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Discussion Starter · #1 ·
Hello all,

Seemed like a good time of the year to share what I did to overhaul the heater portion of the Ford HVAC system. Maybe it can help someone else out with little or no heat.

So no doubt, those with factory air con systems have come across a problem with the HVAC system as a whole, either little to no heat or no air con.

The system on these is a little odd in that it was overly complicated for what it did and still doesn't allow for dehumidified warm air to the windscreen (defrost).

These systems unlike the heat only option do not have a mechanical blend door, instead the temperature of the heater core and evaporator itself is modulated to your hot-cold setting.

To start, you have to have a good source of vacuum. The engine needs to at least have 15" of vacuum to fully open the heater coolant valve. Stock engines should have no problem with this.

Given the small diameter of the hoses it only takes a small leak and the whole system can be affected.

I found vacuum leaks on my reservoir can itself, especially at the top.


The best way I found was to thoroughly clean it (carb spray works just fine too) to wash grease and muck off it. Then using a small vacuum hand pump apply a small vacuum and allow the leak to gently pull in the sealant (RTV) but no to hard to where the leak reappears.

The next thing to check for is a check valve in the supply. Some say it's in the top part of the vacuum reservoir while some literature shows a separate valve inline to the reservoir. I probed around on this one and there was no evidence of anything in the top port, no spring or disc. Either it was never there or it disintegrated.


If your tank doesn't have a check valve in it or it doesn't seal well. I found this one at Napa.



Once that the vacuum reservoir and supply are checked out and working properly, next to check the remainder of the system.

Old hoses turn hard and leak and if yours are questionable I'd replace them. I know there's a lot under the dash and in the engine bay.

The next place to check is the heater coolant/control valve itself. Usually the ancient seal will start to leak or it will corrode to the point it will no longer move, or the diaphragm will rupture/tear/crack/leak.



This one wouldn't budge. Problem is these are not reproduced exactly to fit. There are generic ones that will work.



But the original mounting bracket take a little modification to hold the new part. I need to mention there are two flavors of heater valves. One that is normally open and one that is normally closed. Our gals need the one that's normally closed, which is the uncommon one.

Here's the modification I did to the bracket to hold the newer valve.








For the retaining screw, I ground it to a dull point at the end which dimples the valve behind the plunger, but since the plunger has a small travel this does not interfere with it and so it seals tight with no vacuum and it's very open when vacuum is applied.

Next is checking the heater vacuum thermostat.



With the thermostat set to the cold position there should be a vacuum leak (vacuum bleed off) if checking from the heater valve control port. If checking from the vacuum supply side it should hold vacuum when set to full cold.



Next set the thermostat to full heat and plug the port to the heater control valve and pull vacuum on the supply port. It should hold vacuum.

If it doesn't hold vacuum especially in the last test, the thermostat is dirty or has a ruptured diaphragm. It can be taken apart, but there are two small needle and seats (valves) in there. The needle is the size of a hemming needle. It's almost analogous to working on a wrist watch as far as delicacy is concerned.

I had pictures of taking this apart, cleaning and inspecting and reassembling. I lost those pics. But I still have 3 more of these Ford HVAC systems to R&R so hopefully in the future I can cover this better.

If you're confident in taking it apart go for it, if not, occasionally I see these NOS on EBay for 100-250 dollars. Something to keep in mind.

Lastly you want to make sure the Bowden cable that connects from the dash 'hot-cold' selector is adjusted properly to the cooling and heating thermostats under that plastic cover in the engine bay.



Another quick check to make sure you have enough vacuum at the heating thermostat is to check the vacuum servo motor here in the picture on the right. With the engine running in the heat or defrost positions it should have pulled in its arm hard. If it's not pulled in or not pulled in all the way and fully seated then you need to recheck the vacuum lines and the HVAC selector on the dash for vacuum leaks.

And please it kind of goes without saying to check that the heater core itself isn't full of scale or plugged or the 90' heater hose elbow on top of the engine isn't plugged as well.

Hope that helps solve heat problems.

Cheers..
 

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I'm in the process of getting the parts for the comfort stream ventilation, have it all except 1 piece of duct work. Back in the day I swapped bodies on another 67 for a driver and added the factory AC. I can attest to the overly complicated system. BTW yours looks like it would rival the factory off the assembly line new look.
 

