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  • September 26, 2022, 09:15:32 PM

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Author Topic: Always blowing hot air...unless AC is on  (Read 559 times)

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Offline Factory53

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Always blowing hot air...unless AC is on
« on: July 08, 2022, 01:37:08 PM »
Hi Everyone,

I've been meaning to post for a while but tried doing a bit of hunting around to see if my issue has been covered. I can't seem to find it having been discussed....and maybe its not an issue, it could be just the way it is.

My 84 Eagle Wagon will constantly release hot air from the vents once it is at operating temp. Even with the fan switch in off position and even with the temperature lever in the full left position (cold) position.

The only way to get the hot air to stop is to turn AC on and turn the fan on.

I've spoken with a few mechanics and they all seem to say the same thing "These old cars just do that!"....but I feel like that can't be the end of this.  :banghead:

I'm wondering if I've got some coolant lines hooked up wrong or something isn't working properly on heat/ac switches/console.

Has anyone else experienced this?

It won't be an issue in winter as I live in Canada and any extra heat is happily welcomed, but when its +35C (95F) air temp in the summer...its a bit much and my AC does work but its not super cold.

Any thoughts would be greatly appreciated.
1984 AMC Eagle Wagon Limited
1986 AMC Eagle Wagon (donor)

Offline Still Pat

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Re: Always blowing hot air...unless AC is on
« Reply #1 on: July 08, 2022, 01:43:55 PM »
I have the same problem (minus the A/C, mine MIGHT need recharged) in my wagon. I tried replacing the shut-off valve under the hood. It WAS stuck, but it didn't help.
'02 FORD E-150 Conversion van - Just sold!
'83 AMC Eagle wagon 258/auto.
'84 AMC Eagle sedan (4 door) 258/auto.
PREVIOUS AMCs:
'72 Gremlin X 304/3 speed
'81 Eagle Kammback 258/4 speed (Purchased new)
'82 Eagle wagon 258/5 speed Ordered new, traded Kammback)
'86 (I THINK) Eagle wagon - BlackBird 258/auto. (Got hit/totaled)
'83 Eagle wagon - White Eagle 258-auto. (Front subframe was rotted out - sold for parts)

Offline MIPS

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Re: Always blowing hot air...unless AC is on
« Reply #2 on: July 08, 2022, 03:23:38 PM »
Quote
I've spoken with a few mechanics and they all seem to say the same thing "These old cars just do that!"....but I feel like that can't be the end of this.  :banghead:
I've been told that too. I think it comes down to how well the foam seals in the air box are holding up.
I don't have AC at all so I have fresh air vents on both sides and controls under the steering column. Even though I pulled and refoamed my air box I still get a warm air draft with the blend control all the way in the blue, unless the other lever is set to OFF. There's no door on the inlet side of the heater core so you will always have air pressure forcing itself through the core and the blend door seals. The original foam I replaced was open-cell and the replacement foam was also open-cell so my bet is if you refoam the air box with high-temperature closed cell foam it would not be as bad.
If I want "cool" air I have to use the fresh air vents.

When it was 47 here last year it's no longer cool air. It's like sitting in a blast furnace.
« Last Edit: July 08, 2022, 03:30:48 PM by MIPS »

Offline Factory53

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Re: Always blowing hot air...unless AC is on
« Reply #3 on: July 08, 2022, 03:30:25 PM »
Thanks @mips and @stillpat. I'll have to take a look at the airbox and see if the foam is holding up.

There has to be a reason why so much hot air is coming through the vents even when the fan is totally off.

I'll keep digging around too, but thanks for the input you guys.

Cheers!
1984 AMC Eagle Wagon Limited
1986 AMC Eagle Wagon (donor)

Offline MIPS

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Re: Always blowing hot air...unless AC is on
« Reply #4 on: July 08, 2022, 03:39:57 PM »
I know that the AC equipped eagles have an extra vacuum valve on the HVAC controls that activates the heater core bypass when in the COLD position. Is it possible it's out of adjustment and should also be operating the valve in the COOL position? I've never seen the assembly myself but for economy sake that makes a lot more sense.
« Last Edit: July 08, 2022, 03:40:24 PM by MIPS »

Offline Factory53

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Re: Always blowing hot air...unless AC is on
« Reply #5 on: July 08, 2022, 04:13:24 PM »
I know that the AC equipped eagles have an extra vacuum valve on the HVAC controls that activates the heater core bypass when in the COLD position. Is it possible it's out of adjustment and should also be operating the valve in the COOL position? I've never seen the assembly myself but for economy sake that makes a lot more sense.

