Weird heater fault

Captain Crappycrimp · 29th October 2018, 11:24

I have a strange intermittent fault thats driving me crazy. The heater/aircon works sometimes and then for no apparent reason wont work the control panel operates but nothing happens. Ive replaced the resistor for a gold one and the low speed works (when it works). Sometimes turning the car off then on again will get it working sometimes not. If on first starting the car the aircon/heating comes on it will work perfectly until the engine is again turned off then its pot luck if it will work again. It can work for days and weeks at a time then suddenly wont work for a period of hours or days before suddenly deciding to work again.

Hope someone can help now the winter is biting its becoming serious for demisting as when it doesnt work the internal fan wont run so cant demist the car.

Shadomobile

Devilish · 29th October 2018, 11:41

Easiest thing to eliminate first is the ATC control unit, swap it with another.

T-Cut · 29th October 2018, 14:21

Is it the heating or the chilling that doesn't work?
You say the heating/aircon output 'works' sometimes, which doesn't really describe the problem.

There are two independent sections to the climate control system which provide heated and chilled airflows. The aircon buttons regulate how these flows are mixed to give you the selected inside temperature.

The heating side will (should) operate without any part of the chilling system running. The radiator fan is needed for refrigeration, but doesn't affect the heating system, so the resistor issue may not be relevant.

So does it get too hot, too cold or stop blowing alltogether?

TC

SD1too · 29th October 2018, 14:31

Hello Richard,

Just adding to T-Cut's post above, I think I've identified a couple of key clues in your description:

Quote:

Originally Posted by Shadomobile

... the control panel operates but nothing happens .... when it doesnt work the internal fan wont run ....

It sounds to me as if your blower (internal fan) isn't running. This would result in no airflow and consequently little, if any, sensation of heat since your car is a diesel. This would seem to match your report that "nothing happens".

The blower has an electronic speed control module and a very small number of members have suffered a failure. There have also been one or two cases of the blower motor expiring. If you're DIY and electrically minded you can determine which it is yourself. Would you like some details?

Simon

Captain Crappycrimp · 29th October 2018, 19:40

Ok to be more specific

When it works everything works heating and chilling.

When it doesn't work nothing works heating or chilling

The control unit is lit at all times and appears to operate, changes temp on screen fan speed etc but no response from fan.

I do not think the fan has failed as when the system works the fan operates throughout its range and demists very quickly.

In as simple a way as I can put it, the system does not seem to "boot up" correctly when it does not work its as though the signals are not getting from the control unit to the fan or heat and aircon systems

Captain Crappycrimp · 29th October 2018, 19:43

Simon
thanks for the answer yes I would like details please Im not that good with electronics but will have a go.

Thank you

SD1too · 30th October 2018, 07:21

Hi Richard,

I think you have what is known in electronics circles as an intermittent fault.

Try to resist the temptation to apply too much armchair logic involving detailed consideration of the entire electrical system otherwise you'll convince yourself that the car needs scrapping!

What you need to do is some amateur tunnelling. The blower motor speed control module resides on the left hand side of the heating/AC unit close to the bulkhead so it's a case of sticking your head in the passenger footwell. Be prepared for considerable discomfort. You'll probably find a photograph elsewhere on the forum.

First remove the four pin connector and identify the brown and black wires. With the ignition switched off, bridge these two terminals on the connector. Now turn on the ignition and the blower should run continuously at maximum speed. This test can be performed the next time that the system fails you. If the blower runs, suspect the speed control module.

Another thing you can check is that the blower motor relay is seated properly and that its terminals are clean. You'll find this in the engine compartment fusebox labelled with a lovely graphic of fan blades.

Yet another check you can make is that the 40 amp fuse link (10)

supplying the blower motor is screwed down firmly. Disconnect the battery negative cable* before working in this area though as this fuse is live all the time.

* Wait for the sat. nav. disc drive to shut down before disconnecting the battery.

