Heat on all the time. Logicon?
 

Just got the new project - 86 n/a.

Blower motor controls work fine, lights in the logicon all work, air control valves must be working fine as the air can be moved to the different locations, but the heat stays on at all times. Temp control slide has no effect at all on the air temp. A/c is not hooked up, but at least I ought to get outside air temps, right, instead of heat?

I would assume, from reading the threads that this is probably a logicon problem?

Thanks, in advance, for your replies.

Mark

Could be, but my 88 SE did exactly the same thing when I bought it. Turned out to be the ignition switch. What happens is that one of the contacts in the switch is marginal, and if I very carefully turned the key towards the "off" position with the car running, I heard a faint click behind the dashboard as a relay kicked in, and then the Logicon worked properly. Curiously, that contact in the switch also controlled the sunroof, so that also didn't work until I jiggled the key. Give it a try.

any ones else had this problem and sloved it other than nopistons, cause ive had the same problem since ive owned my s5, and i dont think its my ignition switch-no problems with sunroof

Yeah, there is a motor that controls the fresh air vent, yours is probably stuck open and your getting all the engine heat. Look under your dash on the drivers side right behind the radio there should be a little mechanism there you can manually open and close it like I do mine.

Heat & AC service manual
 

I have no FSM section for the S4 HVAC, but the S5 manual has it.

Check your "temperature control actuator"

click here do download the .pdf file

onepyramid,

nopistons makes an interesting point that makes me remember that the mystery heater problem I experienced didn't go away until after I had my ig switch replaced because it was worn out (at about 110K miles).

Prior to that, I had fixed some annoying traits in my environmental controls by replacing my logicon. But if my memory serves me correctly the heat problem just seemed to go away after the ig switch replacement.

Good luck with the problem.

That's way off base. The fan is fed either fresh air vent from the cowl in front of the windscreen or recirculated air from the cabin. It cannot get air from the engine bay.

Air temperature is controlled by a valve that regulates coolant flow through the heater core. Either this valve is stuck open or the Logicon is not sending a signal to it.

Check down there anyway, when my blower is off I can still feel hot air blowing on my feet so I reach down with my right hand and pull down a piece of wire that I have connected to a lever that opens and closes a vent down there. The previous owner rigged it so it would stay open, I figgured this out because my feet were boiling last summer and I read something that lead me to inspect that area and I found the rigging and decided to see what the lever did and thats when I heard that "flump" sound like when you switch from fresh to recirculate. No more hot feet, thats my point.

I THOUGHT that I completed the dreaded logicon repair ritual. Pulled the center console, removed the stereo(upgrading that anyway), removed the logicon PCB, and resoldered almost every solder connection. Put it back in and voila-nothing! Same old problem; good fan control, decent AC, no vent controls and no heat. Oh well, now I guess I need to check the mechanicals for the vents and the heat exchange stuff. Grrrrrrrr. My ignition switch was changed out when my RX was recovered/repaired from an auto theft attempt('nother story) but my sunroof works fine so I guess it shouldn't be an ignition switch problem. When the vent controls stick do the control motors tend to burn out? (say it ain't so)

how much does a logicon cost?

check out icemark at www.mazdamark.com