That makes total sense and I was trying to ask a couple mechanics if something like that might be causing it but I'm sure I was using the wrong terms.

Thanks again Mips, i'm going to the manual to see if I can chase something down!
1984 AMC Eagle Wagon Limited
1986 AMC Eagle Wagon (donor)

Offline Artmodels

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Re: Always blowing hot air...unless AC is on
« Reply #6 on: July 09, 2022, 12:47:09 AM »
I had EXACTLY the same problem when we bought our 83 wagon last week.  Previous owner stated ac does not work   I fixed that by hard vibrating/tapping on ac accumulator with ac compressor on and high revs to give lots of pressure in line.  This unblocked the acccumulator screen of accumulated sludgy oil buildup and it suddenly started blowing cold!

But......

 When ac was off, driving air pressure, or external wind over the hood would blow hot air out the vents, unless I closed the vent tab between the two center dash vents. At first I thought this would work, but of course the vent tab needs to be open to get any airflow. I noticed that the cold ac air had to cool this hot air down, so I wasn't getting full cold air benefit.

I took the dash center cover off, which is around the radio and two slider selector knob assembly(the one that lets you select between ac , heat, and vent, and hot/cold selector), and saw that there were two cables that fit onto pegs on the interior selector mechanism that rotates left to right.  The  one that attached onto the top right peg of the ac max/ac/heat/vent/bi level selector that opened and closed the vent door that allows outaide air to go the heater core had popped off of the peg, and was unattached, in the half open position.

I'll bet money that is what you guys have.  The cable end is curled into a round spring shape which pops down onto the 1/3" diameter , 1/2" tall peg on the rotating part, with no circlip or detent to prevent it from falling off eventually, under torque when you move the selector.

 I think that as the selector cable(which is almost identical to a bicycle brake cable) gets stiffer/gummy with age, and the ac selector which most likely used to slide easily when car was new, now needs considerable force to push the gummed up cable through the now resisting sheath, thus putting torque force enough to pop off the cable off of the peg acutator.

My idea for a fix, was to spray wd40 into cable/sheath end and work back and forth until it moved smoothly and easily, then put the loop end of the cable back onto the peg.

Voila, now when you move it from heat to ac setting, hot air immediately stops, and actually zero air movement comes in the center vents from the outside air moving through the heater core to the vents.  Then when ac fan is turned on, and ac kicked in, boy, the air froze my fingers, after only a few seconds!

Hope this description helps you guys fix the issue!
« Last Edit: July 09, 2022, 12:57:40 AM by Artmodels »

Offline MIPS

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Re: Always blowing hot air...unless AC is on
« Reply #7 on: July 19, 2022, 12:57:11 AM »
Dug into a salvaged AC package to see how the switch works and here you can see the lever underneath where on COOL rests against the white vacuum switch that operates the heater core bypass valve and a pair of adjustment screws. When you switch to COLD you push the button in and the valve operates.



Also yes, the foam on the blend door had broken down in a way that meant that even if the core is blocked off you will still get leaks through the core. It's a lump of closed cell foam.

« Last Edit: July 19, 2022, 01:24:11 AM by MIPS »

Offline Factory53

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Re: Always blowing hot air...unless AC is on
« Reply #8 on: July 27, 2022, 05:36:51 PM »
This is great information...I'll see if I can get brave enough to take the cover off and see what is happening under there.

Awesome find Artmodels!

I had EXACTLY the same problem when we bought our 83 wagon last week.  Previous owner stated ac does not work   I fixed that by hard vibrating/tapping on ac accumulator with ac compressor on and high revs to give lots of pressure in line.  This unblocked the acccumulator screen of accumulated sludgy oil buildup and it suddenly started blowing cold!

But......

 When ac was off, driving air pressure, or external wind over the hood would blow hot air out the vents, unless I closed the vent tab between the two center dash vents. At first I thought this would work, but of course the vent tab needs to be open to get any airflow. I noticed that the cold ac air had to cool this hot air down, so I wasn't getting full cold air benefit.

