Installing a heater cut off valve 1988 3.2 cabriolet.

I buried this post in another thread so I thought I'd start a separate one so you guys could see it.
When I picked my car up from its major service at Tim Stanford's in Fort Lauderdale a few months ago, we went on a test drive, car ran great. When we got back to the shop I decided to try the air conditioning, since Tim had installed a new AC compressor for me and recharged the system with R12. The first blast of air that came out of the vents was hot, Tim immediately told me that I had a leak in my heater valve and that they are normally open and only closed when 12 volts gets to them, and that doesn't always do the job. (They leak)
Tim pointed out an area in the engine compartment where I could install a simple ball valve to close the heater loop.
I got a 3/4-in brass ball valve with a bleeder from Ace hardware and installed it in the location shown.
Made a huge difference with my AC, I was getting 49° air before the valve was installed, now I'm getting 39° air!
Added benefit is that this valve has a bleeder at what I think is the highest point of the cooling system. This should make bleeding the air out of the system a lot easier.
I painted the valve flat black so it wouldn't stick out so much in the engine compartment. I also open it occasionally to let some coolant circulate through dow heater circuit heater core, just to limit any corrosion.
Alden
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Some may look askance or look away. But yes, this fix is on my list of things to do. ‘83 QV Cab. Thank you!


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It may not matter to you, you may be one who runs the AC full blast so it would make no difference. The Mondial was the first with climate control instead of AC. You set a temperature and it modulates its operation to achieve that temp. That is done by running the AC and letting small amounts of hot water into the heater to achieve that variation and you have defeated that function. It was the entire purpose of an electric hot water valve. If it was mine Id replace the hot water valve.

 

I know that you are correct Brian, if this leaking valve had been discovered before my major service was completed, I would have asked Tim Stanford to replace it at that time.
And you are also correct about me. Living in Florida, I never use the heat or defrost, but I must get as much as I can out of the air conditioning, especially during the summer! ("Summer" here lasts from March until October, lol!)
I have also read that even when the valve is operating correctly it still lets a little hot coolant leak past, resulting in higher temperatures from the air conditioning. (Mine was 49-52F w/the valve open and 39-42F with the valve turned off)To that end, I'm not really sure if my heater valve is working correctly or not, but it is letting some some heat mix in with the air conditioning so I just shut it off.
I'm happy with the results and the extra bleeder valve too. Plus, it is easily reversible should the need arise.
Thanks for the informed response, Brian. You are a very valued member here!
Alden

 

I have had a TR for many years and disagree 100% about the efficiency of the valve based on testing them for function. . My AC in Texas is almost never set at full cold and its the same system with different sized condensor and evaporator.

 

Every case will be different based on location, weather, humidity, age of systems (including hoses), and owner’s desire for maximum control of car interior atmosphere.

In my case, previously living in coastal HI and now in coastal Southwest, the AC capability was removed years ago (a little more power is nice!), along with the dashboard temp sensor. I want total control of hot water migrating through the cabin.

All situations are different.


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+1 -- and/or check that someone didn't get the hoses swapped either at the hot water valve or in the engine bay. This hot water valve only seals well if the flow direction is correct (i.e., the pressure in the flow helps hold the valve closed).

 

The problem is the heater valves have a solenoid and spring valve inside, with rubber valve seals. The rubber perishes and can leak. There is a rebuild kit available for the plunger, but the spring itself can loose its ability to hold the valve. There are replacement plunger units, but they are made in China and may not have suitable spring pressure. The old plunger units were made in Fance, and used to be available from BMW, but they discontinued the part, or offer the Chinese repelacement.

All would be well if there was a quality remanufactured part, which now appear available, but I am skeptical of the quality of the internal parts used by those making reproduction units.

The sign of the weak spring (assuming the ruber parts are ok) is when your heater output, when controls are set to heat, increases with engine rpm, as noted the coolant flow which rises with rpm itself helps seat the valve if the spring is otherwise weak.