It's HOT in here
11-02-2003, 07:15 PM
#1
Racer
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It's HOT in here
Help My heater runs full hot any time its on. 87 S4.
All vacuum actuators check out as do all vacuum lines.
HVAC control head pot for temp setting reads according to manual.
Full hot and full cold micro switches check out OK.
Blower runs correctly.
Heater valve works correctly.
With the HVAC system OFF both sliders left, everything Ok heater valve closed.
With upper temp slider still full cold, as soon as I move the bottom control on, heater valve opens and it's hot in here.
So, am I looking at cabin temp sensor or what?
Trying to enjoy fall temps. Thanks
All vacuum actuators check out as do all vacuum lines.
HVAC control head pot for temp setting reads according to manual.
Full hot and full cold micro switches check out OK.
Blower runs correctly.
Heater valve works correctly.
With the HVAC system OFF both sliders left, everything Ok heater valve closed.
With upper temp slider still full cold, as soon as I move the bottom control on, heater valve opens and it's hot in here.
So, am I looking at cabin temp sensor or what?
Trying to enjoy fall temps. Thanks
11-02-2003, 08:46 PM
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Racer
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Still confused. I know where the sensor is but my feeble mind thought that a failure of that sensor would couse the system to ONLY operate on full cold or full hot. Mine runs full hot even when on full cold. Iused to be able to bring in nice fresh outside unconditioned air. Not now.
Am I wrong? I am far too often these days.
Am I wrong? I am far too often these days.
No heat!
11-02-2003, 09:07 PM
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Racer
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Well if it isn't the Ralph Cramden of the 928 world. Hey Tony. Whenthis started and I started checking stuff out, I noticed that the heater valve is open any time the bottom slider is moved from off. Does that sound right?
Jay K. is about the only one who could get away without coolant from now till about May.
Jay K. is about the only one who could get away without coolant from now till about May.
11-03-2003, 10:36 AM
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Checked the outside temp sensor this am reads 397 ohms @ approx. 72 deg F. So that seems to be outside specs. Anyone have specs for inside temp sensor? Can't find them in the WSM.
11-03-2003, 12:10 PM
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Still searching! The setting motor will operate when moving the temp selector from full cold toward full hot, however when I move the temp selector toward full cold the setting motor DOES NOT move back toward full cold. Based on the date on the setting motor it is not the original. 1992
Connections look good and clean.
Connections look good and clean.
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11-04-2003, 09:51 AM
#8
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Ok Guys here's where I stand as I've tested and retested. Setting motor was replaced in 1992. Setting motor will not return to full cold position but will cycle toward heat. Outside temp sensor reads 397 ohms @ approx. 72 deg F. Inside temp sensor reads 1258 @ 65 deg F. Output of top temp slider reads range of 677-965 ohms (manual states approx. 750-1750 with a 1000 ohm swing) Not in a position to throw money at this one. Would the bad pot in the control head cause my symptom. Any help would be appreciated. Thanks
11-04-2003, 02:44 PM
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I'm wondering if there's some difference between the '87 climate control and the '92 climate control. You might want to see how many control units there are, and if there was a change by '92.
That said, it does seem like the control unit is getting some bogus signal from one of the temp senders. If you make the outside temp sender tell the controller that it's hot outside (unplug or bridge the pins on the sender - dunno if 0 ohms or infinite ohms means warm) and likewise have the cabin sender send "hot" as well, what happens? Perhaps some combination of disconnecting/shorting the cabin and outside air temp senders will indicate where the problem is?
Bryan
That said, it does seem like the control unit is getting some bogus signal from one of the temp senders. If you make the outside temp sender tell the controller that it's hot outside (unplug or bridge the pins on the sender - dunno if 0 ohms or infinite ohms means warm) and likewise have the cabin sender send "hot" as well, what happens? Perhaps some combination of disconnecting/shorting the cabin and outside air temp senders will indicate where the problem is?
Bryan
11-04-2003, 09:57 PM
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>Outside temp sensor reads 397 ohms @ approx. 72 deg F.
Spec is 588 Ohms @ 20 Deg C (68 Deg F), 457 Ohms @ 30 Deg C.
>Inside temp sensor reads 1258 @ 65 deg F.
Spec is approx 2570 Ohms @ 20 Deg C.
>Output of top temp slider reads range of 677-965 ohms (manual states approx. 750-1750 with a 1000 ohm swing)
Spec is approx 760 Ohms to 1760 Ohms. "It is important, that the resistance value changes by approx. 1000 Ohms each time."
If you check the resistance of the total string at the setting motor, you should have 3918 Ohms with the lever on cold, 4918 with the lever on hot (at 20 Deg C ambient).
Sounds as if you would have approx 2280 (cold) to 2560 (hot). I doubt that would work.
It might be worth trying to take the control unit apart and cleaning and checking it. I seem to remember that someone posted here that they had done that - perhaps a careful search of the archives is in order...
Spec is 588 Ohms @ 20 Deg C (68 Deg F), 457 Ohms @ 30 Deg C.
>Inside temp sensor reads 1258 @ 65 deg F.
Spec is approx 2570 Ohms @ 20 Deg C.
>Output of top temp slider reads range of 677-965 ohms (manual states approx. 750-1750 with a 1000 ohm swing)
Spec is approx 760 Ohms to 1760 Ohms. "It is important, that the resistance value changes by approx. 1000 Ohms each time."
