Webasto airtop 2000stc cooling before re-cycling

S

Skyliner123

Member
Hi all,
Our T6 has a Webasto airtop 2000 stc diesel heater fitted complete with the external temperature sensor and runs from the rotary dial. When we run it on around the 3rd marker on the dial it heats the van up to around 21C and then slows down the fan and then stops altogether. Without touching it again it will cut back in again but only when the temperature has dropped to around 14C (I have an internal temperature and humidity product close by the Webasto temperature sensor so can see the rough temps). Is this normal as I would have thought it would kick back in before dropping that much?

cheers
 
It shouldn't be shutting off completely when the temp has been reached, it should gradually drop the heat output down to 0.9Kw as it reaches the set temp on the rheostat. It should then remain at that level until the temp drop makes the output rise again. My 1st thought is that you are setting the rheostat too low - for 21 degrees you should be at the top end of the 4th segment - see diagram below.
At what height is the external temp sensor mounted and are you a high top or raised pop top? Also is the sensor mounted where there is free air circulation - not in a corner or anywhere where sunlight or other heat sources can affect it.
Where is the air for heating drawn from - standard front driver's step?

rheostattemps.jpg
 
Thanks for the reply. T6 with poptop and I have attached a photo showing the position of the dial and temp sensor (above sink in standard side cupboard’s conversion).

The inlet vent is on the drivers step and the unit is mounted outside underneath, all installed by a ‘Webasto’ approved installer and van converter. I bought it privately after the conversion.

I was wondering if the temp sensor was faulty, I did take it off earlier in the year and checked resistance with temperature changes and it did seem to change but didn’t have a reference to check against.

IMG_7690.jpeg
 
Last edited:
The temp sensor isn't in a very good position it is in a corner where the air doesn't circulate fully. ( and sunlight could affect it also ) That is a bit of a dead zone. It needs to be out in the main area where air can circulate around it easily. Mid height in the van is the recommended height - will be higher with the pop top. My sensor is mounted at shoulder height in my high top van.

The installer goofed by placing it there! There are installers and there are installers who think about what they are doing!
Sensor position and incorrect rheostat setting is the fault here. 99% certain.

Sensor is unlikely to be faulty. Just on 10 KΩ at 20 deg C. NTC.
 
Ok many thanks for the feedback. Shoulder height would not work in the van with pop-top and as you know space is at a premium in a t6 especially when the bed is out as not much air moving anywhere but I could try repositioning a bit. Why would it cause it to stop and not maintain a temperature i.e it is losing 7-8 degrees before coming back in and you mentioned it shouldn’t stop at all?

We do find it hot in the van with it running and would prefer 19-20 degrees but if set lower it doesn’t seem to cut back in at all unless you then increase the dial then it comes straight back on without repriming.
 
Skyliner123 said:
Ok many thanks for the feedback. Shoulder height would not work in the van with pop-top and as you know space is at a premium in a t6 especially when the bed is out as not much air moving anywhere but I could try repositioning a bit. Why would it cause it to stop and not maintain a temperature i.e it is losing 7-8 degrees before coming back in and you mentioned it shouldn’t stop at all?

We do find it hot in the van with it running and would prefer 19-20 degrees but if set lower it doesn’t seem to cut back in at all unless you then increase the dial then it comes straight back on without repriming.
Click to expand...
Just an afterthought, could it be overshooting the set temperature due to its position making it stop rather than maintaining a temperature? Then switching back on when it thinks it is at the correct temperature which would possibly explain why the temperature on my thermometer (which is probably getting some of the direct heat blown onto it from the heat blower vent) is reading high and it is kicking back in at around 13-14 degrees?

We are away at the moment so I have had plenty of time to ponder this one, just tried to get behind the temperature sensor to see if I could temporarily move it across to where the thermometer is positioned but alas after emptying the cupboard behind it and removing a false panel (much to the missus disgust) I have found that the installer has very neatly wrapped self amalgamating tape around the rheostat and temp sensor wires up to the top so no spare to move it and the tape is wrapped from the top and I don’t have anything to separate it with me!
 
Skyliner123 said:
Thanks for the reply. T6 with poptop and I have attached a photo showing the position of the dial and temp sensor (above sink in standard side cupboard’s conversion).

The inlet vent is on the drivers step and the unit is mounted outside underneath, all installed by a ‘Webasto’ approved installer and van converter. I bought it privately after the conversion.

I was wondering if the temp sensor was faulty, I did take it off earlier in the year and checked resistance with temperature changes and it did seem to change but didn’t have a reference to check against.

View attachment 219227
Click to expand...
Gosh me @Skyliner123 , you're the only person I've seen with a Bay2 conversion apart from me! They put my temperature sensor in a similarly non suitable position like yours, making temperature control shall we say difficult! Mine seems to be either on or off, works well but usually too warm! Air Top 2000 STC again.
I would love to find a good 'tinkerer' like @oldiebut goodie near the midlands to change that basic rheostat for a more useful thermostat possibly telestart?
Any advice gratefully received!
 
@oldiebut goodie don't the Webasto heaters with an external temperature sensors shut down completely like the Eberspacher with an 801 controller?

My Eberspachers with 801s and external sensors always shut down completely and restart when the room temp drops below the set temp but not at full boost (normally at medium output) however they always overshoot the set temp by two (ish) degrees before switching off.

I agree with the incorrect location of the controller, mine is well back in the habitation area and quite high up. The heater outlet is from under a front seat blowing backwards.

Mine is fitted like this in a high roof LWB T6.

