heater stuck in defrost

[ogrehauler]

I cant figure out why my heater will only blow through the defrosters. I have checked the diverters under the dash and none are stuck also checked air pressure from the lil compressor under hood and hoses up to the control panel. tried blowing air to see if there wasnt enough coming out the compressor. could the control panel be bad cause when I flip it to air cond. it will blow cold but through defrosters... kinda useless.

[diesel_19]

mine did the same thing there was a plug in under the passneger side dash by the floor unplugged.i plugged it back in and it took a couple hours for the vacum to work but now everything works hope this helps you out.

[ogrehauler]

thanks but i tried messin with that already. if I can't get this figured out I might have to get out some tie wire and wire the floor part open.

[diesel_19]

that would defenitly work.lol

[GregsSD]

The little compressor under the hood is a vacuum pump, not an air compressor. And if you have a vacuum leak somewhere or if your vacuum pump is not working then the system automatically diverts the air to the defrosters.

Check to make sure your vacuum pump is coming on, if you turn your key to "run" without starting your engine then you should be able to hear it run for a short time while it builds up vacuum pressure.
If it doesn't then check for blown fuses and check to make sure power is getting to the pump. If it keeps running all the time then you have a vacuum hose that either came off somewhere or a cracked vacuum hose.

[ROLLTIDE72]

I am having the same problem but it comes and goes and somtimes the temp control knob dosnt work. I know the vacuum lines to the locking hubs are known for going bad and I think this can eventually lead to it only coming out the defrost.

[rsecondchance1]

Most of us have had the same problem or are going to,as stated above, you most likely have a vacuum leak. There are lots of ways to do this but I found that if you pinch all except the one that feeds your defrosters, and see if they work after that. Then one by one unpinch the tubes and see if your vacuum motor will build vacuum and stop runnning,continue until you find the one tube that keeps your pump running. Trace those tubes to the problem area. Takes time so take your time.

[PowerSTOKED_Bryan]

where is this vacuum pump under the hood?

[bcoutsfly]

Mine does the same thing. I dont know if this will work for you but it solved my issue. Turn the ac/heater off and put the fan on the lowest setting. Turn the heater/Ac back on and slowly turn the fan up. I have to do this everytime I turn my ac or heater on.

[PowerSTOKED_Bryan]

ill try that. im just wondering where the vacuum leak is. it happened once and stayed on defrost for a couple days, then i manually locked my hubs, got into the truck and i miraculousy had heat at my feet. i figured that the leak must be on the vacuum hubs. i unlocked the hubs and heat worked great for a couple days, now it doesnt work. ive tried locking, unlocking the hubs, still nothing.