Water control valve to heater on A/C cars

narc · Oct 22nd, 2010, 14:46

Just had a bit of a disaster last night, albeit a minor one with no apparent damage. I had just arrived at my son's ATC unit to collect him when clouds of steam erupted from under the bonnet. On inspection (in the dark!) it was obvious that a hose had gone back towards the heater inputs. SWMBO came and picked us up and I went back to the car today.
Now I had assumed that it was the heater hose that had gone but when i (finally) managed to get the hose clip off the block under the inlet manifold and removed the hose the problem became apparent, there is a vacuum operated valve controling the inlet to the heater matrix which had a large hole in it (it is hidden under the distributor cap so I had not noticed it in the dark). Now I assumed that when I bypassed this valve with a bit of copper pipe as a get home measure that I would have had only hot air coming from the heater but that was not the case, so question is what is this valve for and why is it vacuum controlled? I am more used to the non A/C bulkhead mounted valve which obviously restricts the flow of hot water to the matrix by a rotating spectacle blind, the AC version has me stumped.
All help gratefully received!

Best Regards

Ian

NI_Volvo_Nut · Oct 22nd, 2010, 15:09

It is the heater control valve, I would say the heater matrix is air locked, hense no hot air

narc · Oct 22nd, 2010, 16:00

NI_Volvo_nut,

Perhaps I didn't phrase the question well, I know its the heater control valve, but I can still get hot or cold air via the A/C so I am wondering what purpose the vacuum control mechanism to this HCV has and where it comes from. I guess my question is how does this system work.

Best Regards

Ian

CTCNetwork · Oct 22nd, 2010, 16:07

Hi,

The control valve controls the flow of coolant though the matrix.
However, as the matrix is fed initially from the water pump and then feeds back to the engine (via that control valve) you can still get hot water flowing through the matrix.
You just can't stop the flow.

Des. . .

narc · Oct 22nd, 2010, 16:23

CTCNetwork,

Back to the original question, since without the valve I cannot restrict the flow of hot water to the matrix why can I still turn the A/C down and not have hot air in the cabin (but have hot if I turn it up) and what/where does the vacuum unit do/come from? It obviously opens/closes the valve but it is not controled by the normal wire you have on the Non A/C cars so it obviously is tied into the A/C system somewhere. I would just like to know how the bits work.. I intend to replace the valve anyway.

Best Regards

Ian

CTCNetwork · Oct 22nd, 2010, 16:58

Hi,

Aircon and ECC on the later 940/960/90 versions, as you point out, use vacuum control to direct your air from the distribution box (which is below the heater matrix) and also control the flow of hot coolant through the matrix.
Hence you should hear a slight hissing when you change the direction of the flow of air as the vacuum control will operate the distribution box.
Hence also why some people will hear hissing in car when they have a damaged or broken vacuum pipe.

I assume that the AirCon part can still supply cooler air independently of the Matrix but I suspect if you popped your hand under the dash the box which the matrix sits in will be pretty hot!!

Des. . .

gpl1968 · Oct 22nd, 2010, 17:29

I had the same problem recently although on my car the metal end of the valve was perforated by rust and was weeping slowly.

When I made a temporary fix with a piece of copper pipe, I too found that the heater controls still worked.
The heater control valve is designed to control the flow of coolant to the heater matrix. I'm not sure why the heater controls worked (albeit only for one day in my case) when the valve was effectively fixed open.

I decided to replace the valve with a Scantech unit: Part Number: 51.7896, mainly as it was £18 from Braydons as opposed to a best price of £64 for the Volvo part.
I did re-use the vacum diaphragm though, as it had a better action and fits perfectly on the Scantech valve.

terrywilde07 · Oct 22nd, 2010, 20:00

I too have had a leaking heater control valve and ordered one today from Braydons, I did have Heater matrix problems (it was leaking too) but replaced it today, easier than I thought, only took 6 hours

(from 10am to 4pm) with a 1 hour lunch break (5 'on the job' hrs)... I did bypass the Matrix completely for 2 weeks as I didn't have the time to do the job straight away nor did I want more coolant under my carpets... they weren't to bad, only damp when pressed so I got a wet/dry vaccum on them, come up a treat too

but as the HCV is leaking I have bypassed it with a straight hose connector (not copper tube) so I can have cool air or warm air by using the Air Con to control the cabin temperature... should only take 10 mins to fit it when it arrives

that's the entire cooling system changed in over the last 2 years, Rad, Matrix, all hose's etc, hopefully it'll hold its water now...

and quite pleased with the Matrix swap... no left over screws, no air lock, no squeaks, no rattles, no skin off my knuckles... but more importantly, no broken bits taking it apart or refitting it all... jobs a good un...

