Interior heating issue
 

I searched around, but I was not able to find and solid answers, so I come asking for help!

93 Canadian touring auto to manual swap is the main jist. AC pump, condenser and lines are not installed. The evap core is still in the HVAC box. I had the dash off, HVAC box out and apart to replace the foam on the actuator doors as it was falling apart. After assembling it, I was able to test the mode and blend door actuators when they were installed on the heater box. Both moved freely and had zero issues after assembly. Currently, with the key on, I can move the temperature and mode dials and hear the actuators move, air comes from the corresponding vents as it should.

My main issue is the lack of heat when indicated coolant temps are over ~70°C, interior temps do not seem to matter (i'm not sure if there is a interior temp sensor for feedback on the HVAC board). From first start, cold I can select any range on the warm side of the temperature dial and it is blown through the vents (aside from the front facing ones - warm air in the face). As soon as coolant temps climb over 70°, every temperature and vent selection blows straight outside air. Feeling the lines going to / from the heater core after a drive seem alright, they are as warm as any other coolant line. Another thing I noticed - if I park and shut down with the blower fan on and begin to drive before the coolant temp has dropped, as soon as I being to move (above a crawl but under 5km/hr) I can hear the blend door actuator move.

Any ideas?

First thing is just making sure the blend door is moving when it's commanded to move with the blue-to-red temp selector dial.

I don't believe there's a thermostat or anything fancy in the heater system, if the blend door is positioned to blow air over the heater core you get hot air.

The outlet vents need to be set on "floor" instead of "face" - the FD's heat is designed to only go to the floor vents. I think you can get some warm air out of the face vents but there you go.

It's possible (and very common) that the heater core is plugged up internally which will reduce the effectiveness and amount of heat. Back flushing the heater core and using some sort of radiator flush type chemical in it can help out.

At the end of the day the FD's heater, for whatever reason, just doesn't work that great. You would think with a motor that puts out thermonuclear levels of heat that you'd have an amazing heater but no. Sad part is the FC's heater was amazing, even high mileage and not well maintained FC's had heaters that would run you out of the car in short order. And they would heat face or feet vents too.

Dale

Are you sure about that? My heater core is a nuclear reactor. Even with the new foam on the flappers it still seems to leak ambient heat into the AC vents enough to reduce the effectiveness of my AC.

Of course, it doesn't help that its 110 outside either I guess.

Maybe it only gets really hot when you don't want it to.

Mode and blend doors are working properly. The blend door can be heard adjusting with every notch in the selector, and a full sweep when turning the knob quick enough. This morning I was able to get amazingly warm heat, to the point I had to turn it down to half temperature on the dial. After turning it down it fed only outside temperature air and would not return to blowing warm air, not even moderately warm air.

I used some radiator tubing, a $10 aquarium pond pump (harbor freight), a five gallon bucket and some CLR to try and clean out my heater core. It didnt' work 100% but it did get slightly better. I filled the buck with CLR diluted with DI water, submersed the pump and plumbed it to one side of the heater core by the firewall. It discharged back into the 5 gallon water and cycled like that for 2-3 days. I would switch the inlet and outlet every couple hours. It might help to have a lid on the bucket too as the CLR builds a tower of bubbles from being agitated.

Your blend door actuator might be flaking out if it puts out good heat sometimes and not others. https://www.rx7club.com/3rd-generati...ators-1066668/

This sounds exactly like what is happening to mine. I'm thinking that below a certain temp it will work properly, but once heated will default to full cold for some reason. Today after work with the car in the sun the whole day, heating the interior, I tried to cycle the blend door and it did not respond. Thanks for the tip!

The weather warmed up and I put the heating issue to the side for a bit. When I pulled apart the actuator today, nothing seemed amiss - the motor spun in both directions with direct power applied, cleaned the sweepers and their traces, fluxed and re-flowed all solder joints to a less than stellar result. The diodes and capacitor tested fine. Plugged in and not being touched, the actuator doesn't work, plugged in and applying decent force to the female side of the connector (on the actuator) allows it to work fine. As soon as I let go, the actuator returned to the cold side of the throw. I have a feeling that there is a break on a trace of the sensing side of the actuator.

Hmmm... did you re-flow solder on the connector pins too? Might just need to buy another used one and refurb that.

Turns out the pin had failed inside the connector on the actuator itself, there was zero continuity from the tip of the pin to the board. I soldered a jumper wire to an unused pin, re-pinned the harness connector and added a note on a tag if I (or anyone) has to work on it in the future. Almost 2 weeks later and I have rock solid heat control.
https://cimg6.ibsrv.net/gimg/www.rx7...3bfb0f2031.jpg

Wow, good find on that! Wonder if that's a weird thing that happened to just your car or if it's more common?

Dale

Bringing back this thread because I'm stumped.

My car has never had working heat since I got it a couple years back so I figured I would address it now that I have moved to a colder climate. I'm having an issue where the heater barely works, like if it is blowing full blast at the coldest setting with the a/c off, it is noticeably cooler than with the heater on, but that being said the air blows not even lukewarm with the heater on full blast. This is very noticeable when it is 10-20F outside which it is sometimes.

First I fixed the heat dial which was loose, then I check to make sure that the actuator is working properly, which it is. I visually inspected it and it all turns and does so the appropriate amount depending on how much the switch is turned.
Then I flushed the heater core using radiator flush and hot water and had full flow. I did this for a couple hours and then cleaned everything up and tried letting the car warm and check the heat at full blast in the footwells and still nothing. At first there was some warmth but its almost like it cooled off from just a few seconds of the fan blowing. I double checked the actuator and it still works and at least seems to be turning the mixer door.

The only thing I could think of is that even though the actuator is turning and all the linkages are moving, somehow the door may still be stuck/not opening all the way. Or maybe its just so cold here that its negating the heat from the heater (which I seriously doubt).

This seems similar to the issue I am having but I am not the best with electronics so I would like to get some insight before pulling the actuator.

Me to but
 

I think my heater core is blocked because as the engine warms up only one pose gets hot.