325 Heater won't shut off

Skips951 · 10-10-2002, 06:02 AM

Hi guys,

I have a '93 325is with the dual zone climate control head unit, and the heater wont shut off. The heat stays on full hot no matter what position the 2 dial thermostats are in. The fan still works fine, and if I use the vent control Hot/Cold I can get the air to work or at least cool air from outside which is ok now that its not too cold out, but since it is an on or off control the car is always too hot or too cold. I haven't pulled the head unit out yet, but any feedback would be appreciated.

Thanks

Wayne 962 · Wayne 962's Garage

I've got a strange problem with my heater unit too. The A/C doesn't work until the car has completely warmed up. This could be a broken switch, or a broken temp sender (I believe that your car had two senders). Basically if the switch is broken - it's obvious it would be on all the time. If the sensor is broken, it may be telling the heat to go on all the time.

Does the fan turn on and off, or is the fan on all the time? After reading your post, I'm a bit confused...

-Wayne

swinston · 12-31-2002, 02:01 PM

I have the same problem with a 1994 318i. Lots of heat and I do the same as you to moderate the temp. The entire HVAC system works fine except for control of heater.

I did go one step as I was convinced the heater control valves were seized, not uncommon I understand, and checked the voltage at the connector for the valves. It appears there is power there all of the time regarless of where the temp contols are set. This makes me think there is a problem in the control unit or relay.

I won;t go much farther as it is January in Canada and the last thing I need is no heat. I will play with this and post what I find.

R.

Wayne 962 · Wayne 962's Garage

Is there a way to check the valves to the heater core? Or is that hidden under all that junk. Heater stuff is really the worst kind of problem, because you can never get to it easily...

-Wayne

swinston · 01-01-2003, 08:24 AM

The valves are fairly accesable but like everything a bit of a pain to actually work around. I plan to go further by unplugging the connector to the valves and using a small 12 volt battery, reversing the power leads, should get them to accuate. They are solenoids so logic tells me I should be able to open and close them in this manner.

I don't have a schematic of this function so am working on hunches.

R.

Wayne 962 · Wayne 962's Garage

Hmm, while I have't taken these valves apart, I have taken others apart in the past. I'm not sure about your logic of reversing the current - this typically doesn't work this way on cars. Valves like these are typically spring-loaded, and will open or close when the power is removed. Then again, I'm not sure about this one...

-Wayne

swinston · 01-01-2003, 04:25 PM

THanks I am working on guesses here.

Does the Bentleys manual go into any depth on this system?? The Haynes manual I have has nothing about the dual control system and next to nothing on the single.

At this point I need the heat more than not so unless I can get into one of my freinds service bays in his garage it will wait till spring. I can live with the fried right foot. Thank god for cruise control.

R.

Wayne 962 · Wayne 962's Garage

I don't have my Bentley manual in front of me, but it is much, much better than the Haynes manual, and appropriately priced as well. I would definitely pick up a copy...

-Wayne

Jared at Pelican Parts · 01-02-2003, 12:12 PM

I would think this would be a faulty cable or spring used to actuate one of the valves. What happens when you turn the heater on full blast? Do you see any condensation or water buildup? Also, have you checked your thermostat lately?

swinston · 01-04-2003, 05:31 PM

It appears the zone controls on the dash have their own water control valve mounted together as a unit on the firewall. There are 3 hoses leading into it controlled by a 3 pin connector 2-12 volt supplies and one common ground.I am sure my thermostat is fine and as I said in a previous posting the entire HVAC system works fine, no condensation etc., it just the heat you cannot control.

Wayne 962 · Wayne 962's Garage

When you flush the radiator, the manuals says to turn the two knobs all the way to hot, but doesn't say anything about turning the ignition on. This would make me think that this is not an electrical system, but is purely mechanical in some manner? I haven't dived behind the dash yet, so I have no idea...

-Wayne

swinston · 01-05-2003, 07:27 AM

very interesting. Thanks. I have ordered a manual so maybe I will become more educated. oh! oh! Is this sort of like reading the instructions?????

Scary have a good one.

R.

Wayne 962 · Wayne 962's Garage

I'm not sure now - as Bob540 on another post, mentioned that the swtiches are indeed electrical, which would mean that the Bentley manual contradicts itself?

-Wayne