheating the cabin. So I have to set it to in between cold and hot to not get too hot yet it is still blowing air although bearable temp. Any ideas?

 

[ekrampitzjr]

I can't figure out why, but my ac/heater blows air when it's fully in the off position. It does not do this when the car is off but when I'm driving and get too warm I turn off the heater like anyone else but the darn thing keeps blowing even though it's slight. But it's slight enough to keep overheating the cabin. So I have to set it to in between cold and hot to not get too hot yet it is still blowing air although bearable temp. Any ideas?

Most likely to me: a bad selector switch that has a short in the off position.

 

[James Morse]

New Motorcraft switch $70.
If it's not too hard I'd pull switch and test per above for short.
I don't know what they look like but I assume they have a setting labeled 'OFF' which is different than turning it all the way to the left which one might intuitively think is off, but I'm assuming you are completely familiar with your truck (and I'm not) so like ekrampitzjr said sounds like short.
It might not help, but, could be worth it to get switch out and spray some CRC electronic cleaner in there and work it back and forth. A shot in the dark, just in case you could save the switch.
It doesn't look like you have full "off" for the fan, only for the vents. If I'm looking at the right one. So fan would always be blowing. Seems a bit odd; others will know more.

 

[RonD]

If we are talking about a 1990 BII/Ranger then there is an OFF for fan/blower control
Up to 1994
These used slider bars for vent and temp controls

In 1995 Ford switch to Knobs for climate control, and there is no OFF on fan control, just low
If you want fan to be off you must select OFF on Vent control, then fan will turn off


So assuming 1994 or earlier then yes the fan speed control is the issue or the Resistor Block in engine bay
All years use the Ground to control fan speed
Fan gets 12v directly with key on
The Fan speed control does fans ground wire
OFF would, of course, be No Ground at the fan speed control switch
If fan was still on then that "disconnect" is shorting to a ground somewhere

Resistor Block is what the Fan Speed controller is connected to, so if any of its wires were shorted to ground then no OFF

Its a pretty straight forward wiring system

 

[James Morse]

sorry, thought he was talking about the Bronco. Per usual Ron nailed it.
Therefore there is no setting where fan is totally off, and, you're getting air. You can't be on the highway and turn the fan off and have air coming through the vents.
When I think about it, it's a little weird, but I guess I just accept that the fan will run all the time, if you want air.

 

[RonD]

1995 and up, fan will shut off if you select OFF on the Vent control, this turns off the Blower Relay, cutting 12volts to fan motor

 

[James Morse]

Yes I don't know why I was mixed up because both my trucks are identical in that way.
A lot of times when I park at home I turn it to OFF then I don't have it running right away when I turn the key to ON.
I can't remember if it runs with key in START but if it did, that'd be another reason to turn it OFF.

 

[SenorNoob]

In mine when the fan is off, the outside air is selected, and moving highway speed (55MPH), I have as much air flow as medium fan speed. Have to turn that outside air off to stop it.

 

[James Morse]

Cool. I don't mine if mine does that, but now I'm going to check because I'm curious.