1705534431550.png
1705534455755.png
 
Drive Wayne said:
Gosh me @Skyliner123 , you're the only person I've seen with a Bay2 conversion apart from me! They put my temperature sensor in a similarly non suitable position like yours, making temperature control shall we say difficult! Mine seems to be either on or off, works well but usually too warm! Air Top 2000 STC again.
I would love to find a good 'tinkerer' like @oldiebut goodie near the midlands to change that basic rheostat for a more useful thermostat possibly telestart?
Any advice gratefully received!
Click to expand...
I moved mine to the position recommended by @oldiebutgoodie and it has made it better when I tested it in that it now tracks the temperature more inline with the chart and doesn’t seem to cut out anymore. I have only tested it on the drive so far so cannot confirm what an overnight will do but definitely great advice given .
How are you finding your conversion? I didn’t organise the conversion but bought it from the lad that did and think the quality on ours is great. I have spoken to them a couple of times for advice on the phone and found them helpful.
 
rod_vw said:
@oldiebut goodie don't the Webasto heaters with an external temperature sensors shut down completely like the Eberspacher with an 801 controller?

My Eberspachers with 801s and external sensors always shut down completely and restart when the room temp drops below the set temp but not at full boost (normally at medium output) however they always overshoot the set temp by two (ish) degrees before switching off.

I agree with the incorrect location of the controller, mine is well back in the habitation area and quite high up. The heater outlet is from under a front seat blowing backwards.

Mine is fitted like this in a high roof LWB T6.

View attachment 225900
View attachment 225901
Click to expand...
Modern heaters shouldn't switch off as they reach the set temperatures, they should just gradually adjust the heat output downwards to the minimum output and then gradually increase it as the temperature falls below the set point. This prevents the continual cycling of the heater on and off and consequent high battery drain.
They should only switch off if you start adjusting the set point wildly and the set point is exceeded at the lowest output. Usually happens if you use boost setting for too long.
Eberspacher manual description:

Control in heating mode
During heating mode, the room temperature or the temperature
of the hot air drawn in is constantly measured. If the temperature
is higher than the temperature preselected at the control unit, the
control starts.
The heating output is controlled continuously, so that fine adjustment
of the heat flow supplied by the heater to the heat requirement is
possible. The fan speed and fuel quantity correspond to the respective
control stage.
If the set temperature is still exceeded in the smallest control stage,
the heater goes to the “OFF” stage with the fan running on for
approx. 4 minutes to cool down. Then the fan continues at minimum
speed (circulation mode) or is switched off (fresh air mode) until the
heater is started again.
 
Interesting info from the latest models manual:

Risk of undercooling!
The heater does not replace a temperature-monitored and
controlled heating system, which ensures that a constant temperature
is maintained and thus ensures survival in adverse weather
conditions. It is not suitable for the continuous heating of vehicle
interiors at low outdoor temperatures.

Make of that what you will!
 
oldiebut goodie said:
Interesting info from the latest models manual:

Risk of undercooling!
The heater does not replace a temperature-monitored and
controlled heating system, which ensures that a constant temperature
is maintained and thus ensures survival in adverse weather
conditions. It is not suitable for the continuous heating of vehicle
interiors at low outdoor temperatures.

Make of that what you will!
Click to expand...
Was that Webasto or Eberspacher info Oldie?
 
oldiebut goodie said:
Modern heaters shouldn't switch off as they reach the set temperatures, they should just gradually adjust the heat output downwards to the minimum output and then gradually increase it as the temperature falls below the set point. This prevents the continual cycling of the heater on and off and consequent high battery drain.
They should only switch off if you start adjusting the set point wildly and the set point is exceeded at the lowest output. Usually happens if you use boost setting for too long.
Eberspacher manual description:

Control in heating mode
During heating mode, the room temperature or the temperature
of the hot air drawn in is constantly measured. If the temperature
is higher than the temperature preselected at the control unit, the
control starts.
The heating output is controlled continuously, so that fine adjustment
of the heat flow supplied by the heater to the heat requirement is
possible. The fan speed and fuel quantity correspond to the respective
control stage.
If the set temperature is still exceeded in the smallest control stage,
the heater goes to the “OFF” stage with the fan running on for
approx. 4 minutes to cool down. Then the fan continues at minimum
speed (circulation mode) or is switched off (fresh air mode) until the
heater is started again.
Click to expand...
No at all how my recent (latest is six years old) Eberspachers work and I've had two or three the same over the past ten years.
They have been D2 Airtronics supplied by either PF Jones or Bowers as kits with 801 modulators. I've inserted an extra wire inserted in loom to enable external thermostat as per Ebersapcher wiring diagram. I have always wired 801 controllers as per this diagram installing the optional wire shown as 'Optional * Pin 12' on that diagram and below is how they operate when done like this.

Normal operation.
  1. Press heat button and ensure the temperature setting is as desired, in our case normally 16 degrees.
  2. Heater does its diagnosis and starts up and runs up to full boost output then unless ambient temp is very low soon slows down to a high medium output.
  3. When the 801 is registering a room temperature of approximately two degrees above the setting it gradually shuts down eventually to a stop.
  4. When the room temperature drops below the 801 (thermostat) setting the heater restarts and runs up to a medium output.
  5. The heater then loops through items 3 & 4 continuously until switched off.
I have had the heater switched on and running like this for many days at a time either in our UK winters or when in cooler parts and times of summer holidays. I've never had sooting-up problems with mine.
 
That isn't how they are supposed to work! You are putting a far greater drain on your battery if it is switching off and restarting. Yours sound like they are acting as old style thermostats rather than heat modulation via the set point of the controller. Maybe it is because you are using boost setting so you are rapidly heating and are running considerably higher than the setpoint. Have you tried them without using the boost on them?
Eberspachers are a pain!

( PS - it isn't an external thermostat, it is an external temperature sensor namely an NTC thermistor )
 
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