p38 heater problems

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tommo138

tommo138

New Member
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541
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braintree, essex
ive been searching on here to see if i can find out whats up with my heater, the symptoms are that the if you try to adjust the temperature it simply wont go cold! at any point it will stay hot unless you drop it right down to low then it will start to be cold, everything else with it seems to be working fine,if anyone has any advice it would be a great help.
 
just had another good look over it and have found the following, if you run the heater with air con off the temp will not change from being very hot, but there is no book symbol, if you run with air con on or on auto then the book symbol appears but everything is working apart from this temp issue.
 
Ive had this fault in the past and it dissapeared after I replaced both the heater matrix temp sensor (one that clips to the coolant pipe) and the evaporator temp sensor (one that pushes into the hole at below the matrix sensor).

I diagnoised the fault with my Faultmate though so it wasn't too bad for me. I would see if you can get a hook up and get the faults read and go from there. If that doesn't show anything then you want to look at the live data displays of the HeVAC sensors. Im pretty sure you will find one of the sensors reading some stupidly high or low value causing the problem you are describing.

-Wills :)
 
hi, thanks for that was thinking it might be a blend motor! are the two sensors easy to replace, if not ill have to book it in and have it looked at as i dont have any software for it. Thanks again.
 
I've got a 2001 P38 with the same symptoms - only blows hot (no bad thing in this weather), although the book symbol is now showing.
If I buy and change the two sensors mentioned do you think it will fix it or does in need recalibrating/tuning in some way once fitted?
Thanks,
Steve
 
Wills is right, diagnostics would highlight any failed sensors-pointless buying something you don't need. Have a look at the post "Strange" by Sticks first and try the tips in there.
Regarding your second question-No, you can't calibrate sensors, only blend and blower motors, sensors are just "Plug & play"
 
what does the book thing on the heater display mean i had this once before but as soon as i turned the ignition off and on it went thanks
 
The book symbol indicates that a fault is logged in the HEVAC system. The unit does a self check and for intermittent faults it will sometimes clear them. However if the fault crops up again, it will bring the symbol up again. Usually the faults are related to sensor problems, Blend motor feedback relating to position or low refrigerant pressure
 
could it be that when i done the head gaskets i took the air con pips off (doh) and it de pressurised it self everywhere and i have not yet had it refilled (due to bloody cold weather).
 
its only ever apeared once breafly for 5 mins then i turned off and on again and never seen it again since, coolent in the header was a bit low though due to leaking pip,dont know about before as i brought the car with blown head gaskets (w reg vouge for 1,700 at the famous 80,000) seems all the head gaskets go about then ,thought it was a bargin really and has been fine ever since apart from a leaking hose but not the end of the earth.
 
My heater is now blowing very hot on the drivers side, no matter what heater settings I use, but it does blow cold on the passenger side if I turn temp down.
Any ideas?
Cheers,
Steve
 
Looks like the drivers side blend motor has stuck open. Put the HEVAC in Manual mode and try taking the drivers side temperature down to LO and up to HI a few times to see if it will clear the fault. You should hear the blend motor run as you change the temp. If that doesn't work, you will probably have to change the motor. They come in a set of 3 and I would advise replacing the set. Word of advice-don't be tempted to buy second hand, you could finish up in the same boat soon after. Look on here Range Rovers for more on HEVAC and blend motors.
 
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