mj1pate

after knocking down major refreshes this summer, I discovered that applying vacuum to the hvac unit, via the manifold vacuum results in a direct vacuum leak. Replacing manifold vacuum with mitivac vacuum in the vacuum source line very near the hvac controller and vacuum manifold, I verified that vacuum applied there just leaks.
From the vacuum source point of view, what places in the hvac controller or vacuum manifold does source vacuum connect to? I have a direct vacuum leak at the point that source vacuum terminates at the vacuum controller/manifold. That's what i need to solve. Thanks

mj1pate

I should mention that my suspicion is that the vacuum source connects directly to the vacuum manifold (solenoids), which if I understand correctly, directs vacuum to all the vent diaphrams and also to the heater valve. But if that is correct, then a vacuum manifold solenoid is capable of metering vacuum intensity to the heater valve. If all the aforementioned is correct and not rubbish, then the vacuum leak is directly in the vacuum manifold and its solenoids? Thoughts? Is this another one of those little $400 2 oz parts?

mj1pate

Oh, but wait... More search may be making me smarter. And maybe not. None of my air control diaphragms work and all vents are stuck "open". So, I blinded off all the vacuum manifold solenoid outputs except for the heater valve solenoid vacuum years ago. If the heater valve solenoid is only one that I require to work, then I can direct vacuum only to that solenoid and see if I still have a leak. If that solenoid is the leaker, then Am I able to swap vacuum solenoids so that the heater valve solenoid is a functional one?

StratfordShark

The vacuum source does connect directly to the solenoids, but the solenoids are switched by controller/mixing motor.

The important thing is to establish whether you have a leak (or leaks) and where.

Now you have access to the vacuum manifold, just work through each actuator. Disconnect each actuator line from manifold and see if the actuator holds vacuum.

All the little solenoid cubes can be removed from manifold, held by single small bolt.With no power applied, you can also see if the solenoids hold vacuum or not.

After checking actuators and solenoids you will have complete picture of where vacuum is being lost in HVAC system.

mj1pate

Ok, thanks.
then the vacuum solenoids all behave the same? I mean, I'm sure the solenoids controlling vent diaphragms are open or closed for vacuum. The heater valve solenoid requires varying levels of vacuum depending on requested temperature. Does the heater valve solenoid pulse fully opened and closed until the heater valve is positioned as per the requested temperature?

soontobered84

Yes, IIRC, all the solenoids are the same.

dr bob

The solenoids all operate with the same action. When energized, the solenoid connects the vacuum source to the actuated device port, and block flow through the vent port. When de-energized, the solenoid blocks flow through the vacuum source port, and allows flow between the vent port and the actuated-device port.

Vacuum from the system is sourced via a hose that connects the solenoid bank and a four-port cross-style rubber manifold piece. This part is located immediately to the right (passenger side on US cars) of the brake booster. Flow is through a small one-way check valve between the vacuum hose between an "eductor" or vacuum flow booster at the manifold, and the brake booster. The check-valve is connected via a tiny hose at the booster check-valve. The ports on the rubber cross connect to the source at the check valve, a hose that runs to the vacuum bottle in the rear of the left front fender, on S4+ cars the intake flappy solenoid valve, and the last to the HVAC solenoid manifold.

Diagnostic hints:

-- With the key off, you should be able to connect your MitiVac pump to the rubber manifold and draw a vacuum on all connected components. This can take a while as you will be drawing a lot of air out of the reservoir bottle in the fender.

-- With the key off, you should be able to draw and maintain vacuum from the hose to the rubber manifold by the brake booster to and including the solenoids. They are all closed, so you are pulling only the air from the hose itself and the rubber manifold that's directly connected to the solenoids. This is an easy test, as it only requires access to the end of the hose by the brake booster.

-- If that tests well and you are able to pull and maintain vacuum on the hose and the closed solenoids, your leaks are at the actuators.

-- If you fail that test, you can break the test down to sections by disconnecting the hose inside the car where it connects to the little rubber manifold for the solenoids, plugging the end there, and re-testing with your MitiVac under the hood. If that test fails, your connecting hose is leaking. If you pass, your distro manifold at the solenoids may be leaking, or you have a defective solenoid.

-- You will need to remove the little solenoid rack but leave the hoses connected for the next tests. You'll sequentially apply your MitiVac pump to the hose from each actuator, looking for those that don't hold. The hoses are color-coded, so refer to your WSM to ID the ones that don't hold and what they do.

-- You can cap the ports on the various valves that harbor leaking actuators to eliminate the effects of leaks on the rest of the system. Be aware that the deactivated/failed position of some of the actuators may not be what you want. Heater valve is open, defroster is open, center vent blend flap is at full-warm with restricted flow, etc. It's winter-survival mode effectively.

-- The heater valve is a binary on-off device. Coolant flow is not modulated for cabin temp control. Instead, the blend/mixing motor operates a blend door to adjust the proportions of air that has gone through the heater core area with air that has bypassed and gone through the AC evaporator. The decision protocol for fresh air flap and heater valve are governed by switch contacts in the blending motor and indirectly by cabin temp, outside air temp, and the temp slider position in the console controller.

Focus in fixing the vacuum system actuators before you try to get things to work partially, as the partial solution you achieve has only a small chance of being partial solution you desire.

Our regular vendors offer the rubber pieces alone for some of those actuators, and for others you'll find that you'll be just disconnecting the linkages to allow replacement of the rubber part only in the existing actuator housing.

The amount of disassembly required for access varies by actuator of course. Edsel Murphy's Second Law assigns probability of needing just an easy one at virtually zero, in my limited experience. Still, once in a while one gets lucky -- My latest vacuum system malfunction is caused by a failed vacuum diaphragm on the heater control valve itself. It's redemption after all the consoles and dashes I've had my hands in previously I guess. That valve is only 15 years old, by the way, a prophylactic "while I was in there replacing all the coolant hoses" replacement. New one is on the way I understand, so I knw what I'll be doing Friday afternoon when it gets here. Existing is tied closed with the plastic line capped. so 've had good AC all summer. Cold in the mornings now suggests heat would be a "good idea" though.

firemn131

Hey Michael,
I pasted a thread from when I began my HVAC dive..

Basically I reconditioned the solenoid valves with mineral oil. They now work as advertised..

Hope this helps.

John

https://rennlist.com/forums/928-foru...n-program.html