Attention 94-97 owners, I have a favor to ask. Can anyone tell me whether the water control valve found on the 94 and newer models. works to shut off water flow throgh the heater core?
Here is a picture of the valve in question:
If so, my next question would be where does the vacuum pickup line go? I have an older model without this feature and have often wondered about rigging something to prevent hot water from circulating through the heater core when desireable, i.e. when A/C is on.
Sorry it took so long to look this up, but here's what I know. I can only assume that the valve shuts off the water flow through the heater core, otherwise, why would it be there? The wonderful schematic in the factory service manual is far from a true schematic, so it's not much better than useless. Another thing that makes me think it shuts off the water is that the cooling system bleed procedure tells you to turn the heater to high to make sure all air is out.
Preventing the hot water from going through the core might be of little value since the blend door should prevent airflow through the heater core and instead should direct the airflow through the A/C evaporator. But, there could be some leakage past the blend door which could degrade the A/C performance.
The vacuum line for this valve comes from one of the dials for the climate control (I can't remember which, I've slept since I looked it up). Your '91 may have the slider controls rather than the rotary dials that my '95 has so you may not be able to retrofit the valve without changing the controls.
Mikeman,
Thanks for taking the time to research and reply. I also posted this on the Heating,Cooling A/C forum and received a nice reply from a knowledgeable Ford tech.
In the interim, I did go ahead and install the valve between the heater core hoses during a recent core swap. Installation was easy, but there is not a good deal of room for the valve. Presently it resides alongside the accumulator/drier. The vacuum line was easily spliced into the same line that controls the vacuum motor for the outside air door that is active for MAX A/C. Most auto parts stores carry a 1/8in, plug in style T fiiting.
According to the Ford tech, the reason for the valve is as you surmised, to reduce heat convection within the shared plenum box. Of course after the conversion the weather cooled off and I haven't been able to really test the system under extreme heat.
So, if I understand correctly, the coolant flow through the heater core is stopped whenever you are on MAX Cool. That seems like a logical place to tie it in the vacuum line.
As far as testing, you could go to MAX Cool and then run the temp slider to it's hottest setting. Then you should get re-circulated air only with no cooling. Is that correct? The blend door sends air through the heater core not the evaporator. The MAX Cool setting causes the fresh air door to be closed. The water control valve stops the hot coolant from going through the heater core. Thus you get re-circulated air without heat or cooling. What do you think?
An idea that comes to mind now is: What happens when your engine starts to overheat and you want to cool the engine as quickly as possible. I have found it necessary to run the heater in a pinch. So with my 96 I not only need to turn on the heat but also turn off the A/C (not a bad idea).
This may seem obvious but, with my Miata it's a different story. There are two radiator fans. One operates on engine temp. The other runs only when the A/C is on. So if I turn off my A/C during stop and go traffic I loose half the air flow through the radiator. So which is worse, loss of air through the radiator or the added load of the compressor. Just another thing to think about when the needle starts climbing.
tom,
Good suggestion on how to test. I'll give it a try. You have the concept, however on MAX A/C with the TEMP selection on HOT, there would be recirculated air, the evaporator would continue to provide cold air - there would just be no hot water to the heater core - thus no convected or radiated heat around the plenum.
Several months earlier, while working on the heater core, I was surprised to find the heater core was active when the A/C was on. That core gets so hot you cannot keep your hand on it. I could not see how that flimsy temp blend door could possibly prevent considerable heat from seeping across to the other side where the cold air was circulating. That started the bypass thought process and then I discovered later model years had a bypass valve.
As to overheating, (knock on wood) that has never been an issue. On the contrary, the engine rarely goes above "N" on the hottest of days. The only times I've seen it move were due to a bad fan clutch and again with a leaking radiator cap. With the present bypass valve setup, every setting other than MAX A/C permits water circulation through the heater core. With the vacuum line plumbed to the outside air door motor, the bypass valve is only active when MAX A/C is selected.
Last edited by aerocolorado; 09-05-2003 at 05:03 PM.
Tom,
Yes, your suggestion on testing worked well. The valve is in place and operates well. In fact, while testing, the heater core developed a leak and by having the valve in place, the core could be bypassed using the MAX A/C setting.
I also had to recently replace a clogged orifice tube. After recharging the A/C, it blows almost too cold now (~34-36 degrees). Leaving the thermometer in the vent while driving and using the diverter valve shows neglible differences in vent temps. I suspect if you have warmer vent temps of 40 or above, heater core diversion may have a greater effect.
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