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Discussion Starter · #3 ·
I'm in the process of getting the parts for the comfort stream ventilation, have it all except 1 piece of duct work. Back in the day I swapped bodies on another 67 for a driver and added the factory AC. I can attest to the overly complicated system. BTW yours looks like it would rival the factory off the assembly line new look.
Hi 5851a,

Is that the nomenclature for the rear window vent in the package tray? If you have a picture of it or the parts I would love to see it. I like learning about all the little esoteric options on these cars.

Cheers
 

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Desert,
Thanks for the write up. I also had to use one of those heater valves that is "almost" the same as the one that came on our cars. It was enough to get the heat going for the winter. I still have some other things on the system that I need to check out.

My heater vacuum thermostat had a ruptured diaphragm. I ended up finding a replacement on eBay. Not sure if the replacement is working right. Bought me a mighty vac I can use to check it out no since I know what it's supposed to do.
 

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There is just a mention of it under the LTD stuff. On the 2 drs it consists of the air vents in the dash like a AC car and uses the blower motor and under hood parts of a regular heater car. There are vents on the inside of the doors at the rear bottom and the exhaust flaps at the rear edge of the door in the door jamb area. They also have a water shut off valve and vacuum tank. Ducts connect the dash vents to the under dash heater defroster plenum. It's kind of neat, just like newer stuff when you flip it to vent.
Ford Muscle Cars of 1967
 

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You guys are brave. I messed around with dusty, crusty factory HVAC. everything seemed to be shot I my compressor and condensor were both MIA. I ended up replacing it with a new Nostalgic AC system. It reuses the factory slider controls unlike some of the others.
 

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Thanks a lot for taking the time to document and post this, DesertXL. Do you have the factory part number as well as a source and part number for your aftermarket heater control valve?
 

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Discussion Starter · #8 ·
Thanks a lot for taking the time to document and post this, DesertXL. Do you have the factory part number as well as a source and part number for your aftermarket heater control valve?
Hello TerryVeiga,

My pleasure to help someone out. As far as a factory part number I do not have one off hand. You could reference the Ford Interchange Manual or the Illustrated Parts Manual and you should get a part number. I posted links to uploads for these a while back, they're on the forum here.

If you still cannot find the part number I still have two old 66 gals with the original control valve probably still in them, I'd have to unbolt them and read the P/N... but it's cold out and I'm going to whinge about it :)

For the aftermarket replacement, the part number is 74604, I bought these Partsmaster brand from Rock Auto a while back for 12 dollars each. I had a look they have Four Seasons brand (same part number) for 18.48. You should be able to order them locally at Autozone, Oreillys, Napa, etc. But don't be surprised if they are 30-50 dollars at that point.

Cheers..
 

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I always wondered what that heater vacuum thermostat was named and what it looked like under there. Now I know. Would it be fair to say that if it is busted/leaking then hot water cannot flow to the heater core, because the water control valve is normally closed?


Good info.
 

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Discussion Starter · #10 ·
Hi puttster,

Yuppers you are right, any loss in vacuum from the engine to the control valve and little to no coolant will flow through the heater core even on full heat.

Cheers.
 

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I fought that system in my 65 country squire for years trying to get it to put out enough heat,never could find a good heat/a/c vacumn motor that is on the firewall so I wired it to heat but still was not all that great. About 2 years before I sold it I found the vacumn can on the fender well was shot and after replacing it I had great heat and defrost. Since I robbed all the good parts from all the 65 to 68s in the local old junkyard I doubt I would ever buy one with factory a/c again,I like the just heat systems better and have a dealer installed a/c system to use if I want to cool off on my next one.
 

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Is there any chance you could re-post the pictures since photobucket has gone off-line for freemium users? I'm going through the same thing now, and I can't seem to figure out what the temperature control system needs to look like. On my '66 the factory A/C was completely disconnected by a previous owner, but all of the components still seem to be in place (except maybe the hot water valve).
Thanks!
 

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Discussion Starter · #14 ·
Is there any chance you could re-post the pictures since photobucket has gone off-line for freemium users? I'm going through the same thing now, and I can't seem to figure out what the temperature control system needs to look like. On my '66 the factory A/C was completely disconnected by a previous owner, but all of the components still seem to be in place (except maybe the hot water valve).
Thanks!
Hello bishop,

I'll try to repost the pictures. It'll take a while to find them, load them to my website and redo the thread here. Just as a note 3rd gen Ford full size ('65-'68) all have similar HVAC systems, there's little esoteric differences like on your '66 the coolant valve to the heater core is mounted on the outer wing/fender lip where as a '68 is mounted to the inner apron. You get the idea.

