Stuck on defrost

***lilgreen*** · #1 (**permalink**) 03-04-2012, 05:18 AM

I'm having trouble with my A/C. The vents are stuck on defrost no matter what configuration the heat or A/C is in. I have checked all the fuses and relays and can't find anything wrong. The control panel works as advertised but the position does not change. Any help would greatly be appreciated.

jesilvas · #2 (**permalink**) 03-04-2012, 05:30 AM

You have a vacuum leak.
Is it 4wd? If so, check the vacuum lines going to the front hubs that lock them in if you have auto lockers.
Also, on one of the heater core lines, there is a vacuum valve. It keeps the heater core blocked off with Max AC running. That line likes to fall off and you lose your vacuum there.

***lilgreen*** · #3 (**permalink**) 03-04-2012, 01:27 PM

Thanks for the response I will take a look and see what I can find.

raptorfever660 · #4 (**permalink**) 03-11-2012, 09:17 AM

I had the same problem on my truck. If you open the glove box and squeeze the side together and allow the box to hang you will a vacuum solenoid. Take you hand and raise the lever up while the HVAC system is on vent. It should hold its self on vent if not your not getting vacuum to solenoid. If it does you could need a new solenoid.

***lilgreen*** · #5 (**permalink**) 03-15-2012, 10:18 AM

Well I got my vacuum pump from rock auto in today. That was definitely the issue. I still have a vacuum leak in the 4 wheel drive system but the air flows like it should now. All that is left to do is find the vacuum leak and the 4 low will work again. Thanks for the good info.

mint-6oh · #6 (**permalink**) 03-15-2012, 04:41 PM

A vacuum leak will not cause 4 low to not work. All they use vacuum for is to lock and unlock the hubs if its auto.

DoubleDpsd · #7 (**permalink**) 03-15-2012, 04:57 PM

Quote:

Originally Posted by mint-6oh

A vacuum leak will not cause 4 low to not work. All they use vacuum for is to lock and unlock the hubs if its auto.

^^This.

I have a vacuum leak, everything through defrost. I just have to turn hubs to 'lock' and 4hi and 4lo work like they should. 4hi and 4lo aren't tied the vacuum system, just the hubs like stated.

Question though, could you hear your vacuum pump running while you were in the cab before you started it or was the pump silent? How did you diagnose it as a bad vacuum pump? Thanks

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