Heater issues

[Russellrh72]

Hello all! I have a heat issue that has me stumped. I rebuilt the heater box before install and rebuilt the heater control valve.... original brass style valve. I do in fact have heat but it seems to only work, or work as it should I would say, when the fan is off. If the fan is off with the floor vents open and I'm driving down the road, I can feel the slightly greater than trickle of heat into the floor board and it is pretty hot. Feels great! When I turn the fan on that burst of heat disappears in a couple of seconds and is replaced with warm-ish air that almost feels blended. I don't feel like it has been that way the entire time since I replaced the heater box to be honest.

 

Before I realized that it might be a problem only when the fan came on, I replaced the thermostat and water pump. Did not fix the problem. In fact it might have slightly cooled off the air coming in when the fan is off as well. Before that it would almost burn my ankles. I read in my searches that some heater ills have been cured by burping the coolant system, but it doesn't seem like that would be the case here since I do feel good heat coming in when the fan is off. If really does feel like blended air. Could the fan be installed wrong? Wouldn't that cause no air to be blowing into the cabin? There is a noticeable push of air into the cabin when I turn the fan speeds on.

 

The car has always run cool. The needle would rest at about 4 o'clock before the thermostat change earlier this week. Now it rests just out of the blue which seems really cool to me. But again, I do feel good heat coming in when the fan is off and I'm driving down the road. Any help would be appreciated. Thanks in advance!

 

Rob

[jgerock]

Hi Rob-

Assumed by your username you have a 72.  This year will have the larger heater valve and core.  Depending on the temperature lever position, you should feel a rush of air out the bottom vents while driving.  When the fan is turned on, does air blow out of the vents?  If not, then your fan motor could be wired backwards.

 

You might also have to adjust the cables to fully open/close the flaps on the heater box.

 

Jim

[Russellrh72]

Ahhh Jim you raise an interesting point. I have a '71, but I installed a box from a later car. It was the first one I found here in the FAQ in decent shape. I took the sliders off of the box and retrofitted early cables to match the panels in my car. The entire system had been deleted from my car by a previous owner. Long story short I bought the box before I was aware of the differences in the cables and sliders and such. 

 

To answer your question, if I put the temperature on hot, and open the vents to the floor, but leave the fan off, I feel hot air "walking" into the cabin at the floor. If I turn the fan on (low or high since my car has the two speed pull knob on the dash below the head light switch) the air starts to "run" into the cabin, but the temperature of the air gets noticeably cooler. Still has some warmth to it but like I said it feels like it has mixed with some cold air or something. I almost get more benefit in terms of heating by leaving the fan off and having the hot air just filter in slowly with the vents open. 

[Themis]

My incomplete list to troubleshoot:

1. Make sure both hoses to the core are hot (from engine firewall) after the engine has reached operating temperature, to confirm valve is opening and core is free

2. Easy to check (again, from firewall) that fan is pushing air in

3. Confirm vents are opening/closing properly. For bottom vents, can check with flashlight; for top vents, all air should be diverted to top.

 

Assuming all of these are OK, I suspect seal between box and core, or core not seated properly. There should be a piece of foam making that seal. I guess that if the seal is not there, low pressure air (as in car driving, fan off) might get warm and pass through the core, but high pressure with the fan on will go around the core (just a guess)

Edited January 28, 2023 by Themis

[Mike Self]

Didja accidentally reverse the wires to the blower motor?  Being a DC motor, it's happy to run in either direction; running backwards will not help airflow into the car, but will do wonders for sucking odors, cigarette smoke etc out...

 

Second thought.  The lever that controls the temperature actually has two cables (this is true on early and late heater boxes).  One cable goes to the water valve, while the other goes to an "air mixer door".  It's located below the heater core, and allows air to pass directly into the heater box without going through the core, thus improving air flow when the weather is warm and the heater is merely serving as an air intake.

 

With the temp control all the way to cold, the mixer door is wide open; as you move the temp lever towards hot, that second cable gradually closes the mixer door until all the incoming air must pass through the heater core.  If the mixer door control is incorrectly connected, or not connected at all, you'll get plenty of air even without the blower motor, but it won't be very warm, even with the temp control set to full hot.  

 

mike

[Russellrh72]

@Mike Self.....this seems like a possibility. When testing that, by having the slider all the way to heat (which should close the fresh air flap), the floor vents open, and the blower off, I don't feel the cool air like I do when the fan comes on. Could it be that the fan simply makes the cold air from the fresh air flap more noticeable? I think not, as the air without the fan is noticeably warmer than it is when the fan is on. With the fan on I can actually feel really cold patches of air when I put my hand down to my feet and then other spots where it feels warmer. Some of the patches almost feel as cold as air would coming in through a cracked window....and it's in the 30's here after dark. But the overall mix still ends up being warmer than that of course, which is why I use the word blended. The cabin gets to a survivable temperature after running it for quite some time. Maybe there is in fact something not sealed of flush as @Themis suggested. I will investigate the fresh air flap some more tomorrow. Thanks for all the ideas....let me know if you have anything else I should consider! 

