how to fool ambient temp sensor to run heater

K-9 SPRINTER

Well-known member
This is for (2007-2013)
I run both my aux (MB OEM 5K +5K) espar heaters (as well as my aftermarket D4 Espar)at least once a month
this is how I get around the MB lockout of 39° for the factory installed Espars. I have a 2010
the sensor is under the back of front license plate, in the center,and snaps right out and in:thumbup:

I fill a cup with ice and water (mostly ice) and place the sensor in it,

For 2014 MB moved the sensor and its not as easy to get to
2014 the sensor is https://sprinter-source.com/forums/showpost.php?p=325484&postcount=8
 

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flman

Okay wait for it....... Red Herring cop out!
If you could wire in a potentiometer you could dial in any temp you want right from the drivers seat.
 

smiller

2008 View J (2007 NCV3 3500)
Just for anyone interested a common 10k ohm resistor results in a dash temperature readout of 31 degrees F (on my 2008.) The sensor has a negative temperature coefficient so if you want a colder reading use a higher resistance value.

I'd like to exercise my Espar auxiliary coolant heater but the lockout on that seems to be based on coolant temperature, not OAT. Does anyone know where the coolant temp sensor is located?
 

flman

Okay wait for it....... Red Herring cop out!
Just for anyone interested a common 10k ohm resistor results in a dash temperature readout of 31 degrees F (on my 2008.) The sensor has a negative temperature coefficient so if you want a colder reading use a higher resistance value.

I'd like to exercise my Espar auxiliary coolant heater but the lockout on that seems to be based on coolant temperature, not OAT. Does anyone know where the coolant temp sensor is located?
I would think all you need to do is have your 10k resistor in place, and start the engine cold should be enough to get the Espar running?
 

smiller

2008 View J (2007 NCV3 3500)
I would think all you need to do is have your 10k resistor in place, and start the engine cold should be enough to get the Espar running?
That didn't seem to work. I had the resistor in place and my dash readout said 31F, but my coolant temp was about 75F (ambient temperature at the time) and I think the Espar needs to see a colder coolant temp in order to start (IOW the system sees a relatively warm coolant temp and says 'you don't need auxiliary coolant heat right now.') It does work AFAIK, or at least it did last winter.
 
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K-9 SPRINTER

Well-known member
Just for anyone interested a common 10k ohm resistor results in a dash temperature readout of 31 degrees F (on my 2008.) The sensor has a negative temperature coefficient so if you want a colder reading use a higher resistance value.

I'd like to exercise my Espar auxiliary coolant heater but the lockout on that seems to be based on coolant temperature, not OAT. Does anyone know where the coolant temp sensor is located?
if you had less than 1/4 of a tank of fuel, they will not run

Ive been running my heater monthly for years with the ice , never a problem (highest outside ambient temp was 92)2010 was the 1st yr to have the 39* lockout
.... and I check both MB espars and the remote.
1st I put the sensor in the ice water, then check the temp on dash , when it reads below 39, I use the remote to turn on 1st espar , once I see it fires up and is running, I shut it off with the dash switch. then I start the engine, and use the dash switch to turn on both and look to see that both espars are running , and let them run about 10 minutes
 
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smiller

2008 View J (2007 NCV3 3500)
Well I dunno. My fuel tank was nearly full so it wasn't that. I have only the auxiliary diesel coolant heater (not cabin heater) so maybe that makes a difference. I guess I'll just see if it starts working again when it gets colder out and if so then I'll know there was some condition I wasn't meeting during the test. :idunno:
 

K-9 SPRINTER

Well-known member
looks like you only tried it with the resistor ..... try it with the ice water...
let it cool the temp below 39, then start the engine, then switch it on
 

smiller

2008 View J (2007 NCV3 3500)
But there's no difference between bringing the thermistor to the desired resistance value with ice water or using a fixed resistor, it's all the same to the computer.
 

4wheels

Member
Fired up my heater booster today with a 22k oHm resistor . ( 5* F at 22k oHm )
As soon as I disconnected the resistor , the heater booster turned off .
Was trying to turn on the AUX heater , but it did not work , I think I need to read the manual .
 

