Vent/Heater Intermittent...why?

onEdge24

Registered User
Well the last fer months have been my project time for the car of my dre...err nightmares :) My beloved 91 SC Auto. Let me preface this by saying I'm decent with tools, and great with directions, but until this car I haven't done this much under the hood work ever, so I am learning as I go. Thanks to every poster on this board who has saved me thousands of $$ in diagnostics and shop work and imparted knowledge in the 3 years I have had my SC.

Here's what Ive done so far thanks to this board. Replaced Power steering lines (all), replaced Accumulator, replaced IAC valve, Buying shocks and taking a deep breath as I look into putting those in, just replaced my motor mounts (yeah i can actually see light under the oil pan :) ) And then there was the extreme fun replacing my thermostat. Wish I could strangle the guy before me who bent out the housing.

So now im looking at my climate control and wondering what the hell is wrong with it. I can turn the heater/vent/deforster on and sometimes pow, here it comes full blast as it should. Other times I turn it on and....nothing, then during the course of the drive it sometimes comes on and works great.

So anyone out there help me troubleshoot this? If its a high dollar deal and not going to affect anything else, I'm probably just going to leave it as is and freeze during the few cold days we get here in Texas. AC hasnt worked since I got the car (worked on twice by shop and both times it was gone in 2 months again)

Any and all help apreciated.

Chris
College Station
 
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Chris,
Howdy to a fellow Texan. Not sure how much help I can be, but maybe another lead to follow. On my 94, my climate control has been goofy for a while. My problem is intermittent a/c. I found out you can get a trouble code off your climate control system by pushing a couple of the buttons at same time. Unfortuanetly, I don't remember the exact procedure. Anyway, my code came up pointing to a blend door problem. Unfortunately, to fix my problem I'm going to have to rip out the dash to get to it. So far, it hasn't been so awful that I can't bear it. Just sucks some in the summer when it decides to blow HOT air instead of cold.
I'm not sure which climate control system you have. Earlier models have slide controls that you have to push manually, if that's your set up then you'll have to use a different procedure to determine the trouble code.
 
Rick,

Thanks for the input. The controls on my SC are buttons for choosing which function you want: ac/heat/etc, and a slider for the force of the air flow from auto-->Hi.

Like I said, sometimes it works, sometimes not, No big deal til it really pissed me off this morning when I had ice on my windshield and no defrost. 1 broken ID later, I could sorta see out of my windshield.

Pulling the dash seems like a real PITA, especially considering I have no idea what I am doing when it comes to all that wiring in there.

Gig'Em
 
Vent/heat problem

If it is changing constantly from vent to defrost vents and back and sometimes changing with the speed and load of the car check the vac line that is under the glove box on the passenger floor board area. My SC was doing the same thing and I noticed it was off of when I was changing out the radio. it looked like it was attached to a canister or chamber that resembles a fuel filter. I havent had a problem since . In the area that it is in it could be kicked or pulled of with someones feet by accident. Hope this helps..
 
Well, it doesnt switch like that. It simply either works right or not, and theres no way to tell if its going to come on or not. Its almost like a short or something that sometimes has contact.

Problem is, I have no idea how to troubleshoot this and havent really been able to find anything that could point me in the right direction yet.

Thanks again

Gig'Em
 
When you say it doesn't work, do you mean that you can choose the function (defrost, heat, vent) and just not the desiered temp? If that's the case the blend door actuator is bad. To replace it, you have to rip the entire dash apart. Mine started spitting out e7 and e2 codes (blend door can reach endpoints and blend door can not calibrate), but after removing (and putting back) the memory fuse in the engine compartment it started working again. Although now if you adjust the temp to quickly youl'll hear a clicking noise coming from the actuator. So you might want to try the menory fuse to see if that works and also if you need the process for checking codes let me know because it's in my manual somewhere. Good Luck.
Mike
 
I thought Id said this, but i was tired last night and didnt.


When I say it doesnt work or it works intermittently, I mean that sometimes it actual blows air ( and yes I can control the temp as long as its not the Broken AC) and sometimes it wont blow any air at all when i turn it on, them maybe somehwere in the trip it will suddenly start blowing air.

Any help on pulling codes would be appreciated as well, but it seems it has the ability to work but somewhere either something is loose or broken that i need to replace and basically I dont have a clue where to start.

Thanks Again

Gig'Em
 
I guess that the blower is not working? I dont know, but that sounds right. I really dont know a whole lot about how the whole system works (I'm reading as much as I can using the search function). Would the blower not working or having some sort of short or something produce the effect im seeing?

I'm looking for someone to point me in the right direction so that i can look at it and maybe figure this out.
 
If you can control the output fuction of the system from defrost to heater or vents, then that part is working fine. If you can control the temp, then you blend door is working fine. Now if the only thing you have no control over is how much air is coming out the vents, heater or defrost, then the problem is with the blower or blower controls. It could be the switch for the blower or it could be the variable speed control for the blower which I think is mounted to the blower motor behind the glovebox. And I'm not exactly sure, but to replace the variable speed control, you have to replace the whole blower motor, because it may be one complete unit. Although I do remember someone saying that he picked up used one at a junkyard and was able to just switch the speed control. The best thing to do is to use a volt meter and test for voltage at the motor, speed control, and the switch at the heater controls. If you need some trying to figure out the wiring, it should be in my ford manual.
Mike
 
Chris,
If you run that climate control test, IT may shoot you in the right direction and give you an idea of what may be happening!!!

Calvin
 
Thanks guys, I found some other posts now that I have a clue what I was searching for and most of them also point to the blower motor or a related part. Im going to run the test tonight and try to take a look at the motor and wiring this weekend to see if I can make heads or tails of any of it.

Ill let ya know what I find.

Gig'Em
 
Still Looking

Well I ran the diagnostic using the FAQ and no error came back. it simply ran the test and then showed 88 with the centigrade and farenheit symbols next to it. The Faq said it would show 75 if the test was interrupted??? any different on a 91 SC?

I have noticed that the one pulley on the pass side bracket that has the interior piece engage and rotate with the pulley does not do so all the time or even much at all. Could this be my culprit? I am still looking things up so am currently at work and it just came to me and I have no idea what that part is.

Gig'Em
 
That’s the AC compressor.

Isn’t there a sensor that measures coolant temp so as not to allow the fan (blower fan) to come on and blast you with cold air?
 
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