W210 - 1999 (T) - Continued Heater Temperature Control Problems....

[rjsdavis]

Hi there all

I've had continued heater problem with my W210 - I've replaced most things that I can think of, and can't see where to go with it next....

In short, my car "used" to have problems with the fan speed, insofar that the fan would not be properly controlled by the settings on the left-hand dial. A hefty slap on the dashboard sorted this out - but I also had problems with the actual temperature of the air coming out of the vents as well, insofar that this was ALWAYS hot no matter what setting the the temp control guages were on. Also - the fan used to come on all by itself after about 45-50 mins of motorway driving.

Anyway - the fan controls have been cured because I have now installed a new heater control panel in the dashboard - there are no problems with the fan speed or it coming on by itself.

HOWEVER - I do still have the temperature problems - and this hasn't changed at all. One fixed - HOT - temperature that comes out of the vents no matter what setting they are on.

Before you suggest it, I have also replaced the duovalve as well - and this has made no difference at all.

I now don't know where to go with it - I've changed what I thought were the obvious items - and have run out of ideas!

I should also add, that my car used to have very significant electrical problems which turned out to the voltage regulator on the alternator. This was replaced, and these have all gone - it was things like windows that would stop working, cruise control that would sporadically stop working, regularly blowing bulbs etc etc - these have ALL gone - but I am wondering if a component of the heating system could have been damaged (apart from the main control panel and duovalve), that I haven't thought of.... Any ideas out there??? Any assistance would be very much appreciated.

 

[type49]

You could have a problem with either outside or inside temp sensors. Poss fault with aspheric motor next to front interior light. There is a small vent there which sucks in air & measures temp. Cut a piece of paper 1 inch square, Start engine & hold paper to vent, does it stick & then fall off when engine turned off?

 

[rjsdavis]

You could have a problem with either outside or inside temp sensors. Poss fault with aspheric motor next to front interior light. There is a small vent there which sucks in air & measures temp. Cut a piece of paper 1 inch square, Start engine & hold paper to vent, does it stick & then fall off when engine turned off?

Blimey - I didn't know that! I shall give it a try tomorrow - thanks!

 

[Parrot of Doom]

The duovalve looks to be a very simple piece of equipment. If you're getting hot air instead of cold, then its obviously not being controlled correctly.

I'd get a multimeter across the 3 terminals on the duovalve wiring connector (duovalve disconnected), and get a friend to adjust the temperature in the cabin - see what voltage changes are evident.

I doubt the heater panel is wired directly to the duovalve, so I would try and trace the connection and test for continuity - my guess (and its a guess) would be that something is wrong with the connection between the two devices (presuming that is, that the heater control panel is working correctly)/
.

 

[stevie d]

heater control problems

My 95 CE320 has had problems like this since I bought it. Heater full hot in any position except cold. Interesting to read comments. Whats the first thing to try guys?

 

[rjsdavis]

You could have a problem with either outside or inside temp sensors. Poss fault with aspheric motor next to front interior light. There is a small vent there which sucks in air & measures temp. Cut a piece of paper 1 inch square, Start engine & hold paper to vent, does it stick & then fall off when engine turned off?

Have done as suggested - and I'm pleased to say that the paper stuck fairly firmly whilst running - persumably indicating that this device at least seems to be working.....

I shall parrot of doom's suggestion tomorrow, and report back the findings.

 

[television]

Yes a volt meter on the duo valve when going from hot to cold would say quite alot

 

[rjsdavis]

The duovalve looks to be a very simple piece of equipment. If you're getting hot air instead of cold, then its obviously not being controlled correctly.

I'd get a multimeter across the 3 terminals on the duovalve wiring connector (duovalve disconnected), and get a friend to adjust the temperature in the cabin - see what voltage changes are evident.

I doubt the heater panel is wired directly to the duovalve, so I would try and trace the connection and test for continuity - my guess (and its a guess) would be that something is wrong with the connection between the two devices (presuming that is, that the heater control panel is working correctly)/
.

