A/C Cooling fan fact check

stocktake · 24th July 2022, 10:20

As some may have read the compressor on my 1999 KV6 auto decided to fail and this weekend was set aside for me to replace it.
I have had the A/C degassed and I have changed the compressor and the condenser. I am waiting to have the A/C regassed.
In the meantime out of curiosity I just had to test the demist setting to see if the rad fan runs even though the A/C is empty.

I can confirm that on my 1999 2.5 KV6 with the engine running, no gas in the A/C when I press the demist button the rad fan springs into life. So, it would appear that previous reports are incorrect?

The compressor does not engage (as you would explect with no gas in the system)

My fan is an original 3 speed 4 wire fan. there are no modifiactions to the fan wiring.

Arctic · 24th July 2022, 10:44

Quote:

Originally Posted by stocktake

As some may have read the compressor on my 1999 KV6 auto decided to fail and this weekend was set aside for me to replace it.
I have had the A/C degassed and I have changed the compressor and the condenser. I am waiting to have the A/C regassed.
In the meantime out of curiosity I just had to test the demist setting to see if the rad fan runs even though the A/C is empty.

Quote:

I can confirm that on my 1999 2.5 KV6 with the engine running when I press the demist button the rad fan springs into life. So, it would appear that previous reports are incorrect?

The compressor does not engage (as you would explect with no gas in the system)

My fan is an original 3 speed 4 wire fan. there are no modifiactions to the fan wiring.

Hi Dave.
I thought we already knew that

from the ones we have tested at the meets, my MGZT 190 did the same when i had the four wire 3 speed fan original when i bought it, and also later when i changed it out for two wire 2 speed, with no gas in.

The fan still need to work to keep the temp down to 100, if it raises above that and bring it down to 91c and so on.

Testing below which i know you have read, others may not have.

https://www.the75andztclub.co.uk/for...87&postcount=1

How did it all go fitting the compressor etc smooth hopefully.

xsport · 24th July 2022, 10:47

yes thats correct. It is highlighted in a very detailed post made by jules a few years ago. its the one with recommendations on how to check the radiator fan on demist, it clearly states this. i knew that this was correct , whilst reading a similar post on here about the "inhibitor" function not allowing the fan to kick in when the system was not gassed. i know that the trinary switch has low pressure and high pressure inhibitor switches , but they only effect the clutch operation. im not sure about the other pressure switch"s function though , as it is supposed to only allow the fan to run over a certain pressure ? ...

it could be something with the way that the aircon control box works when the demist switch is pressed and the heater blower and rad fan are energised in tandem.

stocktake · 24th July 2022, 11:22

It was recently posted on here that on the 2.5 kv6 the rad fan would not come on on demist if the A/C was ungassed. This is just to clarify 1st hand that was incorrect

xsport · 24th July 2022, 11:26

so to clarify. the demist test is only a rad fan test. i would imagine that if demist function was to work properly to clear a screen, then the air con button would have to be pressed into the on position. the demist test states to make sure the aircon is in the off position , so that the rad fan is not compromised by air con peramiters to test its function i would imagine.

SD1too · 24th July 2022, 13:04

Quote:

Originally Posted by xsport

so to clarify. the demist test is only a rad fan test. i would imagine that if demist function was to work properly to clear a screen, then the air con button would have to be pressed into the on position. the demist test states to make sure the aircon is in the off position , so that the rad fan is not compromised by air con peramiters to test its function i would imagine.

No, I am afraid you have drawn the wrong conclusion Stefan.

When the windscreen demist button is pressed (the "demist test") it activates the air conditioning automatically. Because of this, the radiator fan will begin running at slow speed. It is not necessary to make sure that the air con. is in the "off" position beforehand. What is important is that the engine is cold when the test is carried out so that there is no possibility that the fan is already running at a higher speed due to coolant temperature demands.

Simon

SD1too · 24th July 2022, 13:24

Quote:

Originally Posted by stocktake

It was recently posted on here that on the 2.5 kv6 the rad fan would not come on on demist if the A/C was ungassed. This is just to clarify 1st hand that was incorrect

Here is the post by Savestones to which you're referring Dave. It's worth noting that when he mentions "coolant" in the first paragraph he means refrigerant and not antifreeze solution.

I'm not sure that it's safe to conclude that anyone is incorrect. Savestones has a 2002 ZT 2.5 KV6 and you have a 1999 Rover 2.5 KV6. On the face of it the two cars appear to be behaving differently and there may be a reason for this that we haven't yet discovered.

