A/C question

Steel Steeds · Sep 9, 2008

I'm agonizingly close to finishing up the full rebuild on my '78, now that the summer is almost over...

I'm ready to reinstall the heater hoses, and have a question for anyone out there with a fairly original II with factory air conditioning: Is there some kind of vacuum actuated solenoid on one of the hoses?
I have a solenoid of this type on my Bronco, to keep hot water from recirculating through the heater core when you are using the a/c. I saw an item on eBay a while back that looked to be the same basic unit, and the seller listed it as a Mustang II solenoid, but provided no info on it. I'm curious if the II came with that item. Anyone have one?

Wart · Sep 9, 2008

Steel Steeds said:
I'm curious if the II came with that item.

Yes, my V6 had one.

Anyone have one?

NFS

rufus13 · Sep 9, 2008

I have all of the original a/c from my '76. I will look in the garage tomorrow and see if I can find it.

I'm in Chicago.....

Steel Steeds · Oct 15, 2008

Still working on this, almost finished under the hood. I was hooking up the vacuum lines to the carb last night, and hooking up the Autometer vacuum gauge, when I came across a rogue line. The car is a '78 which had factory a/c, and just above the heater core lines is where two vacuum lines come out: a very small one and a medium sized one. The medium sized one goes to a funky T, looks like it might have a check valve with one line going to the can in the fender and the main one going to the carb.

But, what is the small one? Mine looks like it was cut and/or burned on the exhaust, the end is all crunchy and misshapen. I got under the dash, but haven't followed it all the way to the end yet. Could this line be the one that was meant to go to the valve mentioned above?
Can someone take a look at their car and give me some guidance here?
Thanks!

Wart · Oct 17, 2008

Golly its been a long time since I've seen a factory carb set up from the factory.

Far as the "valve mention above', the hot coolant shut off valve, no, this hose DOES NOT go to this valve. This valve is operated via vacuum hose from the heat/AC control valve in the dash.

I believe the hose in question,the one coming from the small port of the carb, is ported vacuum and goes to the vacuum advance.

It could also run to the air pump/pumped air control valve, been a looong time since I've seen one of those , too.

But that hose would run to a thermal valve first. And golly, that vacuum should also go to the EGR (another thing I haven't seen in quite a while) in a round about way.

Are you subject to under hood inspection? Around here they just make sure there is a cat, and then emission testing only applies to vehicles 25 years old and newer.

Steel Steeds · Oct 17, 2008

No, no, you misunderstood. I have absolutely nothing remaining of the factory intake/carb system. I've got a Weiand Stealth manifold with a Holley 770 cfm Street Avenger bolted to the top of it, all mounted to a '74 351W.
The vacuum line I'm talking about does seem to come from the heater control area. I couldn't follow it 100%, but it heads that way. It runs together with a larger line, they are wrapped together all the way from under the driver's side dash to the passenger side firewall above the heater core. At the firewall, they enter a specialized grommet, and emerge on the other side separately. The larger of the two is hooked up to full manifold vacuum through a ported "T" which I think is basically a one-way valve. The smaller one went nowhere but down behind the engine where it was burned. The car is a manual tranny, so it has nothing to do with an AT, so I'm guessing it was supposed to be for a water valve and am just looking for some verification from anyone who has a similar setup.

Wart · Oct 18, 2008

Steel Steeds said:
At the firewall, they enter a specialized grommet, and emerge on the other side separately. The larger of the two is hooked up to full manifold vacuum through a ported "T" which I think is basically a one-way valve.

I can just about see the "T" ..

Yes, there is a check valve, and I believe your correct with it having an integral check valve. There is a check valve on manifold vacuum somewhere.

Man Vac goes into the base of the T, one branch goes to the Vac can behind the right fender, the other branch goes to the Heat/AC control. You have probably already figured out the check valve is there so when the throttle opens and the MAP climbs the heater box does not return to it's spring loaded default position of Defrost. Lots of fun driving one of these cars with a faulty or missing check valve.

Also, the vac cans tend to rot out.

And, Oh yeah, the HVAC control tends to "leak". LOL. Oh well ...

The smaller one went nowhere but down behind the engine where it was burned.

Its my guess the valve went bad, or someone replaced the heater hose, and this particular tube was left hanging because it wasn't pulling vacuum because the HVAC control wasn't set to AC so the hose was left to hang because ... For whatever reason. Then the vac tube laid on the exhaust manifold or tube and there you go, a hanging charred tube.

I'm guessing it was supposed to be for a water valve and am just looking for some verification from anyone who has a similar setup.

I'm guessing thats a good guess.

Quick verification of theory is, set the HVAC control to AC, suck on the larger tube and the smaller tube should pull air, then set the control to any other position, suck on the larget tube and hte smaller tube should NOT pull air, as the only time the water valve should be closed is when the AC in operating.

OTOH, see the above about the HVAC control leaking.

I shouldn't laugh, if its possible to love a car I love these cars, but, DamN, they do have their quirks.

Steel Steeds · Oct 19, 2008

Wart said:
And, Oh yeah, the HVAC control tends to "leak". LOL. Oh well ...

I'm guessing thats a good guess.

I shouldn't laugh, if its possible to love a car I love these cars, but, DamN, they do have their quirks.

Yeah, I seem to remember a constant hissing sound when this car was running, so I'm fairly sure there's a leak under the dash somewhere. I couldn't find anything obvious in a visual check.

The heater hoses that the previous owner put on this car were something else. A cobbled together mess of pieces of metal pipe with random sections of hose. Weird. One piece of metal had a flange on it like it should maybe bolt to a valve cover, but it wasn't. I guess I'll just plug that hose until I can round up another of those valves. I'm not putting the a/c in right now anyway.

Yup, I love these stupid cars too...

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