airflow control in HVAC box (Page 1/3)
JohnEStark JUN 08, 02:44 PM
Can anyone help me with a set diagnostic first steps to see why my cold A/C only blows out the floor and defrost vents, no matter which blend door button I push. 1987 Fiero GT, v6- 5sp-- w/ factory air cond. ? New owner, I've had the car two months.
Patrick JUN 08, 04:33 PM

Can you get air to blow out the center vents when the A/C is not on?
Spadesluck JUN 08, 04:39 PM
It could just be an easy fix. There is a plug that controls the motor for that airflow that goes to the bottom you can see from the passenger side footwell. Its sits in the middle , mine was cut. Had to rewire a new plug.
br1anstorm JUN 08, 05:10 PM
An answer to Patrick's question will help the diagnostic process. The direction of airflow is determined by flaps in the air-ducts (below and behind the dash) which are moved by motors controlled by the push-buttons for Heat/Vent/Demist/Norm/Bi-level etc. These flaps ought to move to direct the air to screen, dash-outlets or footwells whether the a/c is on or off.

A common problem that seems to come with age (I have the same issue in my '88 Formula) is that the little motors don't work too well. Sometimes they stick and the flaps don't move. Sometimes for some reason the flaps only move (you can hear the whirr-clunk) when you first turn the ignition on, and pushing the buttons while you drive along has no effect. It sounds as if your HVAC flaps are "stuck" in the position which directs airflow to screen and footwells rather than to the dash-vents.

I don't have an easy fix to suggest. Access to the motors and flaps seems to be difficult, and it's not easy to figure out where and how to spray WD-40 or similar to ease matters. Maybe other forum members will have solutions to offer?
Patrick JUN 08, 06:41 PM

quote
Originally posted by br1anstorm:

These flaps ought to move to direct the air to screen, dash-outlets or footwells whether the a/c is on or off.



Exactly. IMO, mentioning A/C only serves to muddy the waters in regards to air not being directed out of the dash outlets.... unless for some reason this only occurs during A/C operation.

[EDIT] It's probably worthwhile being made aware if the heater/HVAC unit is A/C equipped or not, as there may indeed be some slight differences in the hardware.

[This message has been edited by Patrick (edited 05-31-2020).]

theogre JUN 08, 08:02 PM
AC/Heat control board Switches operate 2 motors.
2 motors route air to outlets.
control board or motor(s) problems cause the above.
See my Cave, Heat & AC

Note: Board has 2 small "Coins" that limit power to the motors. (NTC or PTC Thermistor I believe) If fried, the motor connecting to it have problem itself or w/ door(s) they moves or dead.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

JohnEStark JUN 11, 04:01 PM
First of all to the Ogre: Thanks for the write-up. Next Saturday I'll start in checking stuff with a lot more confidence, and a lot fewer false starts down the "is this the place I need to work" path.
To SpadesLuck: I hope you are right. It is a new to me car in April, There was no need to use the a/c other than a couple of minutes at the car lot to see if it worked. I know the compressor works, I think the blend doors worked then. I added a performance sound subwoofer and a bluetooth phone radio, so I had that area apart and could have pulled something loose.
(DOES ANY HAVE PICS of the blend door electric connectors?)

FYI to all (thanks for the suggestions) the fan motor control works normal. there is never any change in the blend door/airflow behavior. No clicks/whirls/etc. at start up, no sounds across the entire HVAC button row, no sounds when I shut off the engine, and nothing I do from the drivers seat (or elsewhere) causes a change in the airflow path (stuck on blowing out the defrost vents, windshield and both side windows)

Thanks again, on Saturday I'll crawl into the floorboards with at least some idea of what I am looking for. I'll keep you updated.

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John E Stark

br1anstorm JUN 11, 07:18 PM

quote
Originally posted by JohnEStark:

...... the fan motor control works normal. there is never any change in the blend door/airflow behavior. No clicks/whirls/etc. at start up, no sounds across the entire HVAC button row, no sounds when I shut off the engine......




This information is a bit puzzling. My analysis might be simplistic, but I'm trying to be methodical. It seems that either

(a) the electrical buttons on that panel are faulty and have bad - or no - connections to the things they are supposed to control; OR

(b) the controls in the dash panel are fine, but the motors that move the vent-flaps are dead, or the flaps themselves are stuck in one position.

If (a) is the problem, how come the fan-speed control works normally? (it may of course actually be wired as an entirely separate unit). And how does the a/c actually kick in - since that is activated by the Max/Norm/BiLevel buttons? Is the a/c permanently on? Does the "Off" button work?

If (b) is the problem (and the fact that the fan-speed control works suggest that at least some of the controls are OK) it should be possible to switch the a/c on and off, even if the direction of the airflow can't be adjusted between screen, dash vents and footwells.

Seems to me the next step is to try to narrow down whether the fault is electrical and with the buttons of the control panel unit, which is easy to see and - I would think - to remove/replace; or whether the problem is with the motors and flaps down in the ducts behind and under the fascia - where the issue could be electrical or mechanical.

Best of luck in your ongoing investigations.....
pmbrunelle JUN 11, 08:13 PM

quote
Originally posted by br1anstorm:
If (a) is the problem, how come the fan-speed control works normally? (it may of course actually be wired as an entirely separate unit).



The blower fan works independently of the buttons.
JohnEStark JUN 12, 10:19 AM
Feeding information into the diagnostic forum team while waiting for Saturday to come around.

In regard to electrical behavior of my HVAC control buttons. Any of the three AC related buttons (Max. Norm, B/L) will activate the AC compressor. Pressing the OFF or any of the non-AC buttons (vent, HTR, defrost) will turn the AC off. Regarding the fan, Lo, 2, 3, Hi all run the fan as you would expect them to, in any of the six button settings. The Cold---Hot slider seems to be working, (Cold air comes out of the defrost vents) but hard to know exactly since we have never had dash vent airflow and a long enough ride to prove it in the real world.

I think that answers all current questions from "the team". We are one day closer to diagnostic Saturday. Thanks for the help. I'll do my best to photo the process on Saturday.

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John E Stark