Simon

Groundsman Willie · 30th October 2018, 20:05

Had a similar problem with mine last winter, ATC lit up ok but there was zero response from the fan to either an increase or decrease in the temperature setting. Mine was the under bonnet relay, can't for the life of me remember the number, but it's a yellow one

it's the same type as the heated rear window relay, so I swapped them over and the heating has worked fine ever since. Interestingly, do has the hrw so I guess it was just a bad connection. Worth a try

29th October 2018, 11:24	#1
Captain Crappycrimp Gets stuck in Devil car is dead! Join Date: Oct 2011 Location: Scarborough Posts: 774 Thanks: 94 Thanked 145 Times in 92 Posts	Weird heater fault I have a strange intermittent fault thats driving me crazy. The heater/aircon works sometimes and then for no apparent reason wont work the control panel operates but nothing happens. Ive replaced the resistor for a gold one and the low speed works (when it works). Sometimes turning the car off then on again will get it working sometimes not. If on first starting the car the aircon/heating comes on it will work perfectly until the engine is again turned off then its pot luck if it will work again. It can work for days and weeks at a time then suddenly wont work for a period of hours or days before suddenly deciding to work again. Hope someone can help now the winter is biting its becoming serious for demisting as when it doesnt work the internal fan wont run so cant demist the car. Shadomobile __________________ SAVED SO FAR 2003 Le mans Green MG ZTT 1.8T, 2003 MG ZT CDTI BRG, ZT 190 Typhoon, 2001 Rover 75 1.8 Tourer , 2002 solar red MG ZTT 177, 2005 Silver MG ZTT CDTI, 2001 Trophy Blue MG ZT (Early No 131) 160, 2004 XPG MG ZT CDTI. 2004 MG ZT Ignition Blue MG Press car/Pheonix 4 personal car. Rover 75 CDT top spec Cowley car. 2003 MG ZT 190+ white Gold. Couldn't save MG ZT 1.8T XPG 2005 MG ZTT Goodwood Green(Devil car) MY PROJECT 2004 MG ZTT Diesel auto in disappointing grey.

29th October 2018, 11:41	#2
Devilish This is my second home 75 Tourer Join Date: Apr 2009 Location: Cannock Posts: 4,133 Thanks: 3 Thanked 189 Times in 121 Posts	Easiest thing to eliminate first is the ATC control unit, swap it with another. __________________ If at first you don't succeed, hide the evidence

29th October 2018, 19:40	#5
Captain Crappycrimp Gets stuck in Devil car is dead! Join Date: Oct 2011 Location: Scarborough Posts: 774 Thanks: 94 Thanked 145 Times in 92 Posts	Ok to be more specific When it works everything works heating and chilling. When it doesn't work nothing works heating or chilling The control unit is lit at all times and appears to operate, changes temp on screen fan speed etc but no response from fan. I do not think the fan has failed as when the system works the fan operates throughout its range and demists very quickly. In as simple a way as I can put it, the system does not seem to "boot up" correctly when it does not work its as though the signals are not getting from the control unit to the fan or heat and aircon systems __________________ SAVED SO FAR 2003 Le mans Green MG ZTT 1.8T, 2003 MG ZT CDTI BRG, ZT 190 Typhoon, 2001 Rover 75 1.8 Tourer , 2002 solar red MG ZTT 177, 2005 Silver MG ZTT CDTI, 2001 Trophy Blue MG ZT (Early No 131) 160, 2004 XPG MG ZT CDTI. 2004 MG ZT Ignition Blue MG Press car/Pheonix 4 personal car. Rover 75 CDT top spec Cowley car. 2003 MG ZT 190+ white Gold. Couldn't save MG ZT 1.8T XPG 2005 MG ZTT Goodwood Green(Devil car) MY PROJECT 2004 MG ZTT Diesel auto in disappointing grey.

