Vacuum issue for heater temp - Ford Muscle Forums : Ford Muscle Cars Tech Forum
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post #1 of 20 (permalink) Old 03-02-2017, 06:13 PM Thread Starter
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Vacuum issue for heater temp

I've got no experience with vacuum so not sure if I've got dirty vacuum controls or actually failed parts. I'm hoping someone can give me some insight to understand how these parts work or fail.

My basic problem is I'm not getting any vacuum to the water control valve--the valve that opens to allow coolant from the engine to run through the heater hoses and into the heater core. Right now I'm running a vacuum line directly from the engine block to the WCV to get heat. I've worked my way backwards from the WCV and discovered that there is no vacuum at the temp control vacuum valve that connects the temp selector in the car to the WCV. I ran a vacuum line from the engine block to this vacuum temp controller and get no vacuum through the controller--vacuum to it but not out of it. I moved the temp selector in the car back and forth to see if it might be simply a dirty valve. No change. I worked backwards from there and discovered that there is no vacumm coming out through the firewall from the HVAC controller. I've got vacuum going into the HVAC controller--the vacuum doors for heat and defrost work as they should, but no vacuum coming out of the HVAC controller back through the firewall and on to the AC door controller or the above mentioned temp control. So clearly I've got a blocked vacuum line in the HVAC controller and a bad temp selector vacuum valve as well. I should mention that the vacuum motor that opens/closes the AC door does not work but of course it runs off this bad vacuum line so that may be way it isn't working.

So here's my question: I'm not hearing any vacuum leak at the HVAC controller. I'm clearly not getting vacuum back out through the firewall. Is it common for the HVAC controller to fail or simply get dirty and not function? What about for the temp control vacuum valve? If they're simply dirty would just shooting compressed air through them clear them out?
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post #2 of 20 (permalink) Old 03-02-2017, 08:31 PM
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Re: Vacuum issue for heater temp

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Originally Posted by bowdidge View Post
I've got no experience with vacuum so not sure if I've got dirty vacuum controls or actually failed parts. I'm hoping someone can give me some insight to understand how these parts work or fail.

My basic problem is I'm not getting any vacuum to the water control valve--the valve that opens to allow coolant from the engine to run through the heater hoses and into the heater core. Right now I'm running a vacuum line directly from the engine block to the WCV to get heat. I've worked my way backwards from the WCV and discovered that there is no vacuum at the temp control vacuum valve that connects the temp selector in the car to the WCV. I ran a vacuum line from the engine block to this vacuum temp controller and get no vacuum through the controller--vacuum to it but not out of it. I moved the temp selector in the car back and forth to see if it might be simply a dirty valve. No change. I worked backwards from there and discovered that there is no vacumm coming out through the firewall from the HVAC controller. I've got vacuum going into the HVAC controller--the vacuum doors for heat and defrost work as they should, but no vacuum coming out of the HVAC controller back through the firewall and on to the AC door controller or the above mentioned temp control. So clearly I've got a blocked vacuum line in the HVAC controller and a bad temp selector vacuum valve as well. I should mention that the vacuum motor that opens/closes the AC door does not work but of course it runs off this bad vacuum line so that may be way it isn't working.

So here's my question: I'm not hearing any vacuum leak at the HVAC controller. I'm clearly not getting vacuum back out through the firewall. Is it common for the HVAC controller to fail or simply get dirty and not function? What about for the temp control vacuum valve? If they're simply dirty would just shooting compressed air through them clear them out?
Hello,

I haven't seen the selector (dash control) fail, but the vacuum hoses under the dash and to the firewall bulkhead connector can become brittle or pulled off the nipples on the bulkhead connector. I'd check that first.

As a note I wouldn't put any pressurized air through the heater control thermostat (atop the blower housing in the engine bay), there are two delicate needle valves, seats and a rubber diaphragm. If you accidentally destroy the diaphragm or damage the needles/seats it will never work again. Less forgetting that part is not offered in aftermarket and you'll have to hunt a good used one (kind of rare) or an NOS one (expensive when they come on the market).

