Disable the cooling fan

flyer_phil · 23rd May 2010, 11:27

Ok my CDT has a duff thermostat, and now the warm weather is here and not withstanding I have the bottom air intakes blocked off, it now runs at pretty much the correct temperature ie gauge in middle and around 78 - 80 indicated on test 7. Good. I may go and see Dr Jules when winter arrives again.

However, due to the hot weather I had the air con recharged (Kwik fit £49), but of course, when operating the air con the damn cooling fan comes on permanently which of course sends the engine temperature plummeting once more. Do we really need this function on our cool running diesels? Is there any way to disable this function ie permanently on with the air con, yet maintain its function when its realy needed - ie when the engine temperature becomes too hot say 100 degC ?

I dont have a wiring diagram for the car. I suppose it would be simple to just disconnect the feed from the air con switch that operates the cooling fan - could even replace with a manual switch on the panel.

Any ideas??

Thomas · 23rd May 2010, 11:52

yep dont ! lol you could quite easily cook the compressor and then you would be looking at a rather large bill !

T-Cut · 23rd May 2010, 12:03

You need a speed-sensitive switch to trip the fan when you go below say 10mph.
It should also be ambient temperatutre sensitive, so the trip speed depends on how warm the weather is.
Anything else is a recipe for disaster.

TC

flyer_phil · 23rd May 2010, 12:17

Quote:

Originally Posted by Thomas1983

yep dont ! lol you could quite easily cook the compressor and then you would be looking at a rather large bill !

Ok so are you saying that the radiator cooling fan cools the compressor also?

I thought the reasoning behind the fan coming on with the air con was that because the compressor puts extra load on the engine, then extra cooling is needed.

I used to have a Pontiac Firebird which had a huge AC compressor, when switched on the engie RPM used to drop 300 - 400 RPM the load was so great - and this had a 300 ft Llbs of torque V8 !

James.uk · 23rd May 2010, 13:43

>>>Ok so are you saying that the radiator cooling fan cools the compressor also? <<<

YES!!!

The compressor will overheat and seize up without the fan running..

...

T-Cut · 23rd May 2010, 19:21

Quote:

Originally Posted by flyer_phil

Ok so are you saying that the radiator cooling fan cools the compressor also?

Not directly. It cools the condenser matrix located at the bottom of the radiator. This allows refrigerant vapour to cool and so condense back into a liquid. If that doesn't happen, the vapour gets hotter and hotter by being passed through the compresser. The compressor then overheats and you can have big trouble.

TC

suffolk boy · 24th May 2010, 00:29

Quote:

Originally Posted by T-Cut

Not directly. It cools the condenser matrix located at the bottom of the radiator. This allows refrigerant vapour to cool and so condense back into a liquid. If that doesn't happen, the vapour gets hotter and hotter by being passed through the compresser. The compressor then overheats and you can have big trouble.

TC

err without wishing to appear rude would it not be a good idea to change the thermosat ? unless it envolves taking the car apart or most off it they fitted for a reason unless i have gone mad ! which buy the way is quite possible !

flyer_phil · 24th May 2010, 08:58

Hi

Thanks for all your replies.

Of course you are correct, its the thermostat that needs replacing. Its just such a terrible job to do and very expensive. I was trying to delay it until the winter when it will be essential.

I'm almost tempted to sell the car and buy one with a functioning thermostat. This car seems to have a never ending things to do list, fuel pumps, thermostats, engine mounts, resonating fuel lines, O rings PCV valve, EGR, MAF sensors, then if the clutch goes thats £700 alone.

I think I'll go and buy a Volvo S60 diesel.

SD1too · 24th May 2010, 09:14

Quote:

Originally Posted by flyer_phil

Ok so are you saying that the radiator cooling fan cools the compressor also?

Quote:

Originally Posted by T-Cut

Not directly. It cools the condenser matrix located at the bottom of the radiator. This allows refrigerant vapour to cool and so condense back into a liquid. If that doesn't happen, the vapour gets hotter and hotter by being passed through the compresser. The compressor then overheats and you can have big trouble.

Excellent explanation T.C.

Simon.

T-Cut · 24th May 2010, 11:31

Quote:

Originally Posted by wedd

err without wishing to appear rude would it not be a good idea to change the thermosat?

Quote:

Originally Posted by flyer_phil

Of course you are correct, its the thermostat that needs replacing. Its just such a terrible job to do and very expensive. I was trying to delay it until the winter when it will be essential.

That's the only solution to the OP's dilemma about running aircon and engine at the same time. It would in simple terms, return normality.

TC

23rd May 2010, 11:27	#1
flyer_phil Loves to post Rover 75 CDT Classic, 2003, Moonstone Join Date: Mar 2008 Location: Chesterfield at the moment Posts: 411 Thanks: 0 Thanked 1 Time in 1 Post	Disable the cooling fan Ok my CDT has a duff thermostat, and now the warm weather is here and not withstanding I have the bottom air intakes blocked off, it now runs at pretty much the correct temperature ie gauge in middle and around 78 - 80 indicated on test 7. Good. I may go and see Dr Jules when winter arrives again. However, due to the hot weather I had the air con recharged (Kwik fit £49), but of course, when operating the air con the damn cooling fan comes on permanently which of course sends the engine temperature plummeting once more. Do we really need this function on our cool running diesels? Is there any way to disable this function ie permanently on with the air con, yet maintain its function when its realy needed - ie when the engine temperature becomes too hot say 100 degC ? I dont have a wiring diagram for the car. I suppose it would be simple to just disconnect the feed from the air con switch that operates the cooling fan - could even replace with a manual switch on the panel. Any ideas??

23rd May 2010, 11:52	#2
Thomas This is my second home MG6 1.8T GT SE Join Date: Mar 2009 Location: Falkirk Posts: 9,510 Thanks: 106 Thanked 173 Times in 128 Posts	yep dont ! lol you could quite easily cook the compressor and then you would be looking at a rather large bill !

23rd May 2010, 12:03	#3
T-Cut This is my second home Rover75 and Mreg Corsa. Join Date: Nov 2006 Location: Sumweer onat mote o'dust (Sagin) Posts: 21,753 Thanks: 341 Thanked 3,660 Times in 2,924 Posts	You need a speed-sensitive switch to trip the fan when you go below say 10mph. It should also be ambient temperatutre sensitive, so the trip speed depends on how warm the weather is. Anything else is a recipe for disaster. TC

23rd May 2010, 13:43	#5
James.uk Passed Away 2002 Pale Blue. Rover 75 CDTi Connoisseur auto. 170K miles Join Date: Dec 2008 Location: Near the M67. Posts: 14,509 Thanks: 199 Thanked 585 Times in 397 Posts	>>>Ok so are you saying that the radiator cooling fan cools the compressor also? <<< YES!!! The compressor will overheat and seize up without the fan running.. ...

24th May 2010, 08:58	#8
flyer_phil Loves to post Rover 75 CDT Classic, 2003, Moonstone Join Date: Mar 2008 Location: Chesterfield at the moment Posts: 411 Thanks: 0 Thanked 1 Time in 1 Post	Hi Thanks for all your replies. Of course you are correct, its the thermostat that needs replacing. Its just such a terrible job to do and very expensive. I was trying to delay it until the winter when it will be essential. I'm almost tempted to sell the car and buy one with a functioning thermostat. This car seems to have a never ending things to do list, fuel pumps, thermostats, engine mounts, resonating fuel lines, O rings PCV valve, EGR, MAF sensors, then if the clutch goes thats £700 alone. I think I'll go and buy a Volvo S60 diesel.