Cheers
 

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Discussion Starter · #15 ·
Hello all ,

Since I cannot edit the old original post, I'll repost it here with the pictures linked from my website instead of photobucket. Seemed like a good time of the year to share what I did to overhaul the heater portion of the Ford HVAC system. Maybe it can help someone else out with little or no heat.

So no doubt, those with factory air con systems have come across a problem with the HVAC system as a whole, either little to no heat or no air con.

The system on these is a little odd in that it was overly complicated for what it did and still doesn't allow for dehumidified warm air to the windscreen (defrost).

These systems unlike the heat only option do not have a mechanical blend door, instead the temperature of the heater core and evaporator itself is modulated to your hot-cold setting.

To start, you have to have a good source of vacuum. The engine needs to at least have 15" of vacuum to fully open the heater coolant valve. Stock engines should have no problem with this. Given the small diameter of the hoses it only takes a small leak and the whole system can be affected.



I found vacuum leaks on my reservoir can itself, especially at the top.

The best way I found was to thoroughly clean it (carb spray works just fine too) to wash grease and muck off it. Then using a small vacuum hand pump apply a small vacuum and allow the leak to gently pull in the sealant (RTV) but no to hard to where the leak reappears.

The next thing to check for is a check valve in the supply. Some say it's in the top part of the vacuum reservoir while some literature shows a separate valve inline to the reservoir. I probed around on this one and there was no evidence of anything in the top port, no spring or disc. Either it was never there or it disintegrated.



If your tank doesn't have a check valve in it or it doesn't seal well. I found this one at Napa.



Once that the vacuum reservoir and supply are checked out and working properly, next to check the remainder of the system.

Old hoses turn hard and leak and if yours are questionable I'd replace them. I know there's a lot under the dash and in the engine bay.

The next place to check is the heater coolant/control valve itself. Usually the ancient seal will start to leak or it will corrode to the point it will no longer move, or the diaphragm will rupture/tear/crack/leak.



This one wouldn't budge. Problem is these are not reproduced exactly to fit. There are generic ones that will work.



But the original mounting bracket takes a little modification to hold the new part. I need to mention there are two flavors of heater valves. One that is normally open and one that is normally closed. Our gals need the one that's normally closed, which is the uncommon one.

Here's the modification I did to the bracket to hold the newer valve.











For the retaining screw, I ground it to a dull point at the end which dimples the valve behind the plunger, but since the plunger has a small travel this does not interfere with it and so it seals tight with no vacuum and it's very open when vacuum is applied.

Next is checking the heater vacuum thermostat.



With the thermostat set to the cold position there should be a vacuum leak (vacuum bleed off) if checking from the heater valve control port. If checking from the vacuum supply side it should hold vacuum when set to full cold.




Next set the thermostat to full heat and plug the port to the heater control valve and pull vacuum on the supply port. It should hold vacuum.

If it doesn't hold vacuum especially in the last test, the thermostat is dirty or has a ruptured diaphragm. It can be taken apart, but there are two small needle and seats (valves) in there. The needle is the size of a hemming needle. It's almost analogous to working on a wrist watch as far as delicacy is concerned.

I had pictures of taking this apart, cleaning and inspecting and reassembling. I lost those pics. But I still have 3 more of these Ford HVAC systems to R&R so hopefully in the future I can cover this better.

If you're confident in taking it apart go for it, if not, occasionally I see these NOS on EBay for 100-250 dollars. Something to keep in mind.

Lastly you want to make sure the Bowden cable that connects from the dash 'hot-cold' selector is adjusted properly to the cooling and heating thermostats under that plastic cover in the engine bay.



Another quick check to make sure you have enough vacuum at the heating thermostat is to check the vacuum servo motor here in the picture on the right. With the engine running in the heat or defrost positions it should have pulled in its arm hard. If it's not pulled in or not pulled in all the way and fully seated then you need to recheck the vacuum lines and the HVAC selector on the dash for vacuum leaks.

And please it kind of goes without saying to check that the heater core itself isn't full of scale or plugged or the 90' heater hose elbow on top of the engine isn't plugged as well.

Hope that helps solve heat problems.

Cheers..
 

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What a thoughtful re-post. Just in time for winter, too. Thanks XL.
 

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Thanks so much! The heater vacuum thermostat pictures are exactly what I was looking for. Mine is pretty clearly shot - I'll have to keep an eye out for a NOS unit.
 

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I have some NOS heater/ a/c parts that I might sell,I will try to avoid one with factory air if I buy another 65 so I will probably never use them.
 

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THIS is an AWESOME thread!! I so needed this !
Thanks!
 
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