1988 TC - Erratic blower speed.

[DerekTheGreat]

Howdy

Just noticed this last night. It's hot as hell, turned the A/C on but the fan stayed on the low speed position when on Auto. Cycled the speeds and it increased but when put on Auto it went back to low. Then I moved the temp slider around and back to 65 and it stayed on high until it cooled off enough. I have to repeat this cycle every time I use the A/C. What gives? I replaced the ATC sensor either last fall or the year before that with a Motorcraft unit...

Cheers,

Derek

[kishy]

I replaced the ATC sensor either last fall or the year before that with a Motorcraft unit...

When you say "ATC sensor" are you referring to the thermal blower lockout in a heater core hose? That would be my suspicion for something to check. Jump/bypass it both electrically and the vacuum ports, and see if issue persists.

[sly]

There's a position sensor on the blend door that controls the fan speed in auto IIRC. If that thing is getting crappy it'll do this. At least that what I'm thinking it is from the wiring diagrams I have. I need to get under the dash of my 88 and find that thing so it's not so much a magic box as it is a functional piece of hardware in my mind.

[DerekTheGreat]

When you say "ATC sensor" are you referring to the thermal blower lockout in a heater core hose? That would be my suspicion for something to check. Jump/bypass it both electrically and the vacuum ports, and see if issue persists.

I meant the blue thing under the dash pad on the passenger side. That thing you're talking about has been dealt with by me. Thought I fixed it, worked well for about a month and now floor doesn't work again. Going to bypass it but in a way where it still looks factory. Been lazy with that though.

There's a position sensor on the blend door that controls the fan speed in auto IIRC. If that thing is getting crappy it'll do this. At least that what I'm thinking it is from the wiring diagrams I have. I need to get under the dash of my 88 and find that thing so it's not so much a magic box as it is a functional piece of hardware in my mind.

Ah, I bet this is what my problem is. Where is it exactly and what does it look like? Is it repairable?

[gadget73]

Its right on top of the heater box. If you open the glovebox, you'll see the gold vacuum can that works the blend door. Shine a light in there, and you may be able to see the electrical gizmo hooked to it via a linkage. Not certain if you can get it out of there without tearing into the dash or not. Its just a switch, basically a modified version of what is in the climate control. Probably either its sticky or the connections on it are bad. Prob one of those "buy a new one" sort of deals, but you might be able to polish the contacts. Honestly its one of the very few parts I've not had to screw with so I don't know it's innards.

[Tiggie]

You can get it in and out of a Vic dash if you take out the glove box. Not sure about townie but there is a reasonable chance it should come out.

[knucklehead0202]

Aww crap. Does the same stuff apply to a '90 with the auto climate control? Mine works fine for now but I had a feeling the fancy shit would get me sooner or later. Old car had the basic a/c.

[kishy]

Aww crap. Does the same stuff apply to a '90 with the auto climate control? Mine works fine for now but I had a feeling the fancy shit would get me sooner or later. Old car had the basic a/c.

In summary: nah. That's the system I'm more well versed with and it's quite different. Works to accomplish the same goal, but does it differently. The most likely failures of the 90+ (I'm thinking it's more or less the same 90-94? control head may be more specific to 90-91 in faceplate only) system are the electronic blend door actuator and the thermal blower lockout I indicated earlier here.

[DerekTheGreat]

Its right on top of the heater box. If you open the glovebox, you'll see the gold vacuum can that works the blend door. Shine a light in there, and you may be able to see the electrical gizmo hooked to it via a linkage. Not certain if you can get it out of there without tearing into the dash or not. Its just a switch, basically a modified version of what is in the climate control. Probably either its sticky or the connections on it are bad. Prob one of those "buy a new one" sort of deals, but you might be able to polish the contacts. Honestly its one of the very few parts I've not had to screw with so I don't know it's innards.

Haven't checked yet but does it have a name and is it still available? Sounds like I've got about as good a chance finding one of those new as I do finding the ride level controller for rear air shocks...

You can get it in and out of a Vic dash if you take out the glove box. Not sure about townie but there is a reasonable chance it should come out.

Good to know. I found a townie glove box amongst my stash of chit while moving, which means if I can take that out of parts car without breaking it I've got a good chance of not breaking it on my car haha.

[gadget73]

automatic fan switch maybe? Not honestly sure. Its also possible that its a sticky linkage problem. If those parts don't move like they should none of it works right.

[sly]

Could also be weak vacuum source. Had that problem with the Mark and har to run a new feed line for the AC controls as the original one was kinked and cutting itself off.

[BigMikeIT]

Blower motor resistor? I had experienced speed changes or no medium.


Sent from my iPhone using Tapatalk

[DerekTheGreat]

Hrm.. I'll just have to rip it apart once it quits completely to see what's going on. If I manually switch the blower to any setting other than "Auto" the blower works as it should. Didn't drive the car yesterday and this morning it was cool enough that I didn't need A/C.

[gadget73]

The switch on the heater box works in parallel with the switch on the dash. If the 3 manual speeds work, then the resistor is most likely OK. It connects to the same terminals and such as the manual switch does. Vaguely possible that the dash switch is flaky since it has that "auto" position that sends power to the auto switch though. Might be a connector somewhere between all that.

[BigMikeIT]

Its right on top of the heater box. If you open the glovebox, you'll see the gold vacuum can that works the blend door. Shine a light in there, and you may be able to see the electrical gizmo hooked to it via a linkage. Not certain if you can get it out of there without tearing into the dash or not. Its just a switch, basically a modified version of what is in the climate control. Probably either its sticky or the connections on it are bad. Prob one of those "buy a new one" sort of deals, but you might be able to polish the contacts. Honestly its one of the very few parts I've not had to screw with so I don't know it's innards.

Is that the thing that you can see just under the lip of the dash pad? It looks like a bi-metallic loosely coiled spring (thermostat). I thought I read someplace years ago being what senses the cabin ambient air temp - for ATC.