Giovanni

I replaced all 3 bad actuator under the dash and the a/c is icecold after I bypassed the water valve. When the engine is running with a/c turned off, it pulls a strong vacuum. If the a/c is turned on, there is zero vacuum at the hot water valve. Shouldn't it just be the other way? Please help.....

AO

Yep it should be the other way. Default is open so your windows can never fog up. Sounds like it may be hooked up to the wrong actuator?

the flyin' scotsman

Where are you measuring the strong vacuum? The white vac line from the vac distribution under the central console provides the vac to heater valve; if you've wired the valve closed (per Tonys direction) and plugged the white vac line there should be no heat to the car unless the recirc actuator is stuck to allow warm outside air to enter the cabin.

IcemanG17

Hmm
Need more details.....the heater valve being open and closed is controlled by the solenoids behind the stereo...which is controlled by the climate control head (brain)....in the WSM there is a diagram that shows when the heatervalve is supposed to open (where the temp slider is, flap postion & A/C)...if the car is running, temp on 65 & flaps at center....the heater valve should be closed...which means vacuum should be applied to the heater valve.....if the solenoid fails (mine did) then it will always have vacuum....take a look here for some more details

https://rennlist.com/forums/showthre...acuum+solenoid


Does the heater valve solenoid open-closed (apply vacuum) when it is supposed to.....a simple check is temp at 65....then slide it to max heat....it should open......if your vacuum supply is good...it should work...its possible the white line from the solenoid to the heatervalve has a crack.....that would cause enough of a leak to not close the heatervavle?

AO

BTW, there is a slight delay (5-10 seconds or so) before the vacuum comes on/drops off when you set it at 65 or 85. This drove me nuts. I thought I had a leaky vacuum line before I realized the time delay.

bd0nalds0n

The logic for whether the heater valve should be open or closed is a function controlled by the mixing motor which is located on the driver's side under the pod.

In at least one way that the mixing motor can "fail," the heater valve will remain open (i.e., the heater valve solenoid will never receive power) if the climate control system is on, even with the temperature slider moved all the way over so the "max cool" microswitch is triggered.

It took me forever to solve this problem on my car. If you have good vacuum everywhere with the climate control switched off, but the heater valve opens when you turn the climate control system on, consider swapping the mixing motor.

Giovanni

Thank ya'll. I will bet money toward a bad mixing motor. The valve heat was bought new last winter and it was tested OK last weekend. The white line going to the heater valve holds 30 in hg vacuum when the engine is idling. As soon as I turn the ac on, it looses all vacuum thus allowing hot air, even it I let it idle for a minute or so. I will swap the mixing motor with the one from the 84 and see it solves the problem. You guys are the best.

IcemanG17

Gio
Hmm.....that sounds odd that it looses vacuum after you turn on the A/C......that sounds like a control head problem to me......it has to send an electric signal to the solenoid to turn "ON" the vacuum closing the valve....I would try to sway out the control head with a known workng one before you dig any deeper?

bd0nalds0n

The electric signal you refer to is delivered by the mixing motor.

imfinlay

I had a bad mixing motor (a.k.a. setting motor). It's possible to r&r these. Mine was full of grease and other gack - remove the actuating arm, remove 4 scews holding the cover on that side, clean and reassemble. The other cover on the other side can also be removed and given a blast with switch cleaner.

I had to use the gearbox of mine and a PCB from another one to get a working motor. Pretty easy to do.

If you need, I have a bunch of spare solenoids and the coloured vacuum pipes (not the white one though).

ian

Thaddeus

This thread is confusing me.

Can somebody tell me: the heater valve... if there is no vacuum applied, it remains open, so you have heat. Right? And when you apply vacuum, it closes, and turns off the heat.

Right?

The HVAC in these cars is comical, it's so complex. Mechanical, electrical, pneumatic... all working in concert... sometimes...

WallyP

Don't forget that the heater valve is opened (Yes, Thaddeus - that means no vacuum) when the DEFROST is on, regardless of the temp setting. Sounds as if you might be getting DEFROST instead of A/C.

You can feel and see (with some difficulty) the mixing motor move when you move the temp lever. If it moves only when the temp lever hits the stops on each end, the resistor string (temp lever, outside temp thermistor, inside temp thermistor) is open somewhere - usually at the connector inside the left front fender.

the flyin' scotsman

The design was a default to have heat in the event of a vacuum failure; no vacuum and the heater valve is indeed open and vice versa.

'Comical, complex' and frustrating...............engineered with '70s technology. Perhaps the 'big 4' could develop a new system that works with a high tech approach using todays elctro/mechanical technology.

bd0nalds0n

Boy oh Boy isn't that the truth!

I wonder how hard it would be to retrofit the climate control system from a 944? I think the control panel is much nicer/sleeker, and I loved having the infinitely adjustable defroster/footwell flaps.