AC Fiasco

[Fordum]

Yep, classic bad ball........

Not sure that yours has a hot water cutoff. I have not seen one on a vehicle is a long time.
Instead, a door just diverts the air around the heater core when you don't want heat.
That is on most vehicles the blend door. When its all the way one way, all the air goes through the heater core.
The other way, the air conditioner evaporator.
In between, you get warmer or cooler air, thus the name blend door. It blends hot and cold air.

 

[Chief Brody]

Yep, classic bad ball........

Not sure that yours has a hot water cutoff. I have not seen one on a vehicle is a long time.

oh yes it does...a little plastic piece with 4 hose connectors and an actuator that the vacuum line attaches to...in the off mode and in Max AC the vacuum is supposed to shut that valve and shut the water off from the heater core...

 

[Chief Brody]

also, on Max AC it is supposed to actuate a door that is visible behind the glovebox lid...on max ac it closes off outside air and recirculates cold cabin air...there isn't enough vacuum right now to open that either...

something is causing a weak vacuum somewhere...and it's got to be a hose...unless the vacuum ball actually "boosts" vacuum.

 

[Fordum]

Interesting.
My '76 Torino had one, as did my '79 F150 and my 66 F600. But my '89 F250 doesn't, and I have not seen one in years.
I remember reading somewhere that if you designed the water flow through the engine with that in mind, it caused problems when you turned it off.

So, they just let it run through the core and turned the air off.
I know that everytime I have had to bypass a heater core, I always used a connector fitting so that the water would flow instead of just plugging the lines.

In your case, with the 4 lines, it still flows when the heat is off, it just bypasses the core.
Another problem with those valves, was that they were bad about sticking due to lack of use.
If you can reach it, you might try helping the actuator a little with the engine idling with good vacuum.
Or you could pull the line off and plug it and then just tie the valve closed.

 

[Fordum]

The ball just stores vacuum unless you see a wire going to it. In which case its a vacuum pump.
Never saw one of those on anything but a diesel though.

Sounds like either the "switch" is bad, seen that before, or you have a vacuum leak somewhere.
On my '79, everything was real slow, and I had to get going and then snatch my foot off the gas to boost the vacuum enough sometimes.

Finally realized I could hear hissing from the "switch" that controlled the functions. Took it out, and it was a silicon maze that a stainless steel plate slid back and forth over with holes to direct the vacuum.

The rivet that held it together and acted as a pivot was loose and the tension spring was not doing its job. I took it apart, cleaned every thing up and lightly lubed it with some Vaseline.
I think I used a bolt and nylock nut to put it back together so I could adjust the seal tension.
Never had a problem after that.

 

[Chief Brody]

I need a 60cc syringe so I can attach it to a piece of vacuum line, then to the heater control valve...that would test it..
but it is so hot I have to wear thick gloves in there...it is a mere couple inches from the exhaust manifold and it gets hot...I tested with a piece of rubber vacuum hose and it melted...it requires that hard emissions hose.

I could deal with a manual shutoff valve...no need for heat around here till January...

 

[Blue85]

If the heater core lines are the same size, you just loop one line back to bypass it or substitute a small U-bend underhood.

A mighty-vac is handy for finding vacuum leaks. Some stuff can be found with a bit a compressed air, but you want to keep the pressure low to keep from damaging stuff. A stethoscope with an open tube end is nice for finding the leak. There is probably a single line running from underhood to the underdash HVAC section. Try to find that and separate whether the leak is underhood or underdash.