[PhilC]

This fresh air mixer flap could well be an issue on mine as I have symptoms that this could cause. @Mike Self is it easily accessible and how?

@Russellrh72 when you investigate this could you take some pictures please.

[jgerock]

11 hours ago, Themis said:

My incomplete list to troubleshoot:

1. Make sure both hoses to the core are hot (from engine firewall) after the engine has reached operating temperature, to confirm valve is opening and core is free

2. Easy to check (again, from firewall) that fan is pushing air in

3. Confirm vents are opening/closing properly. For bottom vents, can check with flashlight; for top vents, all air should be diverted to top.

 

Assuming all of these are OK, I suspect seal between box and core, or core not seated properly. There should be a piece of foam making that seal. I guess that if the seal is not there, low pressure air (as in car driving, fan off) might get warm and pass through the core, but high pressure with the fan on will go around the core (just a guess)

+1 on this response.  Perhaps the foam has deteriorated at the core edges.

Also make sure the arrow on the valve points toward the cabin and the operating lever is attached to the valve correctly.

[Mike Self]

8 hours ago, PhilC said:

This fresh air mixer flap could well be an issue on mine as I have symptoms that this could cause. @Mike Self is it easily accessible and how?

Unfortunately it's not accessible--or hardy visible--with the heater assembled and installed.  I once tried to replace that two wire cable control (hot water valve & mixer door) by cutting a hole in the heater box with my trusty Dremel tool.  I was able to remove the broken cable, but couldn't force the new cable end over its peg--the fit was too tight, and the angle all wrong.  

 

You might catch enough of a glimpse of the mixer door in action by shining a flashlight up one of the footwell heater outlets (pax side is the easiest to contort yourself into) and look for motion while moving the appropriate lever.  Or if you have  little inspection camera...cut a hole in the heater box and poke the camera through the hole...You can glue the cut out piece back on, or use a little piece of scrap aluminum or plastic sheet to cover the hole.

 

mike

[PhilC]

26 minutes ago, Mike Self said:

Unfortunately it's not accessible--or hardy visible--with the heater assembled and installed.  I once tried to replace that two wire cable control (hot water valve & mixer door) by cutting a hole in the heater box with my trusty Dremel tool.  I was able to remove the broken cable, but couldn't force the new cable end over its peg--the fit was too tight, and the angle all wrong.  

 

You might catch enough of a glimpse of the mixer door in action by shining a flashlight up one of the footwell heater outlets (pax side is the easiest to contort yourself into) and look for motion while moving the appropriate lever.  Or if you have  little inspection camera...cut a hole in the heater box and poke the camera through the hole...You can glue the cut out piece back on, or use a little piece of scrap aluminum or plastic sheet to cover the hole.

 

mike

Thanks Mike, I’ll try the contortion method first. If I can see movement I’ll assume it is working 🙂

[Russellrh72]

Just an update on the heater issue....I contacted the supplier from whom I purchased the thermostat and they sent me a 71 rather than the 80 I requested. So that hopefully explains some if not all of this. Just going through a check list....

 

-My heater valve is opening and closing properly it would seem

-The hoses at the fire wall could be hotter....hopefully the thermostat will improve

-Both floor vents are opening and closing as should. 

-fan is pushing air

 

@PhilC.....in regard to the fresh air flap, you CAN get a glimpse of the door with the box installed. I got on the passenger floor board with a flash light in my right hand, and used my left hand to slide the heater control on the dash back and forth. The brand new foam that I installed on the flaps during the rebuild probably helped its visibility because the flashlight picked up the shine of the material, but I could see it opening and closing. There is always a possibility that when closing it doesn't get all the way flush, but seeing it go back and forth was enough evidence for me to feel comfortable with it. Especially since I checked them all before install and don't remember anything that would cause concern. 

 

So I am going to install another thermostat with the higher temp rating and see what that does. I'm hoping that the lower rated thermostat was enough to give me hot air when the fan is off and not pushing it, but just not hot enough to keep up with all that air being forced. Sound possible? We'll see....

[Son of Marty]

When you refilled the radiator after your work did you have the nose of the car elevated with the heater on hot, you may have a bit of air lock going on there.

[Russellrh72]

@Son of Marty....this was something else I was considering. I did not do that when I installed the thermostat and water pump a couple of weeks ago but saw it mentioned in one of my searches when looking into the issues. I will do that when I install the higher temp rated thermostat for sure. Is what you mentioned above all there is to that process? Elevate the nose, turn car on, heater valve open? 

 

 

[Son of Marty]

Usually that's all it takes, you need to get the top of the radiator at or above the heater core then warm the car up with out the radiator cap on should get the air out.

[Themis]

Make sure heater valve is open when you refill the radiator. In my experience, if there is a bubble trapped in the heater core, you will see a difference in the temperature between the two heater hoses going through the firewall (with the heater valve open):  The ingoing one will be very hot, but the outgoing will be cooler