how to fool ambient temp sensor to run heater

Ivessm

2005 140 HighTop Pass
Restarting some comments on this thread. Still shaking my head about why MB would put the 39 degree limit in. :thinking: :thinking:

I'm thinking of the resistor solution and wondering if anyone has actually gotten under the van and traced the wiring from the temp sensor in the front bumper back to where it plugs into what ever it plugs into. I would think it would be easier to tap the wires back near the head unit rather than run wires all the way from the front bumper back to the dash for the resistor override.

Any thoughts?

stew
 

Aqua Puttana

Poly - Thread Finder
Restarting some comments on this thread. Still shaking my head about why MB would put the 39 degree limit in. :thinking: :thinking:
...

Any thoughts?

stew
Gov'mint regulations.

vic
 

4wheels

Member
Restarting some comments on this thread. Still shaking my head about why MB would put the 39 degree limit in. :thinking: :thinking:

I'm thinking of the resistor solution and wondering if anyone has actually gotten under the van and traced the wiring from the temp sensor in the front bumper back to where it plugs into what ever it plugs into. I would think it would be easier to tap the wires back near the head unit rather than run wires all the way from the front bumper back to the dash for the resistor override.

Any thoughts?

stew
I still have this 'mod' and I love it.
The easiest way is to put the switch where the sensor is (if you do not mind the switch in that location )
All you have to do - take off front grille ( 2 screws and 4 plastic buttons , just watch the tabs on the bottom of the grille ) Then cut the wires , yes cut them not tap , and mount the switch , so you can use it with the grille installed .
But then , after you take off the grille - you will see that it is not that hard to run the wires inside , so you can switch it from the driver's seat .
 

Redpillar

Member
I am having issues with my booster heater. It worked last year but now it does not. The weird thing is that while driving and the engine and outside air temperatures are well above the set points the red light on the switch will go on and stay on , if the switch happens to be in the on position. I stopped to see if there was anything coming out of the exhaust and it was cold. If it is below freezing and I start the engine and turn on the booster heater, the red light will go off after about 30 seconds. Any ideas? I have not immersed the temp sensor in ice water yet.
 
It works on my 2016/2017 4x4 170. Dash mounted a DPDT switch but only use it with engine off to fool my Factory Espar D5. Intercepted wires at ambient temp probe using a pair of 2 conductor waterproof connectors. This allows me to revert back to original wire configuration if necessary.


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I'm assuming when you switch back your dash gives you the correct outside temp? What value resistor did you use?
Thanks
 

gltrimble

Well-known member
Yes, the dash reads the outside temperature when switch defaults to the ambient temperature probe. I recall using a 22k resistor which I believe equates to 5 degrees F. This allows the D5 to run for 40 minutes 3 consecutive times for a total of 120 minutes. The owners manual explains how long the D5 will run at various outside temperatures. It is 6 times at 20 minutes, 4 times at 30 minutes, 3 times at 40 minutes, or 2 times at 50 minutes before you need to start the engine. You could install two DPDT switches in series with two resistors to allow multiple temperatures.


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Aqua Puttana

Poly - Thread Finder
... You could install two DPDT switches in series with two resistors to allow multiple temperatures.


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Why not put a resistor in series on one leg and use a switch as a shunt? The "fake ambient" temperature itself isn't critical for monthly operation. It needs to be low enough while still appearing to the computer that the circuit is intact.

NCV3ambientLowTemp.jpg

My apologies for the kindergarten style MS Paint schematic. The general range 15 K resistor is a guess based upon the 22 K being reported as a low spoof. Again, the resistor value/resulting specific temperature is not necessarily critical for monthly test operation. It needs to be low enough.

vic
 
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Aqua Puttana

Poly - Thread Finder
Tried remote control today and it works , too .

10k ohm resistor ( 31* F ) - aux heater will turn off after 20 min.

22k ohm resistor ( 5* F ) - aux heater will turn off after 40 min.

...
Is that a function of the spoofed temperature, or the engine coolant achieving setpoint/cutoff? I don't recall anyone else ever mentioning that [T1N] Espar heater run time duration is related to ambient temperature. Above 39C is an environmental/emissions lockout, not a control point.

vic
 
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Aqua Puttana

Poly - Thread Finder
Espar D5 run times are dependent on outside temperature as mentioned two posts back. All spelled out in owners manual. Total run time and/or number of starts is limited to avoid draining battery. Starting the motor resets the counter.
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Thanks.

Interesting. That's another reason for someone wanting aux heat for a longer time period to spoof the system even when the the ambient temperature is below 39F. Choosing a higher ohm resistor for the modification may be the better choice. Battery drain is a real consideration though.

vic
 

gltrimble

Well-known member
For those that have inquired offline, I settled on a 15k resistor which gave me 40 minutes of run time on the OEM D5 up to three times for a total of 120 minutes. 15k equates to 18F. In most cases 40 minutes is enough to heat my Isotemp 4+ gallons. Cold weather, below 40F, might require a second 40 minute operation.






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Aqua Puttana

Poly - Thread Finder
For those that have inquired offline, I settled on a 15k resistor which gave me 40 minutes of run time on the OEM D5 up to three times for a total of 120 minutes. 15k equates to 18F.
...
Good input. :thumbup:

It appears that you used the SPST shunt with resistor method?

SPSTwithResistor.jpg

vic
 
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NEWFISHER

New member
Not being a wiring genious, I would love to have someome come up with a cut and splice kit to override the 39° switch on feature. I would buy one asap.
 

Aqua Puttana

Poly - Thread Finder
Vic, his pic looks like it could be a DPDT? But I like your SPST diagram. Only question is what wire do you tap for the resistor?
Thanks!
I guess it could be DPDT.

The added resistance just needs to be in series with the sensor. Either wire will work.

vic
 

gltrimble

Well-known member
Vic, his pic looks like it could be a DPDT? But I like your SPST diagram. Only question is what wire do you tap for the resistor?

Thanks!


Bob,

Yes, DPDT. All required parts are shown in the pictures above, 1 DPDT switch, 1 resistor, 4 strand wire, beer is optional. Resistor is connected between your two wires same as ambient sensor. DPDT switch just determines which resistance computer will see, either sensor or resistor.

Others have reported one consequence that I also experienced. Computer is hesitant to return back to ambient temperature as quickly as it switched to my 18F. Eventually it does return.

And thanks for the fantastic day MTB riding, beers, and fish tacos.

Lynn


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vanski

'05 Snow Camper, '17 170 4x4, Adventure Vissionary
Hey there ncv3 folk... Pretty nifty and straight forward mod you guys came up with here. Some of the t1n folks have a thread going to replace the existing factory d5 heater with a new one but the new one has an ambient >39f ambient temp lockout like your factory d5 furnaces do. This resistor should work just as well for us as it has for you, but some of us want to use the furnace with engine off and there’s speculation as to whether it will work without the ecm being on to interpret the sensor information and then broadcasting it over the k line to the heater. It appears some of you are running the furnace with engine off. Does this mean the ecm doesn’t need to be powered on to interpret the ambient temp information and then broadcast? Doesn’t appear anyone is powering on the ecm with the engine off to get this mod to work with the engine off. Perhaps ncv3 and t1n Sprinters are different in that the ecm is always interpreting sensor information (we haven’t tried this so I’m not suggesting this is the case)? Perhaps ours will work just as yours and we don’t need to power on the ecm??
 

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