Max AC blows through defrost
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Elder User
Joined: Jun 2004
Posts: 629
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From: Tucson (Cortaro & I10)
Max AC blows through defrost
'93 Bronco. When I select max ac, within 1-5 seconds the unit switches airflow, and now my air blows out of the defrost vents.
Is this fixable on the HVAC unit, or will I need a new / newer one? Or is there something else (cheaper) to start looking at?
Thanks in advance! It's friggin hot here.
Is this fixable on the HVAC unit, or will I need a new / newer one? Or is there something else (cheaper) to start looking at?
Thanks in advance! It's friggin hot here.
CO River Rat
Joined: Feb 2004
Posts: 3,209
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From: Lake Havasu City AZ
If that Bronc has a vacuum-controlled valve that shuts off coolant flow to the heater core when you select MAX A/C, it or its hose may be leaking; if so, you lose vacuum and the airflow goes to Default (defrost).
Steve
Steve
Hotshot
Joined: Jan 2004
Posts: 19,762
Likes: 1,079
From: St Louis
It's also possible that your recirculate vacuum motor, the mode selector, or the vacuum line between them is leaking (perhaps disconnected).
Either Steina's or my suggestions are likely choices as they use the same vacuum circuit.
Steve
Either Steina's or my suggestions are likely choices as they use the same vacuum circuit.
Steve
Post Fiend
Joined: Jun 2002
Posts: 13,873
Likes: 3
From: Atlanta GA
By Federal law when something breaks in a heating system it is suppose to default to defroster mode. So, the first place to look in any vehicle is the vacuum system. If the vacuum fails, a spring pulls the vent closed to default to defrost.
On your vehicle, just remove the radio to get at the lines.
What you can do is buy a cheap brake bleeder and by connecting it to various lines you can change the modes. The valve on most vehicles is a round four post disc.
> Or is there something else (cheaper) to start looking at?
I think on the 1993 5.0/5.8L they still used a plastic can? I would put my brake bleeder there and force a good vacuum with the a/c switched to panel (vent) and see if they stayed there. You just might have a minor hose leak or cannister leak.
On your vehicle, just remove the radio to get at the lines.
What you can do is buy a cheap brake bleeder and by connecting it to various lines you can change the modes. The valve on most vehicles is a round four post disc.
> Or is there something else (cheaper) to start looking at?
I think on the 1993 5.0/5.8L they still used a plastic can? I would put my brake bleeder there and force a good vacuum with the a/c switched to panel (vent) and see if they stayed there. You just might have a minor hose leak or cannister leak.
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