4wheels

Member
Well I dunno. My fuel tank was nearly full so it wasn't that. I have only the auxiliary diesel coolant heater (not cabin heater) so maybe that makes a difference. I guess I'll just see if it starts working again when it gets colder out and if so then I'll know there was some condition I wasn't meeting during the test. :idunno:
The temperature knob has to be on HEAT
 

4wheels

Member
Hardwired a switch today with a 10k ohm resistor . The switch located where the battery switch is .
Was able to turn on the AUX heater with a pre set time . It works ! It heats the coolant and the cabin ! :thumbup:
Still need to try the remote control.
 

smiller

2008 View J (2007 NCV3 3500)
The temperature knob has to be on HEAT
Bingo, you win the prize. Spoofing the OAT reading with a resistor and turning the temperature selector to the heating range results in the Espar coolant heater operating as expected.

Since in my option package the Espar heater only assists in getting the coolant up to temperature when the engine is running and isn't really intended to assist with cabin heat (AFAIK) I'm not sure why it cares what the HVAC is doing, but in MB's infinite wisdom it is thus. I do have the 'auxiliary heat' HVAC option but as I understand it that is an electrical assist and not related to the Espar system.
 

4wheels

Member
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.

Sorry global warming propaganda , but the MB's manual says :

Turn on the aux heater at least once a month for approx. 10 min. The aux heating could otherwise be damaged !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 

smiller

2008 View J (2007 NCV3 3500)
Spoofing the OAT reading with a resistor and turning the temperature selector to the heating range results in the Espar coolant heater operating as expected.
Just a note, today I noticed that the Espar auxiliary coolant heater will come on even without the resistor trick... all you need is to have the HVAC set to the heating range and off you go. The OAT and coolant temperatures were both 71F but as long as I had the HVAC temp control in the heat range (and the auxiliary coolant heat dash switch turned on of course) then the Espar unit would come on. So actually it's easy to exercise it regularly regardless of the season.
 

4wheels

Member
Just a note, today I noticed that the Espar auxiliary coolant heater will come on even without the resistor trick... all you need is to have the HVAC set to the heating range and off you go. The OAT and coolant temperatures were both 71F but as long as I had the HVAC temp control in the heat range (and the auxiliary coolant heat dash switch turned on of course) then the Espar unit would come on. So actually it's easy to exercise it regularly regardless of the season.
Tried it and it did not work . Tried AUX heater with timer and remote control - did not work . Same for heater booster .
 

smiller

2008 View J (2007 NCV3 3500)
Tried it and it did not work . Tried AUX heater with timer and remote control - did not work . Same for heater booster .
Interesting, must be some difference in our two configurations (my package is simpler than yours, consisting of only the coolant heater function.) But mine was definitely running, it was quite audible and there was heat coming from the exhaust.
 

K-9 SPRINTER

Well-known member
Just a note, today I noticed that the Espar auxiliary coolant heater will come on even without the resistor trick... all you need is to have the HVAC set to the heating range and off you go. The OAT and coolant temperatures were both 71F but as long as I had the HVAC temp control in the heat range (and the auxiliary coolant heat dash switch turned on of course) then the Espar unit would come on. So actually it's easy to exercise it regularly regardless of the season.

Interesting, must be some difference in our two configurations (my package is simpler than yours, consisting of only the coolant heater function.) But mine was definitely running, it was quite audible and there was heat coming from the exhaust.
......... you have a 2008, dont you?

the 39° lockout started in 2010..
https://sprinter-source.com/forums/showthread.php?t=13252
 
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johnshmit

Well-known member
I've paid for the rear heat (H13) rear a/c and top of the line cluster just for that - preheat with a timer.
But my brilliant salesman put HZ9 on it and quit.
Now when i ask the dealer to change SCN code to H12 they just hang and have to be restarted.
I've updated my great Chinese DAS Xentry tool, but it does not support C3 MUX and face-lifted Sprinter.
So for ~$700 I can get new tool or independent Espar.:thinking:
Cannot makeup my mind yet.

At the mid time I'm thinking about connecting CAN sniffer between heater and Sprinter and if I can identify heater related communications I can spoof them and lie to the heater. I have a full house of parts to do that.
 
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