SQLGuy

Hi folks,

Finally got a bit of time to work on the car today. Since so many people had had problems with them the stock ones, I had ordered a Four Seasons heater valve to replace my plastic one. Unfortunately, Rock Auto sent the half-metal (and more expensive) one rather than the all-metal one shown in the catalog picture.

Anyway, I first checked whether the original valve was being closed by vacuum... the arm was pulling in when the car was started with A/C on, so I figured the valve was leaking. I pulled the old one, manually closed it, and blew through it: a tiny bit of leaking in the backflow direction, none in the proper flow direction, and the valve looked good... nonetheless, since I had the new one anyway, I installed it.

Checking the new one, I see that, while the arm is moving, it doesn't seem to be getting enough vacuum to close really tightly. What's the next place to look to see why theres' vacuum here but not a strong enough vacuum to get the job done?

BTW, previous checks revealed that the footwell door is closing, but that the comb in the center of the dash may not be acting correctly.

Thanks,
Paul

WallyP

It is common for the HVAC vacuum actuator diaphragms to fail.

If you go to our web site, click on the photos to enter, then the tips & links on the left, then Wally's World, then HVAC, you can download a paper tht describes the system and tells how to test the vacuum actuators.

Let us know if we can help.

dr bob

Paul--

Reinforcing Wally's info some, the line to the HVAC vacuum system is purposely small, mostly so that an HVAC vacuum leak won't affect other vacuum systems. Limiting airflow through that system also means that actuators won't slam open or closed. The affected systems would be flappy on S4+ cars, cruise control on earlier cars with vacuum CC actuator, and the vacuum lock actuators on the even earlier cars. The net effect of having the restricted vacuum line is that even a small leak in one of the actuators reduces vacuum available to the other actuators.

For summertime use, I add a small wire-tie to hold the heater valve closed at all times. The solenoid that actuates the heater valve goes to relaxed position whenever the key is shut off, so even though the heater valve is tight when closed and all the rest of your vacuum system is OK, the valve will go open when the engine is off. So you dash to the grocery store. In there five minutes searching for the coldest beer, then back out to head home. During that five minutes, convection has caused the hot water from the block to migrate up into the heater core. On engine start, the solenoid is actuated immediately and the valve goes closed again, but you get a facefull of superheated air until the AC ia able to move some of that heat back outside. A simple wire tie through the hole in the valve frame and around the little lever arm will solve the problem for you all summer. When you are ready for heat again next fall, just snip the tie and you are back in business. This is a less-than-ten-minute fix for those playing along at home. The lower air cleaner housing comes off for access to the valve. Do it on a cold engine though; don't burn your fingers!

SQLGuy

Hi Wally,

Well in the meantime, figuring that the HVAC vacuum manifold should be my next stop, I searched and found John Pirtle's writeup. Pulled the manifold, checked the orange line, and sure enough, there's a leak there. Guess a new actuator is in order.

In the meantime I've plugged the comb flap connection to the manifold with a screw, and the heater valve is now closing tightly.

Cheers,
Paul

SQLGuy

By the way, I found some discussions regarding 3rd party diaphragms for these actuators, and also the possibility of using some Mercedes ones. Anyone have any experience with this, or recommendations on sources?

Thanks,
Paul

dr bob

Roger has at least one of the sizes done in a better silicone material. I'd start there. If doing the comb flap actuator, the footwell actuator is easy and accessible at the same time.

Mrmerlin

Roger has the new diaphragm instead of buying the whole part just swap out the diaphragm

NoVector

You meant "opening" correctly, right? When it's closed, it's not recycling the air. I thought Dwayne's sight (and Wallys) were excellent--but Dwayne having pictures helped. http://www.dwaynesgarage.norcal928.org/

Good luck! / Bruce

SQLGuy

Since I have the vacuum manifold accessible, which waiting for a replacement comb filter actuator or bladder, I decided to check why I was STILL getting heat through the vents with the AC off but the system set to full cold. I found that vacuum is only applied to the heater valve when the AC is switched on. Is this correct/expected?

