Mark VI ATC Sensor

[mercurygm88]

So after finding out last night that my 83 Mark VI has no heat, I'm looking for a solution. it appears the most likely issue is the ATC sensor which is pretty much unobtainium as I understand it. This isn't a huge deal as this car will be garaged in the winter but there may be some cool fall or spring days/nights when I want to drive it. So what I'm wondering is

1. is there any chance at all of finding a NOS or working ATC sensor and if so how hard is it to get too? Do I need to remove the dash pad or just the trim on the front of the dash?

2. If it's unlikely that I'll find one is there a way of bypassing the ATC sensor? Could I potentially splice into the vacuum line under the dash and put an air tight valve in there to switch from hot to cold? Or could I run the line up into the glove box and put a hose barb in it so that unplugging it and capping the line would move the door one way and reconnecting it would move it the other? I'm thinking the glove box because it's easier to get too than dropping the glove box every time I want to connect or disconnect the line. The valve idea would be ideal if it's even possible I could just mount it under the dash within reach.

Thanks in advance for any ideas or solutions.

[sly]

If the blower doesn't blow, bypass the thermal blower lockout (inline on the heater hose to the heater core). It won't turn on until temps in the hose are up... if it's working. 10 gauge wire. Can just cut and solder together.

If it's the cabin temp sensor... just unplug the vacuum line to the blend door behind the glove box and plug the line. You will have full heat. Obviously no control over temp, but can modulate fan speed manually.

These steps can get you by until parts can be found/fixed.

[Mainemantom]

If you are looking for the blue ac temp sensor under the top of the dash pad, I believe the part number is : Motorcraft YH-409 or E3VY-19C734A
Hard to find but not impossible

[mercurygm88]

If the blower doesn't blow, bypass the thermal blower lockout (inline on the heater hose to the heater core). It won't turn on until temps in the hose are up... if it's working. 10 gauge wire. Can just cut and solder together.

If it's the cabin temp sensor... just unplug the vacuum line to the blend door behind the glove box and plug the line. You will have full heat. Obviously no control over temp, but can modulate fan speed manually.

These steps can get you by until parts can be found/fixed.

I’m pretty sure it’s the temp sensor, the fan works fine, AC works fine but is of course stuck on full cold.

I’m thinking about splicing into that blend door line and lengthening it so I can reach it from inside the glove box. That’s really no big deal especially if I only have to do it twice a year.

[mercurygm88]

Thanks Tom. I’ll look into that and see what I can find.

[Lutrova]

Check out this thread for some ideas on repairing your ATC sensor. I believe that so long as the needle valve/plunger in your sensor is still there, these sensors should be repairable. I've only managed to fix one so far though, so I'd be interested to see if you could replicate the results.

In the mean time, you can bypass the sensor without having to splice into any lines. The supply and return lines to the ATC sensor unplug from the rest of the system, and you can get to it from behind the glove box. Once unplugged, just run some new line between the two lines on the system side of the connection, bridging the vacuum supply and servo lines. That will give you full cold without the potential vacuum loss and subsequent full heat/defrost behavior that a bad ATC sensor can create.

[mercurygm88]

Check out this thread for some ideas on repairing your ATC sensor. I believe that so long as the needle valve/plunger in your sensor is still there, these sensors should be repairable. I've only managed to fix one so far though, so I'd be interested to see if you could replicate the results.

In the mean time, you can bypass the sensor without having to splice into any lines. The supply and return lines to the ATC sensor unplug from the rest of the system, and you can get to it from behind the glove box. Once unplugged, just run some new line between the two lines on the system side of the connection, bridging the vacuum supply and servo lines. That will give you full cold without the potential vacuum loss and subsequent full heat/defrost behavior that a bad ATC sensor can create.

Thanks for the info. If I bridge those particular lines I'll be on cold air only unless I put the back correct? I'm currently on cold air only and at this point I'm just dropping the glove box and unplugging the line on cool nights that I drive the car to get heat. I've only done it once so far but it doesn't seem to create a significant vacuum leak. I don't have the issue with my heat defaulting to defrost like happens when the check valve behind the intake fails. I'd like to come up with a way to switch between hot and cold without dropping the glove box every time. I keep a lot of stuff in there and it's kind of annoying. So if I could run a piece of line into the glove box, with a hose barb in it or a 3 way ball valve with an L shaped passage I think that would work.

[Lutrova]

Yes, simply bridging the lines does nothing more than give you steady, full cold. If you wanted to do something fancier you certainly could, and the things you're considering sound like you're on the right track. I only suggested disconnecting the sensor lines and bridging the junction as a starting point that would save the rest of your system's vacuum lines from mutilation.

[mercurygm88]

I don’t intend to mutilate anything. If I add in a valve I’ll add it at the end of the line that currently goes to the actuator solenoid. That way it can be removed without damaging any of the original components.