I took the dash center cover off, which is around the radio and two slider selector knob assembly(the one that lets you select between ac , heat, and vent, and hot/cold selector), and saw that there were two cables that fit onto pegs on the interior selector mechanism that rotates left to right.  The  one that attached onto the top right peg of the ac max/ac/heat/vent/bi level selector that opened and closed the vent door that allows outaide air to go the heater core had popped off of the peg, and was unattached, in the half open position.

I'll bet money that is what you guys have.  The cable end is curled into a round spring shape which pops down onto the 1/3" diameter , 1/2" tall peg on the rotating part, with no circlip or detent to prevent it from falling off eventually, under torque when you move the selector.

 I think that as the selector cable(which is almost identical to a bicycle brake cable) gets stiffer/gummy with age, and the ac selector which most likely used to slide easily when car was new, now needs considerable force to push the gummed up cable through the now resisting sheath, thus putting torque force enough to pop off the cable off of the peg acutator.

My idea for a fix, was to spray wd40 into cable/sheath end and work back and forth until it moved smoothly and easily, then put the loop end of the cable back onto the peg.

Voila, now when you move it from heat to ac setting, hot air immediately stops, and actually zero air movement comes in the center vents from the outside air moving through the heater core to the vents.  Then when ac fan is turned on, and ac kicked in, boy, the air froze my fingers, after only a few seconds!

Hope this description helps you guys fix the issue!
1984 AMC Eagle Wagon Limited
1986 AMC Eagle Wagon (donor)

Offline Factory53

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Re: Always blowing hot air...unless AC is on
« Reply #9 on: July 27, 2022, 05:38:52 PM »
Wow...do you know if anyone has ever replaced the foam? I'm assuming it can be done by finding a block of closed cell foam and shaping it to fit.

Thanks so much MIPS!

Dug into a salvaged AC package to see how the switch works and here you can see the lever underneath where on COOL rests against the white vacuum switch that operates the heater core bypass valve and a pair of adjustment screws. When you switch to COLD you push the button in and the valve operates.



Also yes, the foam on the blend door had broken down in a way that meant that even if the core is blocked off you will still get leaks through the core. It's a lump of closed cell foam.


1984 AMC Eagle Wagon Limited
1986 AMC Eagle Wagon (donor)

Offline MIPS

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Re: Always blowing hot air...unless AC is on
« Reply #10 on: July 27, 2022, 08:18:30 PM »
I had access to 1/4 and 1/2" sheets of white foam which I trimmed to fit and used Super 77 to stick it to the old surfaces.
Two things here:

1 - Super 77 does not handle prolonged high temperatures and will start to detach. Use proper upholstry adhesives.
2 - I used open-cell foam because it was easier to work with and fold over but it lets air pass through it, which is a bad idea in an air box.

Offline Factory53

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Re: Always blowing hot air...unless AC is on
« Reply #11 on: September 08, 2022, 06:18:31 PM »
I had access to 1/4 and 1/2" sheets of white foam which I trimmed to fit and used Super 77 to stick it to the old surfaces.
Two things here:

1 - Super 77 does not handle prolonged high temperatures and will start to detach. Use proper upholstry adhesives.
2 - I used open-cell foam because it was easier to work with and fold over but it lets air pass through it, which is a bad idea in an air box.

Again, awesome information. It looks like Kennedy American website lists a heater core with new foam for sale still...I'm thinking I may go that route. Living in Canada I'll be pumping hot air through there 8 months of the year!

Thanks for the information!
1984 AMC Eagle Wagon Limited
1986 AMC Eagle Wagon (donor)

Offline AMC of Houston

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Re: Always blowing hot air...unless AC is on
« Reply #12 on: September 08, 2022, 11:06:11 PM »
Aircraft-grade silicone foam works great for this sort of application.  Impervious to high heat.  I have an ex-Audi-engineer buddy that turned me on to it -- uses this to re-foam Porsche heater boxes (newer Caymans and Boxsters have a problem with rotting foam).  He also has a business designing and manufacturing A/C systems for small aircraft, so he knows his stuff!
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