Mrmerlin

your going to have to fix all of the leaks in your diaphrams first before you start testing the system,
I would say that once the pods are are all leak free the rest of the system will work as it should as well the cruise control .
With the system off , the hot water valve should be closed but you need vacuum to hold it in this position.
Part of the reason i am saying this is so you dont try to fix something thats not broken.
just fix the pots then test

SQLGuy

I've already checked all the vacuum circuits for leaks. The only one that leaks is the orange (comb filter), and I have it blocked off.

Cruise control works perfectly, BTW. IIRC, it's electric servo in the S4's and later, and vacuum in the S3's and earlier.

I was mistaken in my previous post, though. I was looking at the wrong line. The heater valve is getting vacuum when the temp slider is set towards the cold end of the spectrum, and not getting it when set more towards the warm side (with the AC off). There's a bit of delay in the transistion, though. I'll need to drive a bit with it set full cold with AC off to see whether I'm still getting heat when set to full cold. If so, I'll probably put the original heater valve back in.

Paul

Mrmerlin

try setting the temp slider to cold and turn on the AC see if the HCV stays closed if not then the setting motor has a fouled transistor

SQLGuy

I tried an experiment this morning. It was nice and cool, and since the car had been sitting, undriven, for more than 24 hours, the heater core was cool as well.

I set the temp slider all the way to 65 degrees, left the A/C off, turned the blower on a bit, and drove to work. The air remained cool throughout the drive as the car warmed up.

This tells me a couple of things:

1. The heater valve is remaining closed when it should be
2. I'm not drawing hot air from the engine compartment into the blower
3. When shut down, and warm, the air plenum is REALLY heat soaking from the heater core

Number 3 makes me think that either having the heater control valve default to open is a significant design flaw or the disintegrated foam on my mixer flaps is a bigger problem than I had thought. (or both)

I have adjusted the mixer flap arms, but the DS one is at the limit of its adjustment now and I'm not sure the gap is entirely closed. Should I be looking to replace that foam?

Has anyone done or considered a conversion to normally closed for the HCV? Anyone know of a suitably-sized HCV that opens with vacuum? Converting the logic on the vacuum switch that operates it would be a fairly simple task with a PNP transistor and a resistor, but I'd rather have a NC heater valve than try to reverse the spring and actuator of a NO one.

Thanks,
Paul

EDIT-------------------------------------------------------------------

After a bit of Googling, I found a few discussions about this that took place here last year, in 2007, and in 2003. Sounds like the most elegant solution propesed there was to add a vacuum solenoid in-line with the white vacuum line, to keep vacuum from bleeding off of the HCV when ignition is shut off. I may do that, but I'd still like a NC HCV, since that makes for a somewhat simpler solution.

Thanks,
Paul

dr bob

Paul--

I've ID'd a NC valve (Ford Fiesta) and considered adding it in series with the existing valve. Plumbed to intake vacuum, it would only open when the engine is running. There's also an option to add another solenoid to the vacuum side of the existing valve, and tie the valve to the 15 circuit so vacuum system is active to the HCV only when the ignition is on. So many mods, so many places to leak, it's much safer/easier for me to just add the cable tie in the early summer, remove it at the beginning of winter here.

The failed positions of the various actuators is intentional. Worst case is a cold rainy day somewhere near where the cars are built. In that case the heater vave is open, the defroster flap is open, and you get hot air on the windscreen so you can see. worst case in summer is either window open or AC running so you don't get baked.


On replacing the comb flap actuator: The footwell flap actautor is inches from the comb flap actuator, and is the easiest of the two to replace. It's a good WYAIT effort. Adds less than ten minutes to an afternoon project.

The defrost and recirc flap actuators are at opposite ends of the dash area. The defrost flap is on the WYAIT list when the dash is out for something else. Recirc flap replacement is part of a blower and evaporator cleaning project that will dramatically improve your AC performance.

SQLGuy

Hi Bob,

In CA, I can see wanting to just force shut off heat for the summer. In Colorado Springs we've been known to have snow, here in the city, in every month except August. We had snow last year, at my office, on September 2nd.

Likewise, in Germany really hot summer days aren't that common, we get a lot more heat and a lot more sunshine here.

In general, I think the factory had good ideas about how they intended things to work. I'm not sure I agree with this one, though. Does that Ford Fiesta valve use the same hose diameters?

Thanks,
Paul