Rep Power: 0

i have a 1999 civic lx. when I turn the **** to defrost the ac light does not come on and air does not come out of the defrost vents. I don't know what is going on and wondering if there is a fix that I can do myself. what is the prob.

 
Rep Power: 204

Even when it is set to defrost the AC won't come on until the fan switch is turned. Do the fans work at all? Try the fan switch at all settings and tell us the results.

 
Rep Power: 0

when switching it to the defrost mode the ac should automatic turn on and it does not. and the air does not blow through the defrost vents at all. even if manually turning on the a/c

 
Rep Power: 204

In my 99 Civic the AC does not come on in defrost mode unless the fan switch is turned on (and the fan is working). If your fan only works at it highest setting then it's probably the power transistor. If your fan doesn't work period then fuse,blower motor, input power to the blower. If your fan works intermittently then fan switch.

...but your problem is fan related not defrost/AC related.

 
Rep Power: 0

and yes the fan works in all setting except on defrost. the front wind shield does not get any air

 
Rep Power: 0

ok, so when you have the selector set to blow on your feet it blows just fine.... Same with the front facing vents. But you turn the defroster on and.... does the fan stil blow and the air just isnt coming out on the windshield? or does your fan turn off when you select defrost....

I believe the selector is vacuum operated... might start checking vac lines under dash if the fan stil blows on defrost but the air just isnt diverted to the windshield. However if the fan turns off when you select defrost you have other issues.

Give us more info so we can help you better/easier.

 
Rep Power: 518

This uses electric servos. No vacuum.

 
Rep Power: 0

sorry took a while to read. you are right the air come to the feet when selected and then to the upper or face and then when turning it to the windshield there is no air coming out. and it is electrical not vacuum

 
Rep Power: 518

Is the fan still operating at that time?

Where is the air coming out? (floor outlets or dash vents)


Got a friend with an identical car that works right? Swap the HVAC controller and see what happens.

 
Rep Power: 0

the air does blow not the dash vents by the windshield but the ones by the doors. and it will at the feet

 
Rep Power: 518

At this rate, your cold season (if you have one of those) will be over before you get this problem figured out.


I'm sticking with this guess: Locate a known good HVAC controller to swap as a test.

 
Rep Power: 0

Have the same problem with a 1999 Civic DX. The, now wife, says the windshield defroster stopped working when the windshield was replaced. Do not see any correlation there.
Air does blow out the vents at each end of the dashboard to defrost driver and passenger side windows. The side windows do clear up after short time when frosted.
Guessing I also need to check into a HVAC controller.