Clan · Oct 22nd, 2010, 21:37

the heater system on this car has air mixing for heat control . a flap mixes hot and cold air together before going to the cabin , so in normal use this water valve is always open and hot water is always flowing through the heater radiator even when cold air is selected ....
When you turn the AC on the vacuum valve shuts off the hot water supply to the cabin , this takes away a heat source in the car so makes the Cooling more efficient ... So you can safely bypass this valve with a piece of pipe .

Easy Rhino · Oct 23rd, 2010, 07:01

I was recently held accountable by my stupidity on this item.

For my 12+ year old V90 (3.0 24V) I refreshed the cooling system earlier this year at about 115K miles, and cheaped out on the heater control valce due to cost.

Duh.

The "cheap" replacement valve lasted less than a year, stranding me. Overall, the total cost including the costs of missing a day's work and a Volvo OEM replacement valve was over &700 USD.

Never again. Put a good replacement valve in there.

Oct 22nd, 2010, 14:46	#1
narc Junior Member Last Online: Jul 19th, 2013 12:53 Join Date: Sep 2009 Location: Aberdeen	Water control valve to heater on A/C cars Just had a bit of a disaster last night, albeit a minor one with no apparent damage. I had just arrived at my son's ATC unit to collect him when clouds of steam erupted from under the bonnet. On inspection (in the dark!) it was obvious that a hose had gone back towards the heater inputs. SWMBO came and picked us up and I went back to the car today. Now I had assumed that it was the heater hose that had gone but when i (finally) managed to get the hose clip off the block under the inlet manifold and removed the hose the problem became apparent, there is a vacuum operated valve controling the inlet to the heater matrix which had a large hole in it (it is hidden under the distributor cap so I had not noticed it in the dark). Now I assumed that when I bypassed this valve with a bit of copper pipe as a get home measure that I would have had only hot air coming from the heater but that was not the case, so question is what is this valve for and why is it vacuum controlled? I am more used to the non A/C bulkhead mounted valve which obviously restricts the flow of hot water to the matrix by a rotating spectacle blind, the AC version has me stumped. All help gratefully received! Best Regards Ian

Oct 22nd, 2010, 15:09	#2
NI_Volvo_Nut Volvologist Last Online: Dec 6th, 2023 11:13 Join Date: Aug 2008 Location: Bangor - Norn Iron View Photos By: NI_Volvo_Nut	It is the heater control valve, I would say the heater matrix is air locked, hense no hot air __________________ What's the matter with the car I'm driving? Can't you tell that it's out of style? Should I get a set of white wall tires? Are you gonna cruise the miracle mile?

Oct 22nd, 2010, 16:07	#4
CTCNetwork Forum Support Team Join Date: Dec 2004 Location: Liège, Belgium View Photos By: CTCNetwork	Hi, The control valve controls the flow of coolant though the matrix. However, as the matrix is fed initially from the water pump and then feeds back to the engine (via that control valve) you can still get hot water flowing through the matrix. You just can't stop the flow. Des. . . __________________ Density:- Not just a measurement ~ It's a whole way of Life.! ! ! I drive a Volvo, Please Don't Get In My Way! OldVolvos4Ever He shows up. People die. He vanishes. People should not be afraid of their governments. "He'll deliver more justice in a weekend than 10 years of your Governments should be afraid of their people... "V" courts & tribunals. Just stay out of his way." "I plan to."

Oct 22nd, 2010, 16:58	#6
CTCNetwork Forum Support Team Join Date: Dec 2004 Location: Liège, Belgium View Photos By: CTCNetwork	Hi, Aircon and ECC on the later 940/960/90 versions, as you point out, use vacuum control to direct your air from the distribution box (which is below the heater matrix) and also control the flow of hot coolant through the matrix. Hence you should hear a slight hissing when you change the direction of the flow of air as the vacuum control will operate the distribution box. Hence also why some people will hear hissing in car when they have a damaged or broken vacuum pipe. I assume that the AirCon part can still supply cooler air independently of the Matrix but I suspect if you popped your hand under the dash the box which the matrix sits in will be pretty hot!! Des. . . __________________ Density:- Not just a measurement ~ It's a whole way of Life.! ! ! I drive a Volvo, Please Don't Get In My Way! OldVolvos4Ever He shows up. People die. He vanishes. People should not be afraid of their governments. "He'll deliver more justice in a weekend than 10 years of your Governments should be afraid of their people... "V" courts & tribunals. Just stay out of his way." "I plan to."