Simon

xsport · 24th July 2022, 14:11

oh i see simon. so the demist test will work with the aircon switch in either the on or off position ? ok , it seems there are a lot of posts on here incorrect , that give people the wrong information , as i do remember reading this in a post, but i can not recall by whom its that long ago. This demist test is really just a slow speed fan operation check then ? irrespective of air con function , and will test the fan slow speed function even if the aircon does not activate ? im glad you have pointed this out , and i think it is better named " the slow speed fan test " ....

xsport · 24th July 2022, 14:19

im pretty sure JULES would have mentioned any differences , with the older versions doing a slow speed fan test but ...

suzublu · 24th July 2022, 14:26

Quote:

Originally Posted by xsport

im pretty sure JULES would have mentioned any differences , with the older versions doing a slow speed fan test but ...

Have you read this? https://www.the75andztclub.co.uk/for...ad.php?t=35567

24th July 2022, 10:20	#1
stocktake Vis Whiz Rover 75 2.5 auto Saloon Join Date: Jun 2007 Location: LEEDS Posts: 20,587 Thanks: 2,057 Thanked 3,056 Times in 1,621 Posts	A/C Cooling fan fact check As some may have read the compressor on my 1999 KV6 auto decided to fail and this weekend was set aside for me to replace it. I have had the A/C degassed and I have changed the compressor and the condenser. I am waiting to have the A/C regassed. In the meantime out of curiosity I just had to test the demist setting to see if the rad fan runs even though the A/C is empty. I can confirm that on my 1999 2.5 KV6 with the engine running, no gas in the A/C when I press the demist button the rad fan springs into life. So, it would appear that previous reports are incorrect? The compressor does not engage (as you would explect with no gas in the system) My fan is an original 3 speed 4 wire fan. there are no modifiactions to the fan wiring. __________________ Dave... Lost a few stones and a Gall Bladder and part of a bile duct and all of my dignity in the suppository incident Last edited by stocktake; 24th July 2022 at 11:20..

24th July 2022, 11:22	#4
stocktake Vis Whiz Rover 75 2.5 auto Saloon Join Date: Jun 2007 Location: LEEDS Posts: 20,587 Thanks: 2,057 Thanked 3,056 Times in 1,621 Posts	It was recently posted on here that on the 2.5 kv6 the rad fan would not come on on demist if the A/C was ungassed. This is just to clarify 1st hand that was incorrect __________________ Dave... Lost a few stones and a Gall Bladder and part of a bile duct and all of my dignity in the suppository incident

24th July 2022, 10:47	#3
xsport Posted a thing or two rover 75 club se Join Date: Apr 2011 Location: Leicester Posts: 1,637 Thanks: 358 Thanked 419 Times in 310 Posts	yes thats correct. It is highlighted in a very detailed post made by jules a few years ago. its the one with recommendations on how to check the radiator fan on demist, it clearly states this. i knew that this was correct , whilst reading a similar post on here about the "inhibitor" function not allowing the fan to kick in when the system was not gassed. i know that the trinary switch has low pressure and high pressure inhibitor switches , but they only effect the clutch operation. im not sure about the other pressure switch"s function though , as it is supposed to only allow the fan to run over a certain pressure ? ... it could be something with the way that the aircon control box works when the demist switch is pressed and the heater blower and rad fan are energised in tandem.

24th July 2022, 11:26	#5
xsport Posted a thing or two rover 75 club se Join Date: Apr 2011 Location: Leicester Posts: 1,637 Thanks: 358 Thanked 419 Times in 310 Posts	so to clarify. the demist test is only a rad fan test. i would imagine that if demist function was to work properly to clear a screen, then the air con button would have to be pressed into the on position. the demist test states to make sure the aircon is in the off position , so that the rad fan is not compromised by air con peramiters to test its function i would imagine.

24th July 2022, 14:11	#8
xsport Posted a thing or two rover 75 club se Join Date: Apr 2011 Location: Leicester Posts: 1,637 Thanks: 358 Thanked 419 Times in 310 Posts	oh i see simon. so the demist test will work with the aircon switch in either the on or off position ? ok , it seems there are a lot of posts on here incorrect , that give people the wrong information , as i do remember reading this in a post, but i can not recall by whom its that long ago. This demist test is really just a slow speed fan operation check then ? irrespective of air con function , and will test the fan slow speed function even if the aircon does not activate ? im glad you have pointed this out , and i think it is better named " the slow speed fan test " ....

24th July 2022, 14:19	#9
xsport Posted a thing or two rover 75 club se Join Date: Apr 2011 Location: Leicester Posts: 1,637 Thanks: 358 Thanked 419 Times in 310 Posts	im pretty sure JULES would have mentioned any differences , with the older versions doing a slow speed fan test but ...