Rear Heat/AC Unit stuck on Heat - 98 3.8L

98 3.8L 112k....Rear Heat/AC unit only blows hot air. Front AC blows real cold. I think they work off the same compressor. Behaves the same with front switch set to Heat or AC or Rear Control. I can't find a dedicated fuse or relay for only the rear unit. Fuse 21 controls the switch and it is good.

1. Could a relay not be working? Not switching the air flow from the lower path heat to the upper path AC?

2. The cylinder arm switch defective - not moving the air deflector from sending air over the heater core to sending air over the evaporator coils? This cylinder arm switch DOES NOT move when switching from heat to AC.

Tomorrow, I'll remove the cylinder arm switch and try to physically move the air damper to send air the AC way. Heck, if this works...I'll just leave it and worry about it when it gets cold.

Anybody have this problem?

Hi
Most likely lack of vacuum at the rear actuator/blend door. If you take the sidewall trim off below the rear a/c controls you will find the blend door and its actuator. I think the vacuum line is green. Check line for vacuum at around 13"/hg . If the vacuum is good, the actuator (vacuum motor) is kaput. If no vacuum trace green hose for a leak. If your front controls - defrost, mix, floor, dash work o.k. you have good vacuum at least to the vacuum block under the dash, so problem is between there and/or at the rear actuator.

Thanks, busboy4...real good data...the haynes is woefully inadequate here.

I have normal venting, defrost, floor, mix up front. I pulled the vac line off the cylinder arm switch ( bottom left of photo) and physically moved deflector to shoot air out the AC vents...still real hot. I feel no vacuum out of this white vac line (don't have a gauge).

So as you say the problem is upstream of this. Can you point out the actuator/vacuum motor from this photo? I had to leave town for trip before I could get any deeper pulling the trim panels off.

http://home.comcast.net/~dougand3/Auto/rearAC_heat.jpg

Hi
The actuator(vacuum motor) I'm talking about is what you moved. It is the mechanism below letter A in the photo. It operates the arm you moved to position a door inside the triangularly shaped area the right of the actuator arm. With no vacuum (heat) the door is against the upper side of the triangle and all air goes through the rear heater core and down. With vacuum the actuator arm is pulled into the actuator(down), the door is pulled against the bottom of the triangle and all air goes through the rear A/C evaporator coil and up to the roof vents (air moving right to left in the photo from the fan which is the round housing).

If you moved the arm and were able to only get hot air out of the top I am not exactly sure what is up. Now, my knowledge and manual are for a '96, but I think it is no different as your diagram exactly matches mine in the factory manual (I was wrong of course about the color of the vacuum line: it of course is white, which is what my manual shows). I wonder if you are actually making cold air with your rear evaporator? You can check outside under the left side directly below where the fan and blend door are located. Running under the belly of the van you will see four 1/2 to 1" diameter aluminum lines running under the van and then up into the rear A/C/heat area. With the van running and A/ C selected on, you should have hot and cold line(s) - 3 hot for heater core water(1) and return(2), and the A/C line from the condenser to the rear evaporator(3) and then one cold which is the A/C suction line(4). If the 98 is like the 96 the two aft lines are the A/C lines and the cold one should be forward of the hot one.
Point being, if you cannot find a cold line with the A/C running for a while, the rear evaporator is not making any cold due to a clog in the refrigerant line or something of that sort.
Back in the van, just to check you can run the A/c and heat and watch to see if the actuator moves as you change from commanding heat to A/C with the front control. You should see it move as you change out of A/c settings over to the heat/defrost side.

I don't know that your problem is inside unless there has been a serious dis-connect between the actuator and the blend door inside i.e. is the blend door even moving? Has it broken off? Does not seem likely as you were able to force air out of the top but it is worth verifying exactly what you think is happening back there.
Let us know what you learn.

Thanks, busboy4.
So what I'm calling the cylinder arm switch is the actuator/vacuum motor...I shouldn't make up terms - LOL.

I depressed the arm to change deflection for only 10 secs...I expected some change - move from hot to very warm. I should have done it much longer. I will re-check Tues nite.

Let's suppose after a minute of changing blend door to all AC, it gets cold. Would I have problems if I remove the actuator vacuum motor and tape the blend door to all AC flow?

Thanks, busboy4.

Let's suppose after a minute of changing blend door to all AC, it gets cold. Would I have problems if I remove the actuator vacuum motor and tape the blend door to all AC flow?


I don't see why it would be a problem. You could just run a summer/winter setup. I would encourage you to figure out if it is the actuator, or low/no vacuum just so you know. If you are going to leave the white vacuum line loose seal the end of it with duct tape or similar to preclude a vacuum leak.

I'm back in town.
Problem is solved....the expensive way. Girlfriend (her van - I just maintenance it) needed the Windstar for a 2000 mile/10 day trip with 3 teenage girls who would W-H-I-N-E if they got hot. She wasn't confident I'd figure it out before thurs am (neither was I). So today, she took the van to the Ford Stealer...$300 for a new switch, R134a and a cleanup job.

Front panel switch for Rear AC/heat unit - F68Z-19986-AA. $31. Blue/AC on L Rotation and Red/Heat on Right. It is electrical AND vacuum. I never would have thought that.

When I plugged that switch part number into google, it showed this thread. Good reading.

http://www.cartrackers.com/Forums/live/fordwindstar/1230.html

Glad it's fixed for the girls but feel cheated that I couldn't try the Summer/Winter setup after removing the actuator and securing the Blend Door as all COLD or all HOT.

But it's good we went to the dealer and spent beaucoup $ because the girls will be cool, Windstar is in factory AC specs, got a free carpet vacuuming, I didn't have to touch that R134a can and get chilly fingers. (Help me out here, I'm running out of BS to deaden the pain)

If girlfriend is happy, much pain will be deadened. :naughty:

This is a fantastic web site! Solved my problem with no AC, just heat from the rear AC in my 96 Windstar. I jumped the 2 vacuum connections in the plug I took off the back of the rear AC control switch in the dash. I used a piece of stipped electric wire insulation as suggested which fit over the vacuum connections, and the rear vent swithed to AC. I then knew the switch was the problem. Got the switch for $26 at Ford, and put it in myself. One helpful tip on getting the dash pannel of: Pull out the cup hlder and it exposes the 2 screw bolts that need to be removed. Then pull the pannel out carefully. It just spring clips on. Then you can get at the controls. Thanks to all the posters here! Tom C.