I'll make this as short as possible, posting on an iPhone. 1987 FC, cold air blows through all vents but a soon as I switch it over to heat, the air stops, as if something is suddenly blocking the vents. A/c as well as air works but heat doesn't. I thought blower motor but then wouldn't that cause it to never blow? So is there a vacuum line connected to that switch that switches vents over that came disconnected or what? Any help tracing the problem would be appreciated. Let me know if you need more info and ill hop back on the pc, was hard enough typing all this out. Thanks.

 

The heat section of your climate control has two main components.

First, there is a water control valve that allows hot water to flow through the heater core.
This ain't your problem because it's failure wouldn't stop air from flowing, you'd just get cold air.

Second, there are flapper doors (motor operated) that direct air through the heater core, or not.
This is probably where things are wonky.

The Training Manual shows how to test/troubleshoot the system but of course, they want you to use a Logicon tester...which I'd guess you haven't access to.
The easiest first step (comparatively speaking) would be to swap in another Logicon and see what happened.
You may get lucky.

If not, the next step would be to remove the dash and inspect the main heater box to see if all the flappers/motors are working properly.
If you end up going this far, make sure to inspect the heater core because now would be the time to replace it if necessary.

Has the climate control worked correctly in the past or are you just now finding out?

 

Now that i think about it, i don't think it ever worked. I just went to use it one day and that happened, but i don't recall ever testing it when i bought the car. When i switch it to heat i can hear a motor somewhere switch over so that makes me think it's not the logicon but the flaps themselves, maybe some linkage came disconnected or something. Is there any way to get to them without tearing apart the whole dash? It's my daily driver so I'd like to be able to just get in there and fix it before the weather starts getting too cold.

 

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/rigging-air-mix-motor-lever-get-heat-back-979713/

 

feel the heater hose inlet and outlets at the firewall, if there is a restriction in the core then the passenger side will be much cooler than the inlet on the driver side.

 

True, dat...but it wouldn't shut down his airflow through the ducts.

 

ah right, i admit i was lazy and didn't read the original post.

 

I almost replied to check the simple things first like installing a new thermostat

 

I have a spare logicon if should feel so inclined to buy another one to test with is does still fully work and nothings broken or missing

 

removing the dash is not a huge chore. shouldnt take more than an hour (probably 30mins if you are a speedster and have all the tools ready)if you can find a write up to follow so you dont go in blind and muck up the order.

 

you dont have to remove the dash to check the logicon

 

I feel i should mention, as well as airflow being restricted while in heat, defrost doesn't blow either. It switches through all of them, but on defrost/feet and full defrost, it always blows fully on the feet. So maybe that is affected the same way as the heat is? Every mode works fine except heat and defrost, those don't blow air at all. I'll go look in the faq's thread for a how to on testing the logicon (if there is one) before i go out and buy a new one, don't have a whole lot of cash to be throwing around.

[edit]

So i read up, and apparently the symptoms for the logicon and the air mix motor are almost the same. So according to my specific problems, which is it more likely to be? Any ideas? Seems like both are a pain in the *** to replace, but i should still be able to do what satch posted no matter what, right?

 

I've been thinking...If the air-mix motor was bad, and it wasn't opening the vent to allow the hot air to flow through, then wouldn't air still come through the vents? It would just never get cold, right? So that's not the problem then, and i wouldn't be able to just reach under and manually move that vent to get hot air, like satch posted. Which leads me to what, the logicon? Is it possible for only one setting as well as the heat to fail but have everything else working fine? And if so, can i just tear it apart and resolder it like various websites have mentioned, replacing resisters and such if any are bad? There's gotta be something short of dropping almost $300 on a new one, i can't afford that at all...And it's supposed to start getting really goddamn cold these next few weeks, too

 

Here is what the vent control flaps do during the various modes:


As you can see, depending on the mode desired, more than one flap door is involved.

I'm more familiar with the FD system (which is completely different) and since my heat has always worked, I've not studied the FC system, but it might be possible that when in heat/defrost mode, one or two flaps are fighting each other and just sealing the airflow totally from the ducts.

Painful as it may seem, I think pulling the dash and checking the main heater box is your best bet. At the very least, you should be able to set the flaps to the correct position for heat and bypass the Logicon for the winter.