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HVAC Malfuction.

625 Views 4 Replies 2 Participants Last post by  amunderdog
Drove the Seville yesterday, the lady of the house normaly drives it.
Something has gone wrong with the HVAC system and i am confused about where to start looking.

I get going down the road and notice it is on defrost setting, that was not needed so i selected auto.
It went to blowing heat (from dash vents? I do not remember) until i thought i would loose my mind.
Later in the day it switched over to AC blowing out of the dash vents.
that persisted for rest of the day, I even tried economy, that setting was all weird also.

The outside air temp reading seems correct and the control panel seems to be functioning.
No trouble codes for the HVAC system.
Things that come to mind.
Vaccum leak?
Blend door malfunction?
That controler box thingy with all the vaccum lines?
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If I am understanding you correctly, it was set on dash (or floor) and reverted to defrost on it's own. Pretty sure yours is still vacuum operated and defrost is the default setting. I'd start by looking for a vacuum leak. Remember, the parking brake release is on the same vacuum circuit, so be sure it releases when put in gear. I not, it's probably a ruptured diaphragm. If that's not the case, check all the under dash vacuum lines as well as the line on the firewall to be sure you have vacuum to the cabin.
So I checked vacuum - quick cursory exam.
Emergency brake is releasing, could not spot an obvious vacuum leak.
I can cycle output defog and auto (which should be mostly floor).
So it seems to be down to why it was blowing out the dash vents when auto or econ selected.
Auto lets the car select the mode.
ECON is auto with the A/C bypassed.
If it was warmer in the car than outside, it was probably in the cooling mode and switched to dash vent.
Could be.
It is a real mystery for me.
I cannot remember any of ours being uncomfortable to ride in due to the HVAC.
Burned up in the morning then cold the rest of the day.
Usually the dash vents blow little if any air, it is more ambient atmosphere than blowing on the occupants.
On our 93 thru 95 models there is no vent mode selection to speak of.
As far as output modes, you can request Defog, de-ice or select a temperature that makes you happy and let it decide what to do in ether auto or econ.
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