29th October 2018, 19:43	#6
Captain Crappycrimp Gets stuck in Devil car is dead! Join Date: Oct 2011 Location: Scarborough Posts: 774 Thanks: 94 Thanked 145 Times in 92 Posts	Simon thanks for the answer yes I would like details please Im not that good with electronics but will have a go. Thank you __________________ SAVED SO FAR 2003 Le mans Green MG ZTT 1.8T, 2003 MG ZT CDTI BRG, ZT 190 Typhoon, 2001 Rover 75 1.8 Tourer , 2002 solar red MG ZTT 177, 2005 Silver MG ZTT CDTI, 2001 Trophy Blue MG ZT (Early No 131) 160, 2004 XPG MG ZT CDTI. 2004 MG ZT Ignition Blue MG Press car/Pheonix 4 personal car. Rover 75 CDT top spec Cowley car. 2003 MG ZT 190+ white Gold. Couldn't save MG ZT 1.8T XPG 2005 MG ZTT Goodwood Green(Devil car) MY PROJECT 2004 MG ZTT Diesel auto in disappointing grey.

30th October 2018, 07:21	#7
SD1too Doesn't do things by halves Rover 75 2.5 Connoisseur Auto (1999) Dealer launch model. Join Date: Mar 2007 Location: Former Middlesex Posts: 20,567 Thanks: 1,587 Thanked 3,749 Times in 3,181 Posts	Hi Richard, I think you have what is known in electronics circles as an intermittent fault. Try to resist the temptation to apply too much armchair logic involving detailed consideration of the entire electrical system otherwise you'll convince yourself that the car needs scrapping! What you need to do is some amateur tunnelling. The blower motor speed control module resides on the left hand side of the heating/AC unit close to the bulkhead so it's a case of sticking your head in the passenger footwell. Be prepared for considerable discomfort. You'll probably find a photograph elsewhere on the forum. First remove the four pin connector and identify the brown and black wires. With the ignition switched off, bridge these two terminals on the connector. Now turn on the ignition and the blower should run continuously at maximum speed. This test can be performed the next time that the system fails you. If the blower runs, suspect the speed control module. Another thing you can check is that the blower motor relay is seated properly and that its terminals are clean. You'll find this in the engine compartment fusebox labelled with a lovely graphic of fan blades. Yet another check you can make is that the 40 amp fuse link (10) supplying the blower motor is screwed down firmly. Disconnect the battery negative cable* before working in this area though as this fuse is live all the time. * Wait for the sat. nav. disc drive to shut down before disconnecting the battery. Simon __________________ "Whatever is rightly done, however humble, is noble." Sir Henry Royce.

29th October 2018, 14:21	#3
T-Cut This is my second home Rover75 and Mreg Corsa. Join Date: Nov 2006 Location: Sumweer onat mote o'dust (Sagin) Posts: 21,754 Thanks: 341 Thanked 3,660 Times in 2,924 Posts	Is it the heating or the chilling that doesn't work? You say the heating/aircon output 'works' sometimes, which doesn't really describe the problem. There are two independent sections to the climate control system which provide heated and chilled airflows. The aircon buttons regulate how these flows are mixed to give you the selected inside temperature. The heating side will (should) operate without any part of the chilling system running. The radiator fan is needed for refrigeration, but doesn't affect the heating system, so the resistor issue may not be relevant. So does it get too hot, too cold or stop blowing alltogether? TC

30th October 2018, 20:05	#8
Groundsman Willie Gets stuck in Rover 75 1.8t Join Date: Dec 2017 Location: Newbury Posts: 842 Thanks: 783 Thanked 423 Times in 264 Posts	Had a similar problem with mine last winter, ATC lit up ok but there was zero response from the fan to either an increase or decrease in the temperature setting. Mine was the under bonnet relay, can't for the life of me remember the number, but it's a yellow one it's the same type as the heated rear window relay, so I swapped them over and the heating has worked fine ever since. Interestingly, do has the hrw so I guess it was just a bad connection. Worth a try __________________ Dave