TheClairvoyant

I recently checked the 5 solenoids that control the vaccum pods for the hvac system.

Four of them were definitely bad. When checked individually with a Mityvac and a vacuum cap, some will hold vacuum at first, but the pressure drops like a rock when the ignition is turned on.

I ordered replacements and installed them. 2 hold pressure fine.

On 2 of them, the vacuum pressure will decrease on the Mityvac gauge with the ignition on, but the drop is very slow (from 15 to 10 inGH in 27.5 seconds)

My question - Is there an acceptable amount of pressure drop when testing?
With the engine running, I imagine vacuum is constantly being created, versus pumping up to test pressure with the Mityvac and not pumping anymore.

Is this very small pressure drop during testing something that wouldn't have an effect in the real world with the engine running, or is the solenoid bad?

With all the solenoids hooked into their respective lines, I tested at the main vaccum line in the engine bay. With the ignition switched on (engine not running) the Mityvac gauge dropped from 15 - 10 inHG in 44 seconds without any further pumping. Is this OK?

Before the replacements, this test showed a much quicker drop.

The good news is the vacuum pods themselves hold vacuum. No tearing any further into the console !!!

Alan

Not exactly clear how you are testing these - the final combined test seems to be the most obvious... you seem to have a leak somewhere - if its really only with ignition on its likely related to some solenoids opening. Which ones will depend on the flap & temp settings.

There will be a drop in mityvac test vacuum (then sustained) on the overall system when the ignition is turned on because some solenoids will open and that will drop vacuum in the rest of the system - due to the volume of the actuator diaphrams. The downstream actuator pod side of the solenoids always bleeds off vacuum whenever its not activated (e.g. its really a 3 way valve) - if it didn't the actuator pod would never go off - except for eventual leakage..

Alan



In practice you are probably OK with that leakdown since you probably won't be at WOT for that long and the rest of the time you wil be making vacuum. However the leak may get worse.

TheClairvoyant

Thanks for the reply.

I was testing each solenoid individually by disconnecting them from the vaccum lines and the rubber vacuum manifold. I would then connect one opening of the solenoid to the Mityvac and plug the other opening with a cap.

I would first test with ignition off. Vacuum would hold steady. With ignition on the vacuum would drop on the bad ones.

I was hoping to have the console buttoned up today and don't really want to wait for yet another replacement solenoid to replace the bad one the came. That said, it wouldn't make a lot of sense to go through the trouble of the repair and half *** it.

Alan

Again each solenoid actuator has 3 ports: inlet, outlet and vent.

When the solenoid is activated the inlet is connected only to the outlet.
When the solenoid is not activated the outlet is connected to the vent and the inlet is blocked.

If you test the outlet ports you will see major immediate leakage whenever the solenoid actuator not activated.

Alan

Mrmerlin

so what you want to do to test the pods (there are 5 of them) is to disconnect the hose for each pod from the manifold ,
NOTE you will be checking 3 of them under the console.
4th is the fresh air flap in the blower box look under the under the cowl panel for blue hose
5th is the HCValve white hose

then pull a vacuum if each pods holds vacuum reconnect its line and move on to the next line,

once all of the pods are checked and holding vacuum then you should have a leak free HVAC.

and also replace the heater control valve and short hose if they are over 10 years old.

Alan

So here are some helpers:

Heater Valve:
========
When the temp slider is full hot the heater valve will be open, solenoid off, no vacuum to actuator

When the temp slider is full cold with ignition on: the heater valve will be closed , solenoid on, vacuum to actuator.

Footwell Vent:
=========
Footwell vent (on in V & ^V flap modes with ignition on)

On - solenoid on = actuator getting vacuum

Defroster Vent:
=========
Defroster Vent (on in ^, ^V flap modes with ignition on)

On - solenoid off = no vacuum to actuator*

Recirculation Flap:
===========

In Recirc mode with ignition on: solenoid on, vacuum to actuator

Comb Flap:
=======
With temp slider full cold with ignition on, solenoid is on, vacuum to actuator

Try these different modes to see effects on your overall system's vac holding results.

Alan

* Note defroster flap is opposite sense to rest for failsafe vent position (e.g. vac failure - a vent needs to remain open).

TheClairvoyant

Thanks for the additional replies.

All of the pods have been checked themselves by hooking only each individual vacuum line to the Mityvac. They're all good.

I do have a new heater control valve and hose to replace as a precaution (not sure of the current valve/hose's age)

Thanks for the chart showing the different functions turned on/off by the HVAC sliders. I'll check more thoroughly with that today.

TheClairvoyant

After further testing using the pointers posted above, I definitely have one solenoid that's leaking slowly. It's one of the replacement one's just came recently. Oh well...

I'm using the leaking one for the defrost line for now and closed everything up, as I need to use the car over the next few days. When I get a replacement, at least I know which one is bad. Opening everything back up should go faster next time since it won't be new experience.

Mrmerlin

usually you dont touch the defrost pod as its always closed unless it been selected,
thus it has not seen much use so it doesnt usually leak

soontobered84

I am getting no heat whatever in the passenger cabin. I have tested all the lines and the actuators individually and all hold vacuum well. The heater valve is new. The HVAC vacuum manifold was removed and tested negative for leaks. I found that the number 2 solenoid (white vacuum line) to the heater valve leaked. The internal plunger was stuck between stations. My compadres were able to free the plunger with a quick shot of lithium. The solenoid now seems to function, and hold vacuum, but it seem to work in reverse from the other solenoids.

Is the solenoid for the white vacuum line different than the others? With the key off, my solenoid blocks vacuum from the heater valve, and with the key on, the vacuum prevents hot water from entering the heater core

FredR

John,

The heater valve defaults to the open position when the engine is shut off, thus vacuum is needed to close the valve if you are running the a/c. Not sure why it was designed this way- probably to keep the cabin as warm as possible while the owner is away from the car [in European winters]. Not good in a hot climate and why I removed my heater valve altogether. It is also possible to disconnect the arm and wire it in whatever position the owner wants.

We are currently having a cold snap- the temperature dropped to 14C last night!

Regards
Fred

StratfordShark

Check whether heater setting motor is running. Sit in car in quiet spot, ignition in run position. Move temp slider between full cold and hot positions. Do you hear motor run (it's above your right knee in footwell)?

If it's running, and you poke head in footwell, is the arm attached to the motor?

Alan

It defaults this way so that in predominantly cold climates (like Germany) if the vacuum or controller fails - you still get some heat and as noted it allows hot coolant to circulate through the heater core by convection when parked - does keep the cabin a bit warmer.

This is however quite counter-productive for very hot climates where keeping it closed when parked would be much better.

There are old threads on methods to do exactly that...

Alan

soontobered84

So, is my thinking correct that the solenoid for the heater valve operates differently from all the other solenoids and cannot be changed out with any of the other solenoids? Or am I just thinking crazy?

westija

They all have the same part number. The difference might be the way they are wired