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Good morning Brickboarders,
Now that the heater core on my '94 940 is successfully replaced, I've turned my attention to an apparently non-functioning heat valve. I can't feel any vacuum at the line that controls the valve. Operating the heat control at the MCC makes no difference.
I read on another post that the valve is only closed during engine warm-up and is normally open after that (regardless of whether you're using heat), and that the amount of heat delivered to the passenger compartment is controlled elsewhere. Is this accurate?
What happens if I eliminate the valve?
Failing that, should I try running a new vacuum line from the MCC to the valve?
Thanks,
Monty
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Past: '79 245, '91 240, '88 245. Current: '90 245, '83 245, '95 940
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The aftermarket valves do not hold up in my experience. So I am going Volvo part for my next valve in the spring.
The original valve lasted me 15 years, the aftermarket replacement, two years.
I have run w/o the valve during the winter months with no ill effects but get a new one on there in time for A/C weather.
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1999 E320 1994 F150 1989 560 SL 1986 560 SL (deceased) 1988 300 TE (departed) 1994 945T (daughter's) 1988 244DL (it lives!) 1986 242Ti (fallow) 1968 GT500KR (under restoration)
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Do you mean the heater water valve? This controls only the flow of hot water to the heater core. The vacuum source is the back of the HVAC controller unit and it is on when the unit calls for heat.
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See the 700/900 "FAQ" at the menu bar top screen left side.
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Steve,
As I understand it, it's the ECU that opens the heater valve once the engine warms up, and remains open regardless of whether you're calling for heat. The heat control on the MCC operates a flap in the heater box and nothing else.
So, if I understand correctly, once the engine warms up, you've got water through the heater core at all times.
Maybe it's better for the life of the heater core to keep it wet?
Monty
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Past: '79 245, '91 240, '88 245. Current: '90 245, '83 245, '95 940
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Nope, it's the HVAC temperature control selector that operates the vacuum to the water valve. The valve is open except when the temp switch (the slide selector or the rotary knob) is set on "cold" setting or if the a/c selector is on "max". In both the latter cases the valve is closed to water flow. The engine ECU has nothing to do with it, nor does coolant temperature. Your problem is a failed valve or a broken vacuum line. BTW, the valve has a limited lifetime, is subject to sudden fracturing, and if it breaks your coolant is gone within about 45 seconds. Not good, so replace the valve for peace of mind.
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See the 700/900 "FAQ" at the menu bar top screen left side.
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Steve,
At the moment, the new core is in and I'm hooked up without a heater valve. It blows nice and hot, with no apparent leaks, and with the temp control turned to Cold, it blows ambient temp (maybe slightly warmer).
So, I'm good for the moment. In fact, I'm feeling pretty great!
Here's the thread I referred to:
http://www.brickboard.com/RWD/index.htm?id=656751&show_all=1
Monty
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Past: '79 245, '91 240, '88 245. Current: '90 245, '83 245, '95 940
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Never mind, I answered my own question. The existing heater valve has obviously never worked since I've had the car, with no apparent ill effects. So, for the moment anyway, I'm gonna ditch it, hook up to the new heater core and see what I've got.
As soon as I remove the whole stinkin' intake manifold to install new heater hoses.... It never ends 8-)
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Past: '79 245, '91 240, '88 245. Current: '90 245, '83 245, '95 940
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