Oct 22nd, 2010, 17:29	#7
gpl1968 VOC Member Last Online: May 5th, 2024 23:42 Join Date: Jun 2007 Location: Wirral View Photos By: gpl1968	I had the same problem recently although on my car the metal end of the valve was perforated by rust and was weeping slowly. When I made a temporary fix with a piece of copper pipe, I too found that the heater controls still worked. The heater control valve is designed to control the flow of coolant to the heater matrix. I'm not sure why the heater controls worked (albeit only for one day in my case) when the valve was effectively fixed open. I decided to replace the valve with a Scantech unit: Part Number: 51.7896, mainly as it was £18 from Braydons as opposed to a best price of £64 for the Volvo part. I did re-use the vacum diaphragm though, as it had a better action and fits perfectly on the Scantech valve. __________________ Gavin 1997 945 CD (B230FK) [RIP: 1991 945 Turbo (B230FT) 1992 945 SE turbo (B200FT)]

Oct 22nd, 2010, 16:00	#3
narc Junior Member Last Online: Jul 19th, 2013 12:53 Join Date: Sep 2009 Location: Aberdeen	NI_Volvo_nut, Perhaps I didn't phrase the question well, I know its the heater control valve, but I can still get hot or cold air via the A/C so I am wondering what purpose the vacuum control mechanism to this HCV has and where it comes from. I guess my question is how does this system work. Best Regards Ian

Oct 22nd, 2010, 16:23	#5
narc Junior Member Last Online: Jul 19th, 2013 12:53 Join Date: Sep 2009 Location: Aberdeen	CTCNetwork, Back to the original question, since without the valve I cannot restrict the flow of hot water to the matrix why can I still turn the A/C down and not have hot air in the cabin (but have hot if I turn it up) and what/where does the vacuum unit do/come from? It obviously opens/closes the valve but it is not controled by the normal wire you have on the Non A/C cars so it obviously is tied into the A/C system somewhere. I would just like to know how the bits work.. I intend to replace the valve anyway. Best Regards Ian

Oct 22nd, 2010, 20:00	#8
terrywilde07 Senior Member Last Online: Aug 31st, 2015 03:01 Join Date: Apr 2007 Location: chesterfield	I too have had a leaking heater control valve and ordered one today from Braydons, I did have Heater matrix problems (it was leaking too) but replaced it today, easier than I thought, only took 6 hours (from 10am to 4pm) with a 1 hour lunch break (5 'on the job' hrs)... I did bypass the Matrix completely for 2 weeks as I didn't have the time to do the job straight away nor did I want more coolant under my carpets... they weren't to bad, only damp when pressed so I got a wet/dry vaccum on them, come up a treat too but as the HCV is leaking I have bypassed it with a straight hose connector (not copper tube) so I can have cool air or warm air by using the Air Con to control the cabin temperature... should only take 10 mins to fit it when it arrives that's the entire cooling system changed in over the last 2 years, Rad, Matrix, all hose's etc, hopefully it'll hold its water now... and quite pleased with the Matrix swap... no left over screws, no air lock, no squeaks, no rattles, no skin off my knuckles... but more importantly, no broken bits taking it apart or refitting it all... jobs a good un... __________________ Current: 05 Mercedes C55 AMG, 97(R) V40 1.9 TD, 02(51) S40 S Past: 86(C) 360 GLT, 93(K) 940 Wentworth, 95(M) 440 Si, 94(L) 940 Wentworth, 91(J) 460 GLEi Auto, 98(R) S90 Executive II

Oct 22nd, 2010, 21:37	#9
Clan Experienced Member Last Online: Today 12:51 Join Date: Jun 2007 Location: L/H side	the heater system on this car has air mixing for heat control . a flap mixes hot and cold air together before going to the cabin , so in normal use this water valve is always open and hot water is always flowing through the heater radiator even when cold air is selected .... When you turn the AC on the vacuum valve shuts off the hot water supply to the cabin , this takes away a heat source in the car so makes the Cooling more efficient ... So you can safely bypass this valve with a piece of pipe . __________________ My comments are only based on my opinions and vast experience .

Oct 23rd, 2010, 07:01	#10
Easy Rhino Senior Member Last Online: Nov 1st, 2015 20:39 Join Date: Nov 2007 Location: Kailua, HI	I was recently held accountable by my stupidity on this item. For my 12+ year old V90 (3.0 24V) I refreshed the cooling system earlier this year at about 115K miles, and cheaped out on the heater control valce due to cost. Duh. The "cheap" replacement valve lasted less than a year, stranding me. Overall, the total cost including the costs of missing a day's work and a Volvo OEM replacement valve was over &700 USD. Never again. Put a good replacement valve in there.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)