I was just sitting here thinking about your suggestion, and I will try it tomorrow, BUT here's my poser....

In the cabin - it is dual zone air-con / climate control - therefore if I had the passenger side on max cold, and the driver side on max hot - how does the duovalve know how to interpret this with only one power cable?

Surely, if one side of the car is asking for hot, then it needs to blow hot - but what then happens to the other side that is demanding cold?? I just don't see how the duovalve interprets or indeed manages to provide both simultaneously??

I shall try the multi-meter anyway, but I do recall a Merc engineer telling me (yes - would you believe that I have spoken to one!! - Jason at Medway Mercedes), that apparently the heater controller "pulses" a current to the duovalve. If I recall correctly - the default setting (in case of failure) is HOT so that a driver is not stranded and can still clear the screen and drive in cold conditions - and that the "pulsing" if it is all working correctly, is what shuts off the hot air and provides cold - I can't remember more than that... Does that make sense?

This being the case - if it pulses (if it is working), would I not get jumpy voltmeter readings?

 

[rjsdavis]

The duovalve looks to be a very simple piece of equipment. If you're getting hot air instead of cold, then its obviously not being controlled correctly.

I'd get a multimeter across the 3 terminals on the duovalve wiring connector (duovalve disconnected), and get a friend to adjust the temperature in the cabin - see what voltage changes are evident.

I doubt the heater panel is wired directly to the duovalve, so I would try and trace the connection and test for continuity - my guess (and its a guess) would be that something is wrong with the connection between the two devices (presuming that is, that the heater control panel is working correctly)/
.

I forgot to say "Thanks" for another useful suggestion from yourself.

I told you this car was a lemon!

 

[television]

Yes with a stepping motor it is pulses thinking about it so a meter would not be much good,i doubt that you have a scope.

Is it a 210026,or 226

 

[Parrot of Doom]

In the cabin - it is dual zone air-con / climate control - therefore if I had the passenger side on max cold, and the driver side on max hot - how does the duovalve know how to interpret this with only one power cable?

The duovalve has 2 valves/cylinders, 1 for each side of the car. The cable to the valve IIRC has 3 pins. One of those pins will be common, perhaps the middle pin (perhaps zero volts, but thats a guess), each of the other 2 pins will control an individual valve.

If neither side of the car is controllable, that suggests to me that at the very least, the common connection on that connector isn't doing anything, because it either isn't connected to the heater control panel for some reason (and likely neither will the other 2 pins be connected), or because the panel is faulty.

Someone will be along shortly to tell you which position the duovalve defaults to when not connected, I have a feeling that it's the fully open (hot) position, it would make sense in an emergency to have it fail on hot.

If someone knows if there is supposed to be a direct connection between the heater panel and the duovalve, then it would be a very simple matter to isolate the pins on the back of the panel, and run some wiring through the window and into the bonnet, to test if things are working properly - but somebody needs to confirm that before you attempt it.

 

[rjsdavis]

Yes with a stepping motor it is pulses thinking about it so a meter would not be much good,i doubt that you have a scope.

Is it a 210026,or 226

I assume you are talking about the chassis number? Ifso, it is WDB2100252A855755? There isn't a 026 or 226 in the number?

 

[television]

I assume you are talking about the chassis number? Ifso, it is WDB2100252A855755? There isn't a 026 or 226 in the number?

No, the 210025 is fine, see if i can find a known problem, later in the day

 

[rjsdavis]

No, the 210025 is fine, see if i can find a known problem, later in the day

You're extremely kind - thank you. Thanks also to PoD for the other reply above. I'm about to go out and test the readings now....

 

[television]

Nothing known. The duo valve is fed from the K40/2 relay module on the drivers side fuse box. Pin 2 is the common on the Duo valve 1 & 3 being each valve respectivly. pins 6,7,8 are the pins on the K40/2 that connect to the valve

 

[rjsdavis]

The duovalve has 2 valves/cylinders, 1 for each side of the car. The cable to the valve IIRC has 3 pins. One of those pins will be common, perhaps the middle pin (perhaps zero volts, but thats a guess), each of the other 2 pins will control an individual valve.

