f150crewcab

My air conditioning is intermittenly blowing out the defrost vents. It seems to do so when I'm accelerating, which makes me think its a vaccum leak; at least that's what I read as a proximate cause in other posts. Also, the a/c is running warm, so my questions are:

1) likely vaccum leak?
2) how do I test/find the leak? most likely spots to check?
3) would the vaccum leak also explain the hot a/c or do I need to recharge?

Thanks for the help.

Scott

rtg143

That's probably a vacuum problem. A leak in the lines, reservoir or check valve. As for the A/C, when it's on, does the compressor come on and stay on quite awhile?

kingsandman

Blend door would explain problems. Have fun, I just did one, BIG job!

f150crewcab

rtg143 - how do I check for vaccum leaks? Look for cracks? Special tool? Is this really a DIY job? I'm not sure how long the compressor stays on...I'll have to pay attention to it.

kingsandman - what's a blend door? Or where is it?

Thanks again.

rtg143

The blend door changes from cool to heat. First get the proper air flow and then check that. It's in the center/right just above the trans tunnel. When there's no vacuum, the system defaults to defrost for safety reasons. When you accelerate, the vacuum drops and without a reserve, it goes to defrost. I'd check the vacuum lines at the intake manifold to the check valve and reservoir under the hood. Then go inside to check. If you have a hand vacuum pump it helps.

kingsandman

The blend door's are famous for failure on these trucks. It's controlled by a servo that acts as the "male" to the blend door's "female". They split around the end and you lose control of your heat. If you accelerate hard or brake hard the door flops around from hot to cold. Another symptom is luke warm heat or poor A/C. If you pull the panel at the bottom of your dash right above the trans tunnel, you can get to the motor. If you pull the motor and plastic pieces fall out, you'll know it's the door. There's numerous threads on here showing it. Hopefully not your problem, but it could be by what you're describing.

baldtire

Visit heatertreater.net, (and no I'm not a employee of that company) they have a blend door replacement kit and a fix that they say can be done in a hour without taking out the whole dash, theres lots of instructions and videos on the blend door replacement.

kingsandman

I looked at that but I just couldn't bring myself to cut open a dash. I'd take it apart and change the heater core while you're in there.

f150crewcab

Thanks for all the advice. I'll be checking the vacuum lines first (and likely getting a vacuum pump to assist).

Does anyone have a vacuum line diagram? I've searched...unsucessfully.

rtg143

The Ford manual I have only shows each circuit separate. The only way I would test it is to start at the engine and check all the vacuum lines. One will go into the passenger compartment toward the passengers side of the firewall. There's also a reservoir under the hood. There's also a tee in that line.