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Discussion Starter #1
85 supra p type. Been through most of the heater threads and a couple of other heater writeups on other sites.

Blower works all speeds.
Water valve on firewall bypassed (plumbed around by P.O.)
Heater core has good coolant flow.
No heat.

If I let the engine idle in place, I'll get lukewarm air. Not real warm, but slightly warmer than ambient. As soon as I start driving it cools off to ambient.

Pulled the dash and radio. disconnected the gold colored vacuum solenoid from the linkage behind the radio so the linkage can be moved by hand. No matter where I set the linkage, the air temp doesn't change.

1. This is the warm/cold adjustment damper, yes?
2. WTF am I doing wrong?
 

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vacuum solenoid???? so if u move the temperature control, do u hear a click? do u see that linkage moving?
 

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Discussion Starter #4
Have you changed the coolant any time lately? If so, did you "Burp" it?
I've not opened the cooling system until today. Just bought it a couple weeks ago. 2k miles on a fresh short block, so it's been drained/filled recently. According to the PO the heat worked last spring, but he used the car as a sunny day driver only.

vacuum solenoid???? so if u move the temperature control, do u hear a click? do u see that linkage moving?
Linkage doesn't move, but I've got MANY capped/removed vacuum lines under the hood. Engine runs fine, but many of the vacuum lines to auxillary components have been removed. That's why I removed the linkage from the vacuum solenoid - so I can manually move the linkage to try to "force" the heater to work.
 

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so even if u move that linkage the heat doesnt come out from the vents? is that right? maybe is air trapped on the heater or the heater could be clogged.
 

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Discussion Starter #6
Yes - moving the linkage doesn't change heater air temp.

heater core isn't clogged - disconnected hoses and ran water through the core. Good flow. Is there a trick to getting air out of the core?
 

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Umm...maybe I am wrong but I think the "Water valve on firewall bypassed (plumbed around by P.O.)" would make the temperature selector lever irrelevant any way, that valve is what you are opening more to get "hot", or closing more to get "cold". Did the new short block have a thermostat in it?? I will bet you don't have one...here is the statement that leads me to that "If I let the engine idle in place, I'll get lukewarm air. Not real warm, but slightly warmer than ambient. As soon as I start driving it cools off to ambient. The fan is doing it's job... reducing the temp of the coolant, you should be glad of this one. Probably the PO had problems with the heat system prior (bypassing the control valve would be evidence of that) and he/she took it (the thermostat) out. Where does the temperature gauge needle go to when the engine is "hot" ?? if your answer is either "it never moves" or "I think it is broken because it is always low" or "where is the temperature gauge". My suggestion is to replace the thermostat (that is if there is one there (other wise you will be putting one into the vehicle where it belongs). To get hot air out of the vents in the mean time (and to test my theory) place a piece of cardboard in front of the radiator to block off air flow, the amount of hot air should be directly related to how much air you have stopped from going through the radiator, more air blocked off = more heat. I would start with about 33% coverage. This story is very familiar as this is what I went through for a winter until I joined this forum and determined that was my problem. It is a very easy job to do, just be careful putting the housing back on use permatex ultra grey (imo you don't need a gasket) and remember the bolts are there to hold it in place not position it correctly...in other words don't tighten them too much...even if it leaks the first time. If it leaks, take it back off, clean it up and when you put it back on, just use more permatex grey and kind of rotate it slightly {both ways CW and CC about 10 to 15 degrees} to get a good seal on the permatex) when you put it on. Hope that helps.
 

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Discussion Starter #10
Umm...maybe I am wrong but I think the "Water valve on firewall bypassed (plumbed around by P.O.)" would make the temperature selector lever irrelevant any way, that valve is what you are opening more to get "hot", or closing more to get "cold". Did the new short block have a thermostat in it?? I will bet you don't have one...here is the statement that leads me to that "If I let the engine idle in place, I'll get lukewarm air. Not real warm, but slightly warmer than ambient. As soon as I start driving it cools off to ambient. The fan is doing it's job... reducing the temp of the coolant, you should be glad of this one. Probably the PO had problems with the heat system prior (bypassing the control valve would be evidence of that) and he/she took it (the thermostat) out. Where does the temperature gauge needle go to when the engine is "hot" ?? if your answer is either "it never moves" or "I think it is broken because it is always low" or "where is the temperature gauge". My suggestion is to replace the thermostat (that is if there is one there (other wise you will be putting one into the vehicle where it belongs). To get hot air out of the vents in the mean time (and to test my theory) place a piece of cardboard in front of the radiator to block off air flow, the amount of hot air should be directly related to how much air you have stopped from going through the radiator, more air blocked off = more heat. I would start with about 33% coverage. This story is very familiar as this is what I went through for a winter until I joined this forum and determined that was my problem. It is a very easy job to do, just be careful putting the housing back on use permatex ultra grey (imo you don't need a gasket) and remember the bolts are there to hold it in place not position it correctly...in other words don't tighten them too much...even if it leaks the first time. If it leaks, take it back off, clean it up and when you put it back on, just use more permatex grey and kind of rotate it slightly {both ways CW and CC about 10 to 15 degrees} to get a good seal on the permatex) when you put it on. Hope that helps.
Thermostat is fine. Car will warm up to operating temp in a few minutes of idling or a couple miles of driving. Temp needle moves up to about 11:30 position (12:00 being dead center of gauge) and will stay in that general area regardless of engine/vehicle speed.

