Art20c

Guys, any idea how hard is it to replace?

Calgary Ole

First as Bill would probably agree, make sure it is moving when you move temp from low to high( mine is mertric so 18 to 30 degrees ) Car on and best on an auto setting. Go ahead and gently pull or push the arm to get it moving if stuck.

really easy to remove with two screws and just pop arm off.

Art20c

When I was checking HVAC, I pulled center console apart, I had this setting motor uncovered and it looked to me as if it was part of the whole heater unit box, connected to it by rivets. P.S. Lever moves up no problem, just set higher temp, but when temp button moved to lower temp setting, motor does not respond

Calgary Ole

My car is a 90 so I may have you looking in the wrong place, I know that mine is located next to the steering column above your right knee as you would be sitting.

Art20c

Yeap, mine is in the same location.

Calgary Ole

I am a newbie but have spent many hours on my own HVAC, I may have missed a post from you but is the motor working or is it stuck.
Also, you have to be sure that your vacuum actuators are not leaking to be sure the head unit is okay( easy to bypass)

Art20c

Looks like I have faulty setting motor. Head is OK. Vacuum and sensors are OK. Did extensive testings. I would say I'm 100% sure problem is in setting motor, may be electric boards inside are faulty, given that under low cabin temperatures this motor works just fine. If it is easy to replace, I would do it.

Calgary Ole

If you find a way to repair it let me know as my atempts to clean and lube have failed.

Art20c

I will

Bill Ball

It appears to be pretty easy. Two screws accessible from below.

Used from 928Intl is OK with me - new are $600.

StratfordShark

I recently completed testing my setting motor which I suspected was faulty. I was suspicious that it always wantd to move to full hot position unless I had the temp slider at full cold where microswitch engaged.

In fact it was operating perfectly, just that in very cold winter we'd had the temp in garage was always too low so the system was correctly trying to reach warm cabin temp! Now weather has warmed up and car is on the road the system works beautifully. I had overhauled it recently with new cabin temp sensor (it had gone way out of spec and resistance was too high at all temps) and new internal sensor fan (old motor hardly turned).

The settings motor is easy to remove but in practice very uncomfortable to hang upside down in footwell (for RHD it's above driver's left kneee - just needs shelf removing that side for access)! Two bolts, then just use a screwdriver blade to pop plastic rivet out of motor arm. The rivet is on end of long metal rod which you leave attached to mixer flaps. Note the plastic rivet is only accessible when arm is driven to full cold.

With setting motor sitting on floor it was easy to test. There's an excellent series of tests in the workshop manual but you'll need a multimeter to probe the connectors.

I could confirm the control system worked ok by using wife's hair dryer to blow warm air at cabin temp sensor to simulate cabin warming up. Turned out system was very responsive.

One thing I noticed is that there's very little clearance (at least on RHD cars) for the long metal rod to mixer flaps to move up and down. There's a little leeway in exactly where the motor is bolted into brackets, so make sure it's positioned so thatthe arm can move freely to and from the full hot and full cold positions. Obviously you can only check this with motor re-installed. If it hangs up just loosen the bolts and move motor into a better position before tightening down.

You said you'd checked sensors, but can you confirm that you are moving between the correct (1000 ohm) range of resistance at end of sensor string when you run from full cold to hot at the temp slider, and that the actual resistance values are in spec (my faulty cabin sensor was forcing the whole resistance string value too high, so system always thought the cabin was cold)?

Art20c

Your problem is, I believe, called "all or nothing" which is a symptom of faulty outside air temp sensor. Mine is little different, even when temp selector button is set to its very left (lowest temp) position, setting motor stays at whatever position it was before temp was set to low. In other words, motor will go up but not down. The only way down is with the 6mm wrench snapped on the nut of that metal lever and pulled manually.

Bill Ball

Well, Matt (Edco) and I took care of this today on his car. We replaced the setting motor. The hard part is wiggling into position under the driver side dash. The package tray needs to come out and then the unit is quite visible. Matt's motor would not move. We unplugged it and before swapping units just plugged the replacement in and observed the motor and lever arm moved with change in the position of the temp slider, and the heater valve now closed and opened as it should. I took the bad unit apart. The motor is not seized is about all I can say. Matt is happy with the replacement and his now controllable heater valve. so although the most common cause of heat all the time is a faulty heater valve or loss of vacuum to it, setting motor unit failure can cause the valve to fail open when the system is switched on. I'll find out next week whether it can cause to valve to fail closed as well when I get to look at another car that has no heat.

edco

Bill,

Thanks again its working like normal....

vsalvato

Hi guys... gretings from hot northern Italy... and as warm weather comes up guess what, the A/C on my S4, MY88 does not work, hence I decided to dig into the precious Rennlist forum. When i start A/C I hear that it tries to work but I get nothing out of the blower but hot air. Occasionally, and for a short while i get A/C but after a couple of min max (typically when I start the car after a long rest in the garage), but after that it turns back into hot-air and what is funny is that it does not seem to matter where I set the temp control sliding cursor... no change. I have been wrognly directed by my auto-electrician to the A/C control unit but I suspect that it might be the fautly exterior temp sensor... if so (and an expert opinion would be appreciated although the kind of info that I offer, I understand, is limited). If the sensor is to replace, would it be hard to do? How expensive is the part? would it be good to replace all the sensors at once (I guess there is an external, an internal and a third temp sensormanaging the A/C control unit?