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techie1961
10-19-2009, 11:20 PM
I have an '06 that has had a weird issue since new. It has been to the dealer a couple of times but with this being a work truck, I can't leave it very often.

The issue is that in the winter months when I need the heat (Toronto Canada) I can only get full heat or no heat. The fan switch works fine but if I turn the temperature control a bit off the bottom position, I get roasted in the cab. I have made due on the highway by shutting off the fan altogether and the small amount of air transfer is usually okay unless it is really cold.

When I use the truck in the summer (cold mornings etc.) the heater works fine and you can adjust the temperature fine. It is only when it gets really cold. I don't think that it is the control knob as it seems to work unless it is cold out. Is there a sensor that could be acting up?

Any ideas are appreciated as winter is coming again. I need ideas that I can check on my own as I can't leave the truck for any extended period of time.

mendonsy
10-20-2009, 12:19 AM
This is out of the service manual. It's not a whole lot of help.:idunno:
A/C HEATER CONTROL
DESCRIPTION:
This ATC system uses a combination of electrical and mechanical controls. These controls provide the vehicle operator with a number of setting options to help control the climate and comfort within the vehicle. The A/C-heater control panel is located on the instrument panel inboard of the steering column and below the radio. The A/C-heater control panel contains a rotary-type temperature control knob, a rotary-type mode control knob, a thumbwheel-type blower motor speed control and an air conditioning compressor push button switch and indicator lamp. The A/C-heater control panel also features a push button switch and indicator lamp for the residual engine heat utilization (REST) function, cabin heater or the heater booster (as equipped). The A/C-heater control panel cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.
OPERATION:
To control the interior temperature, the A/C-heater control module uses the actual values from the temperature sensors and the CAN bus and compares them with the nominal value of the temperature control switch. The A/C-heater control panel is serviced only as complete unit and cannot be repaired. If faulty or damaged, the entire control panel unit must be replaced.

sikwan
10-20-2009, 12:27 AM
The issue is that in the winter months when I need the heat (Toronto Canada) I can only get full heat or no heat. The fan switch works fine but if I turn the temperature control a bit off the bottom position, I get roasted in the cab.

Do you have the Espar (aux heater or heater booster) running?

At least in my 06, when the Espar is running, it's full heat when it's at the 5-6 position. When the Espar is off (heat coming from engine now), I can at least get some temperature regulation.

Where the HVAC knobs are, you'll see a rectangular plate (right off the center (vent control) knob) that has a little vent hole. Behind it is a small little fan that sucks air through to a thermistor. The temperature change is not immediate as readings from the thermistor is from the ambient cab air. The heat output will start to decrease once the readings start to equalize.

I think the only way to fix it, and it's a theory, is to reroute the thermistor so that it sits at an output vent, that way the close loop system is more accurate to adjustments and not to the cab temperature.

Aqua Puttana
10-20-2009, 01:02 AM
techie1961,
This is a shot in the dark. I believe I recall reports of vacuum tubing cracking/splitting or other vacuum leaks causing problems. I would take the time to look at the vacuum related components. If that's the problem the fix is generally inexpensive. Did I mention it's a shot in the dark? Hope this does some good. AP/vic

techie1961
10-20-2009, 01:21 AM
Thanks to all three of you that have responded. Tomorrow, I am going to check out some of the ideas.

I have thought that there must be some sort of mode that it goes into when the temperature is colder outside. I wonder if the A/C shuts down below a threshold of some sort. It is almost as if, there is a winter mode and summer mode.

techie1961
10-20-2009, 01:22 AM
Do you have the Espar (aux heater or heater booster) running?

No, I don't use it very often and it is definitely off.

bc339
10-20-2009, 07:00 PM
For what it's worth, I also had the same issue. I have an '04 158 High Roof passenger and this happened to us in '06. Also in the winter, went full hot with the slightest movement of the temp control knob, aux heater off. Fortunately, it was under warranty - the entire control panel was replaced. Sisnce then, it's working like it should. The technician had seen a few others do the same thing and the only repair is to replace the entire control system.
Bruce

Aqua Puttana
10-20-2009, 11:07 PM
Bruce,
Please don't take this the wrong way.:thumbup: Your comment that "the only repair is to replace the entire control system." may be true for a dealership. They are under different constraints. When the vehicle leaves the shop it needs to work, warranty reimbursement doesn't cover "repairing" components, and there are other things that need to figure into how they repair things. I'm not saying it's a right or wrong response, it's just my observation of reality.

There may be less expensive repairs available to a DIY or independent mechanic. Just for an example, Mean in Green (Simon) posted a cable tie cable fix to his heater control.

Single post here:
http://sprinter-source.com/forum/showpost.php?p=41523&postcount=28

Original thread here:
http://sprinter-source.com/forum/showthread.php?t=2058

I'm not saying that MIG's fix applies here, it's just an example that there are other alternatives for repair that you would not accept from a dealership doing warranty repairs on your vehicle. Entire assembly replacement may not be necessary for a DIY owner to repair a problem.

Hope this does some good. AP/vic
For what it's worth, I also had the same issue. I have an '04 158 High Roof passenger and this happened to us in '06. Also in the winter, went full hot with the slightest movement of the temp control knob, aux heater off. Fortunately, it was under warranty - the entire control panel was replaced. Sisnce then, it's working like it should. The technician had seen a few others do the same thing and the only repair is to replace the entire control system.
Bruce

bc339
10-21-2009, 05:00 PM
AP, no offense taken. True, while under warranty, I'd leave it to their repair for the fix. After it runs out, I'd do the same and fix it myself, find a used one at a salvage yard or web search the control p/n for a better price. If you can get any of the numbers off the control unit, check with an auto A/C supplier.