If you check the resistance of the total string at the setting motor, you should have 3918 Ohms with the lever on cold, 4918 with the lever on hot (at 20 Deg C ambient).
Sounds as if you would have approx 2280 (cold) to 2560 (hot). I doubt that would work.
It might be worth trying to take the control unit apart and cleaning and checking it. I seem to remember that someone posted here that they had done that - perhaps a careful search of the archives is in order...
11-05-2003, 10:33 AM
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Thanks for the input.
Wally, I had already cleaned the outside temp sensor connections, opened the controller and cleaned the gunk out, used an eraser etc to clean the plug connectors and the switch sweeps etc. Checked the two micro switches at max hot and max cool. My feeble mind still cannot determine what condition reverses the voltage to the setting motor to cause it to move toward the full cold position.
Kevin B. has been kind enough to offer a NIB controller to swap with mine to see if that is a fix. I will be doing that maybe today or tomorrow. Will post the results.
Wally, I had already cleaned the outside temp sensor connections, opened the controller and cleaned the gunk out, used an eraser etc to clean the plug connectors and the switch sweeps etc. Checked the two micro switches at max hot and max cool. My feeble mind still cannot determine what condition reverses the voltage to the setting motor to cause it to move toward the full cold position.
Kevin B. has been kind enough to offer a NIB controller to swap with mine to see if that is a fix. I will be doing that maybe today or tomorrow. Will post the results.
11-05-2003, 11:35 AM
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Burning Brakes
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Ed and Wally et al.,
This thread is a good eduction to supplement my reading of Wally's excellent 928 HVAC primer. I haven't had the time to delve into my Shark's issue (cool but not cold air in front / ice cold air from rear unit). Wally was kind enough to offer his thoughts last time and another member here who recently tackled some vacuum issues in his car offered to walk me through the procedure of testing the system with a Mity Vac. I'll be buying one of those soon...if anyone has a used Mity Vac for sale or can suggest a vendor...please PM me. Again, as a new member, I love to read threads like this one. Carry on fellas...sorry to intrude.
Best,
Tim
This thread is a good eduction to supplement my reading of Wally's excellent 928 HVAC primer. I haven't had the time to delve into my Shark's issue (cool but not cold air in front / ice cold air from rear unit). Wally was kind enough to offer his thoughts last time and another member here who recently tackled some vacuum issues in his car offered to walk me through the procedure of testing the system with a Mity Vac. I'll be buying one of those soon...if anyone has a used Mity Vac for sale or can suggest a vendor...please PM me. Again, as a new member, I love to read threads like this one. Carry on fellas...sorry to intrude.
Best,
Tim
11-05-2003, 12:02 PM
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Tim, Check out John Pirtle's write up on adjusting the mixer flaps. If they are off it could cause your symptoms. HTH
http://members.rennlist.com/pirtle/svc_ac.html#mix
Just click on the link.
http://members.rennlist.com/pirtle/svc_ac.html#mix
Just click on the link.
11-05-2003, 12:07 PM
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Hello Ed,
I will check it out right now...thanks for the advice...and referral. WallyP seemed to think that would be a good place to start too if the vacuum actuators check out (i.e., no leaks). Good luck with your HVAC project...
Best,
Tim
I will check it out right now...thanks for the advice...and referral. WallyP seemed to think that would be a good place to start too if the vacuum actuators check out (i.e., no leaks). Good luck with your HVAC project...
Best,
Tim
11-06-2003, 12:04 PM
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Ed,
I believe the HVAC is one of the many systems in the 928 that has too many sensors and too many control elements just to control one variable, cabin temp.
There are three resistance sources (outside sensor, inside sensor, and the control pot in the HVAC head) in the HVAC loop. Based on the information you gave, it appears that ALL 3 are not functioning properly. This is difficult to believe. Also, your total resistance should keep the setting motor at the cold end, not the hot end, which would leave me to believe the setting motor is suspect too.
You have a couple of choices. (1) You can replace all the sensing elements (probably one by one to see where the problem is) and setting motor. Thsi is an expensive option. Or (2) you can figure out what you need in terms of HVAC depending on where the car is kept (do you need heat, etc). My car, originally a florida car, had the heater core inlet hose plugged when I bought it. Since I live in Wisconsin, I need heat (especially for the wife) but not too frequently. I was having some but not all of your problems. If you're interested in what I did send me a PM, it may give you some ideas. It cost me very little $ and some time.
I believe the HVAC is one of the many systems in the 928 that has too many sensors and too many control elements just to control one variable, cabin temp.
There are three resistance sources (outside sensor, inside sensor, and the control pot in the HVAC head) in the HVAC loop. Based on the information you gave, it appears that ALL 3 are not functioning properly. This is difficult to believe. Also, your total resistance should keep the setting motor at the cold end, not the hot end, which would leave me to believe the setting motor is suspect too.
You have a couple of choices. (1) You can replace all the sensing elements (probably one by one to see where the problem is) and setting motor. Thsi is an expensive option. Or (2) you can figure out what you need in terms of HVAC depending on where the car is kept (do you need heat, etc). My car, originally a florida car, had the heater core inlet hose plugged when I bought it. Since I live in Wisconsin, I need heat (especially for the wife) but not too frequently. I was having some but not all of your problems. If you're interested in what I did send me a PM, it may give you some ideas. It cost me very little $ and some time.