My understanding is that the coolant valve on the engine bay firewall is an on/off valve, not a modulating valve. It simply allows/denies flow to the heater core. The air damper/linkage/solenoid behind the radio modulates air flow across the core, regulating temperature. (Correct me if I'm wrong please) In that case, a bypassed coolant valve means the heater core should be hot all the time. Not good in the summer but it was 38*F here last night so I'm ready for some heat.

White bread is KC Kansas City??
KC is Kansas City. Home of great barbeque and horrible sports teams.
 

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Discussion Starter #11
what about when u move the linkage can u hear the door inside the heater case moving?
The linkage rotates with a little resistance, so I think damper inside is moving, but I haven't verified 100% by pulling the ductwork out. Right now I've got the entire lower dash out but I'm trying to avoid having to pull the rest unless I have to.
 

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I've got the same problem on two of my cars..one 85 and one 84. The one 85 I was only driving in summer so it didn't really matter but I have to resolve the issue for both cars....as my "Winter" Supra was T-boned (Rest in piece)

Apparently, the is a connector/(sensor??) by the passenger side headlight motor that has to be connected (& apparently has a pink wire). There is also a sensor inside the center console (with the armrest) that compares inside temp to outside.

I still have to methodically go through all the possible options (including "burping" any air bubbles in the system.

Besides the write up here somewhere on the site, I've been told the first two point by someone who knows Supras inside out & backwards.

To the original OP, let's both let the other know how we make out.

Cheers,
 

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Discussion Starter #13
Found the problem - at least part of it.

The rod running from the back side of the vacuum solenoid linkage up to the damper in the duct was sliding in its plastic retaining clip. Moving the linkage at the solenoid wasn't actually moving the damper even though it appeared to. I repaired the clip, moved the linkage over to hot, and pinned the linkage in place for now. So at least I've rigged heat for now.

My vacuum solenoid still isn't moving on its own, so I can't reinstall the linkage and use the dash warm/cold control. I've pulled the cabin air sensor to force the electrical side to call for heat with no results, so I think the problem is vacuum related. Especially since the vacuum system on this car has been hacked and plugged in several places. In either case, it's a problem for another day. It was a nice warm ride to work this morning, which is good enough for now.

Thanks for all the replies.
 

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SWEET!

I hope my problem is the same as yours. Can you take a picture of your solution? I'm having a problem visualizing what you did to solve the problem.

Thanks!
 

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Discussion Starter #15
Already reassembled everything so no pictures this time.

Just pull the lower passenger dash, glovebox, heater controls faceplate, and radio. You'll be able to get to everything you need.
 

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I am glad you have heat and I certainly do not want to get into a fight about this....
but I would like to ask where did you get your understanding from? Remember, I'm not trying to put you down or anything, I just want to know how credible the source is and if the firewall valve is simply an on/off valve why are there two electrical connections to it?

"My understanding is that the coolant valve on the engine bay firewall is an on/off valve, not a modulating valve. It simply allows/denies flow to the heater core. The air damper/linkage/solenoid behind the radio modulates air flow across the core, regulating temperature. (Correct me if I'm wrong please)"

Because I can not confirm or deny this statement, I would like to ask if it is true, how does this damper do this? by opening and closing? WHAT IS CONTROLING THAT?

How do you explain the part about heating up to luke warm if sitting still and dropping back to ambient if driving? How is this accomplished? what is the damper doing to cause this?

Also if the heater core is constantly hot, from bypassing the valve, and the fan works shouldn't you be able to manually set it to push out hot air where you want it? Which seems to be the goal right now.


I really want to help - do not take this as an attack - I know what you are going through
I have been there!!
 

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Discussion Starter #17 (Edited)
Where to start.....in order I guess.

