When i am driving my truck and have the vents or a/c on and i give the truck about half throttle or more then the air stops coming through the vents and starts going through the defoster vents does any one know how to fix this.

thanks

 

when you gun the truck it stops the A/C to free up more horsepower.

 

Defrost is the default position if your A/C system loses vacuum for the mode doors. I wanna say there is a check valve that holds the vacuum in the system, that may be damaged. Others will chime in for the location of it.

Aaron you are correct that the A/C compressor will kick off at WOT but that is not his issue.

 

My truck will drop the ac at anything over 3k.

if you have a small leak in the supply line going to the vaccuum res it could cause that problem.

the res is under your airbox

 

It depends on the year. Earlier Rangers have a separate check valve. In more recent years, the check valve has been built into the vacuum reservoir under the airbox. I believe his 2000 is the later kind with the integral check valve.

It could also be a minor leak in the vac system to the HVAC controls. This could allow the controls to work normally during high engine vacuum conditions but revert to defrost when the vacuum is lower.

The OP doesn't say if he has 4WD or not. During 1998 ~ 2000 1/2, the vacuum reservoir on 4x4's was used by both the HVAC controls and by the Pulse Vacuum Hublock system. The PVH system is notorious for leaks and sometimes causes the AC discharge problem at WOT.

 

Only Ford could design a vehicle where a front 4wd hub failing causes the interior HVAC to switch to defrost mode. :)

 

Sharing the vacuum reservoir and check valve between two systems would be an efficient way of doing things. Unfortunately, the Ranger PVH system was designed and manufactured by Warn Industries and it didn't live up to Ford's expectations. I'm sure that's why it disappeared midyear 2000.

 

sorry about not saying it was a 2000 2wd 3.0

 

not in my 93...I never heard of any doing that actually

 

Well, that eliminates the PVH system and makes your job easier. Look over the vacuum lines, especially the one between the spherical black vacuum reservoir (below the air filter box) and the HVAC plenum on the firewall. It can get melted if misrouted or it can get damaged during servicing. Then check for leaking or disconnected vac hoses up under the dash on the passenger side. If all of that's OK, you may have a cracked vacuum reservoir or a bad check valve in the reservoir.

 

my ranger never does this but my old 96 s-10 had the same problem with the a/c coming out the defroster when getting on the throttle

 

Is there any way of testing the system to see where the leak is
Thanks this is a very good forum i have learned alot about my truck on here

 

I was looking into the exact same problem today. I have been noticing my a/c would stop then come back on. I don't knwo if it is when I floor the truck or not. But when it went off I turned the air to max and noticed it was comming out of the defrost.... My truck is a 2000 2.5 2wd. Weird. I'll look into what was said tomorrow and see if i can find the problem.

 

yeah about a year ago when I had to replace my slave cylinder, i took the fender wells off to get to some of the tranny bolts.. and had to take off that vacuum reservoir and when it came time to test drive the truck (didnt put the wheel wells back in) and forgot about that reservoir just hanging there, the tire burnt one of them clear in half and every thing came out of the defrost vents.. I tried to patch it up with some aquarium tubing and silicone sealant (i know it isnt good for the engine..) and still everything came out the defrost vents.. So i ended up just replacing that vacuum line with some from Napa (at the DEALERSHIP, you have to buy that whole reservoir and other vacuum lines if you want just one piece of vacuum line).. so moral of the story, like said above, if there is ANY kind of leak it'll just go to the defrost vents..

 

You could buy the Mighty-Vac to test your vacuum system with the engine off.

It's marketed for bleeding brakes, but has many other uses.

A golf tee can be useful for plugging lines while testing.

 

I just looked at a few areas mentioned, and under the air intake, there is a ball, almost like the float in a toilet. It isn't screwed to anything, just hanging there. I take full responsibility for that b/c it was on the wheel well, and i took those off when I put the lift on. So maybe that is cracked, and also a line about the ball looks to be cracked. I really don't know what I’m doing. I know about a/c from my summer job, but it’s hard for me to follow anything in the hood, and I mainly pipe them in at work... As I search around more inside I'll keep yall posted on what was wrong.

Thanks to everyone for showing me where to look.