If neither side of the car is controllable, that suggests to me that at the very least, the common connection on that connector isn't doing anything, because it either isn't connected to the heater control panel for some reason (and likely neither will the other 2 pins be connected), or because the panel is faulty.

Someone will be along shortly to tell you which position the duovalve defaults to when not connected, I have a feeling that it's the fully open (hot) position, it would make sense in an emergency to have it fail on hot.

If someone knows if there is supposed to be a direct connection between the heater panel and the duovalve, then it would be a very simple matter to isolate the pins on the back of the panel, and run some wiring through the window and into the bonnet, to test if things are working properly - but somebody needs to confirm that before you attempt it.

Ok some test results....

FAN - 0, BOTH SIDES MAX COLD
13.95 volts from both valve feeds - steady reading

then went onto

FAN - 5, BOTH SIDES MAX COLD
14.05 volts from both valve feeds - steady reading

then went back to

FAN - 0, BOTH SIDES MAX COLD
14.42 volts (!) from both valve feeds - steady reading

then went onto

FAN - 5, BOTH SIDES MAX HOT
12.91 volts from both valve feeds - steady reading

FAN - 0, BOTH SIDES MAX HOT
14.49 volts from both valve feeds - steady reading

FAN - 5,
NS - MAX HOT - 12.91 volts - steady reading
OS - MAX COLD - 14.06 volts - steady reading

FAN - 0,
NS - MAX HOT - 14.49 volts - steady reading
OS - MAX COLD - 14.49 volts - steady reading

I took these readings from cold - i.e. started the car and took them straight off over a period of about ten minutes whilst she warmed up (I was assuming that the engine temp really shouldn't make a difference to the voltage readings), I am guessing that's this is why the first and third readings have changed - which is slightly strange, as the settings were the same, but this doesn't make sense.

So does anyone know whether these are even close to where they should be? I am not sure that I am heartened by the fact that there are voltage changes at the power connector - but I am finding no difference inside the cabin - i.e. it's always HOT!!

I need to solve this before re-filling the air-con with refrigerant, as otherwise it would be pointless, as the heater would overcome and negate the air-con cool air from making a difference! And it's starting to get warm again now!!!

 

[rjsdavis]

Anyone know if these readings are where they should be - or miles away?

Thanks again

 

[rjsdavis]

Resolved!

The duovalve looks to be a very simple piece of equipment. If you're getting hot air instead of cold, then its obviously not being controlled correctly.

I'd get a multimeter across the 3 terminals on the duovalve wiring connector (duovalve disconnected), and get a friend to adjust the temperature in the cabin - see what voltage changes are evident.

I doubt the heater panel is wired directly to the duovalve, so I would try and trace the connection and test for continuity - my guess (and its a guess) would be that something is wrong with the connection between the two devices (presuming that is, that the heater control panel is working correctly)/
.

The car was recently taken into an air-conditioning specialist, who linked up an aftermarket computer, and went through the stored and current faults.

He cleared a number of faults, including one, which was talking about a communication problem between the heater control panel and a relay.
He also spent some time tapping the duovalve with a mallet. At the time, it appeared to be unresolved, as all during this time, the car was running, and the air didn't get any cooler.

On the journey home, I left the heater off, as I didn't want the hot air getting into the cabin and stiffling me! A couple of days later, I had to demist the screen, and had left the heater on for a while - it occured to me after a while that the cabin wasn't getting hot as usual, and I let the air into the cabin via the face-directed dash vents, AND IT WAS COOL! I couldn't believe it, and I nearly steered off the road in shock!

The air-con guy was the last person to do anything with it, so I am still none the wiser as to whether it was an ECU problem that he cleared, or as simple as beating the duovavle with a mallet - but the end is all I care about at the moment - I just need to refill the refridgerant back into the air-con system, and I will get some nice cool air - just in time for winter!