One more thought you might find interesting, here's a link I did a while ago on the HVAC system vacuum concerning heat mode. It's not as descriptive as I'd like, but it's a good start.

http://www.fordmuscleforums.com/gala...y-air-con.html

Hope that helps a bit.

Cheers.
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post #3 of 20 (permalink) Old 03-03-2017, 09:01 AM
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Re: Vacuum issue for heater temp

I don't think a vacuum leak at one of the underdash solenoids will cause the vacuum into the engine bay hose to fail. So I would say the issue is in the switch or the connector in the firewall or the hose between them. Here is a diagram of the hoses/cable and a pic of where the hose to the WCV (blue) comes out of the firewall (65 selectaire) Hope that helps.
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To every man upon this earth
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Putts drives a 1965 Galaxie. Rebuilt 390, 4100 on a Performer, MX, AC, PS, PB w Scarebird front discs on Cragar 17" S/S.
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post #4 of 20 (permalink) Old 03-03-2017, 08:58 PM Thread Starter
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Re: Vacuum issue for heater temp

Hey Desert, thanks for the helpful response. Do you think it is likely that the temp control valve is bad if I put vacuum to it off the engine and it still doesn't work?

I'll check the connections behind the dash again and see if I missed something. If there were a vacuum leak wouldn't I hear it or are the vacuum lines small enough that you wouldn't notice it?

Also do you know a supplier of the Ford color coded vacuum lines? The auto parts stores here in town don't have the color coded stuff.
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post #5 of 20 (permalink) Old 03-03-2017, 09:01 PM Thread Starter
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Re: Vacuum issue for heater temp

Thanks puttster for the response! Shooting compressed air through the connector in the firewall going to cause any damage? Is it common for this port to clog?
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post #6 of 20 (permalink) Old 03-03-2017, 09:38 PM
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Re: Vacuum issue for heater temp

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Originally Posted by bowdidge View Post
Hey Desert, thanks for the helpful response. Do you think it is likely that the temp control valve is bad if I put vacuum to it off the engine and it still doesn't work?

I'll check the connections behind the dash again and see if I missed something. If there were a vacuum leak wouldn't I hear it or are the vacuum lines small enough that you wouldn't notice it?

Also do you know a supplier of the Ford color coded vacuum lines? The auto parts stores here in town don't have the color coded stuff.
Hello bowdidge,

You're welcome. Well if you put engine vacuum directly to the temp control valve and you know you have at least 15" of engine vacuum as well as the dash heat controls set all the way on warm and there is still little to no vacuum at the water control valve, then I'd say there is a high probability the temp control valve is faulty.

As for hearing a tiny vacuum leak through the small hoses and orifice I doubt you would hear it with the noise from the engine. It doesn't take much of a leak in this system to lower vacuum because of the small hoses and fittings.

Do you have a vacuum hand pump? It is invaluable in this kind of diagnoses. They are cheap enough at places like Harbor Freight or even chain auto parts stores. One more note if the vacuum servo that closes the air con door (the servo in the engine compartment in line to the heater temperature control valve) has a ruptured diaphragm it'll bleed the vacuum off for the heater/temperature control valve rendering the system inop.

As for colour coded vacuum line, that's going to be a specialty item and I do not know where to source that from, probably hit the restoration places or Hemmings Motor News big catalog.

Hope that helps a bit.
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post #7 of 20 (permalink) Old 03-04-2017, 05:23 AM
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Re: Vacuum issue for heater temp

If the vacuum control switch to the engine bay is broken maybe you could put the engine bay hose on the defrost nipple at the switch. When you want heat, move the lever to defrost.

I painted my hoses but it is messy and if you have to buy the paint, a couple of bucks.

To every man upon this earth
Death cometh soon or late.

