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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..
I know this is an old post but I thought I would see. I don’t have a check valve and there is just a vacuum line hose coming from the vacuum canister going to nowhere. I know the other smaller line is going where it needs to but I have no idea where the large one is supposed to connect on the engine. If anyone could post a pic or two of the way yours is set up that would be greatly appreciated. And the car does have factory ac as well.
 

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The larger hose hooks to the engine.
Where does it hook onto the engine? my engine was rebuilt at some point by one of the previous owners and they did not hook this stuff back up. They didn't want to deal with it is my guess, so I have no previous reference as to where that larger hose goes.
 

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Where does it hook onto the engine? my engine was rebuilt at some point by one of the previous owners and they did not hook this stuff back up. They didn't want to deal with it is my guess, so I have no previous reference as to where that larger hose goes.
Here are some pictures. (sorry about the terrible lighting)
167321
167322
167323
167324
 

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There is a brass connector behind the carb where it should go,from the pics it looks like there is a rubber plug where that hose should go.
 

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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..
I do not need any a/c, mainly because none of the lines are hooked up and i really just don't have the money to have that converted to modern stuff. Can I just bypass the heater control valve, and have the heater hose go straight through to the heater core? Or will that damage something? And if i cant do that, can I just bypass the vacuum for the heater vacuum thermostat and have it go straight to the heater control valve?
 

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Discussion Starter · #29 ·
I do not need any a/c, mainly because none of the lines are hooked up and i really just don't have the money to have that converted to modern stuff. Can I just bypass the heater control valve, and have the heater hose go straight through to the heater core? Or will that damage something? And if i cant do that, can I just bypass the vacuum for the heater vacuum thermostat and have it go straight to the heater control valve?
Hello IceCole15,

There's no reason why you can't run the coolant full through the heater core (same as on a gal 500 with heat only from the factory), you're not going to hurt anything. The drawback is the blower motor speed is the only control you'll have of heat and it will be hot all the time coming out of the defrost or floor register.

Cheers
 

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I have the control valve bypassed on my 65 Montclair since it leaks but you will need the vacumn line hooked up so all the heater functions will work,if there is no vacumn all the air will come out the a/c ducts and will not have any heat and no defrost.
 

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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.what

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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