My understanding comes from two places. 1. from reading literally every heater thread on this site. In several of those threads, long standing members with much more knowledge of these cars than I have comment that the valve on the firewall is an on/off valve. The idea is that if heat is called for before the car is up to operating temp, the valve stays closed to warm the block faster. The heater core isn't allowed to flow until the motor is within normal operating temp range, as dictated by the engine bay temp sensor. That sensor is the second electrical connection, though I can't visually confirm this because my firewall valve was unplugged and bypassed by the PO and the electrical connections are missing. 2. From visual inspection of the valve. I'm an industrial electrician, and though automotive electrical is different than industrial, it's not completely foreign. The valve shape doesn't appear to be a modulating valve design, but rather a snap open solenoid valve that only has two positions - open and closed. I could be wrong, but continue reading and you'll see why I still think that's correct.

FYI several of the heater threads on this site reference an outside link that had a very good troubleshooting list and a decent explanation of how each part functions. I don't have the direct link in front of me, but if you search for "heater" in thread titles it's mentioned several places.


Behind the radio under the dash is a vacuum actuated solenoid. It's actuates a linkage, which moves the damper rod, which causes the damper in the duct to move from warm to cool. The solenoid is a spring return to cold setup, so with no vacuum it is held in the cool position. The more vacuum that's applied to the solenoid, the farther to warm it moves.


I think the reason I was getting lukewarm air at idle was I was pulling warm engine bay air in through the blower. The cabin air intake is on the same side as the header/exhaust, and at idle my engine bay is very warm due to the unwrapped header. Also when I said I got lukewarm air, it was far from hot. It was about 75 degrees outside and I was getting maybe 90 degree air out of the vent. As soon as the car starts moving it dropped back to ambient.

The heater core was constantly hot - my damper wasn't moving due to an unhooked connecting rod, so I wasn't drawing air across the core. The temp slider on the dash is electrical (potentiometer or rheostat - I haven't investigated far enough to determine). All the electrical components of the heat system must work to get warm air via the dash controls because there is no mechanical connection to the damper until you get back to the vacuum solenoid under the dash. This means that the temp slider, cabin air temp sensor under the console, the vacuum switching valve, the vacuum solenoid, the on/off heater valve on the firewall, and the engine bay temp sensor must all be working to get heat the normal way.

I don't have the a/c compressor installed and don't plan to reinstall it, so I don't need cold air any time soon. I've also got a baby due any day, so I didn't want to spend hours troubleshooting all the electrical. My blower works fine, so I just repaired the damper rod and moved the newly reconnected linkage at the vacuum solenoid over to hot. That immediately got hot air flowing out the vents. I pinned it in place so it can't move. Now I've got good hot air blowing, and this setup will work fine until I get around to further troubleshooting down the road.

I am glad you have heat and I certainly do not want to get into a fight about this....
but I would like to ask where did you get your understanding from? Remember, I'm not trying to put you down or anything, I just want to know how credible the source is and if the firewall valve is simply an on/off valve why are there two electrical connections to it?

"My understanding is that the coolant valve on the engine bay firewall is an on/off valve, not a modulating valve. It simply allows/denies flow to the heater core. The air damper/linkage/solenoid behind the radio modulates air flow across the core, regulating temperature. (Correct me if I'm wrong please)"

Because I can not confirm or deny this statement, I would like to ask if it is true, how does this damper do this? by opening and closing? WHAT IS CONTROLING THAT?

How do you explain the part about heating up to luke warm if sitting still and dropping back to ambient if driving? How is this accomplished? what is the damper doing to cause this?

Also if the heater core is constantly hot, from bypassing the valve, and the fan works shouldn't you be able to manually set it to push out hot air where you want it? Which seems to be the goal right now.


I really want to help - do not take this as an attack - I know what you are going through
I have been there!!
 

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vacuum lines reversed

I had this problem too, took me awhile to figure out the two vacuum lines were reversed on the firewall valve and to compound the problem, I also had a linkage slip. I finally learned thru trial and error. When I first bought the car - in the beginning - either I had too much heat in summer or no heat at all in fall/spring - don't drive 'er in winter. My trips to the dealership, which cost lots and resolved nothing (got sucked in to unnecessary repairs). Since then (10 years) I won't go to a dealership unless I absolutely have to... have learned lots about these cars.
 

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Thanks, that was certainly more than I expected. Again, I am glad you have heat and good luck with the baby comming soon. Perhaps I will see you around town. I have a blue 84 P-type so if you see that going by you honk and wave!! Send me a PM if you want to look at the vac lines (or what ever) on a vehicle for reference. Sometimes that helps more than the reference books.
 
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