Putts drives a 1965 Galaxie. Rebuilt 390, 4100 on a Performer, MX, AC, PS, PB w Scarebird front discs on Cragar 17" S/S.
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post #8 of 20 (permalink) Old 03-07-2017, 02:35 PM Thread Starter
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Re: Vacuum issue for heater temp

Update. Got a vacuum pump and tested both the temp control and AC door vacuum motor. Both apparently are bad. I was able to get vacuum at the temp control valve but it would bleed off in about 20 seconds no matter the position ("on" or "off" and everything in between) with the "outbound port" (the one that leads to the water control valve) blocked or opened to atmosphere. I checked the vacuum motor for the AC door and I could get no vacuum at all. So both these are shot. I did check the vacuum hose connections from the HVAC controller in the car to the firewall and all the hoses were still soft and pliable with solid connections to the ports. With DesertXL's comment that a ruptured diaphragm in the AC vacuum motor would most likely bleed off any vacuum available I think I may have located the problem and will get to replace a few more parts.

I'll update with further progress as I locate and install the new parts.

On a side note I also installed a vacuum canister (had been running everything directly off the vacuum port on the intake manifold) but in one comment there was mention of a "check valve" between the vacuum manifold and the vacuum canister. I don't currently have this. Is it a necessity?
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post #9 of 20 (permalink) Old 03-07-2017, 06:33 PM
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Re: Vacuum issue for heater temp

With no check valve if you get a leak in the HVAC system it will act like a vacuum leak in the intake and the engine will run bad. Also, without a check valve the canister vacuum will rise and fall with acceleration, which is the same as just attaching the HVAC hose to the intake.

Your canister should have one built in. If not you can get one and put it on-line on the hose from the intake.

To every man upon this earth
Death cometh soon or late.

Putts drives a 1965 Galaxie. Rebuilt 390, 4100 on a Performer, MX, AC, PS, PB w Scarebird front discs on Cragar 17" S/S.
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post #10 of 20 (permalink) Old 03-07-2017, 07:27 PM Thread Starter
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Re: Vacuum issue for heater temp

Puttster, would the check valve be visible on the cannister? All I saw was two ports--one large and one small. I assumed the large port was for connection to the engine and the small was to connect to the HVAC. This was a NOS canister--the big black tin can type.
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post #11 of 20 (permalink) Old 03-08-2017, 09:16 AM
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Re: Vacuum issue for heater temp

If you got NOS, there should be a valve in there. You can test it though - a vacuum gauge on the small hose should stay steady when you gun the engine.

To every man upon this earth
Death cometh soon or late.

Putts drives a 1965 Galaxie. Rebuilt 390, 4100 on a Performer, MX, AC, PS, PB w Scarebird front discs on Cragar 17" S/S.
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post #12 of 20 (permalink) Old 03-20-2017, 04:26 PM Thread Starter
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Re: Vacuum issue for heater temp

Update: Got an AC door vacuum motor and temp control valve installed (about $40 for each part). Everything on the heater side is working now and finally have the ability control the heater temp from inside the car. Thanks for the help from everyone on tracking these problems down and providing answers to the questions.
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post #13 of 20 (permalink) Old 03-20-2017, 04:48 PM
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Re: Vacuum issue for heater temp

Bowdidge

Where did you get that AC door vacuum motor and temp control valve if you don't mind me asking? I think I may have the same or very similar problem(s) and may end up needing one or both of these parts (I will test though for sure).

1966 Galaxie 500 Fastback..Ivy Green, 352, AC
2007 Mustang GT 5-speed

Last edited by 66 Fastback; 03-20-2017 at 04:51 PM.
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post #14 of 20 (permalink) Old 03-21-2017, 04:15 AM Thread Starter
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Re: Vacuum issue for heater temp

Fastback,

I got the Vacuum Motor here: https://autoplicity.com/search?searchterms=MTC-YH161 Also available on Amazon. Amazon says it won't fit a Galaxie. That is wrong. It lists the LTD but not the Galaxie but for our purposes it is the same thing.

I got the Temp Control Valve Got on eBay. Search for C7AZ-18502-A. There are three listed right now, $45, $49, and $84.

Not sure that either of these will work with a 66 but they might.

Good luck!
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post #15 of 20 (permalink) Old 03-21-2017, 08:36 AM
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Re: Vacuum issue for heater temp

How you test your old temp control valve to see if it was working?

To every man upon this earth
Death cometh soon or late.

Putts drives a 1965 Galaxie. Rebuilt 390, 4100 on a Performer, MX, AC, PS, PB w Scarebird front discs on Cragar 17" S/S.
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