A/C stops blowing through vents as i accelerate - Ford Forums

redass1876 · 07-09-2009, 15:07

Vehicle: 2002 F-150 Harley Davidson

This started just the other day when i was trying to use my A/C.

I was sitting stopped, turned on the A/C and it started blowing nice and cold as normal. After i started accelerating, the flow through the vents slowed and finally stopped. As it stopped, i heard the compressor kick into overdrive (like it does when it is cooling the air before blowing it through the vents right as you turn it on.)

would this occur due to the air not being cool enough and it trying to cool it instead of blowing semi-warm air through the vents or is this possibly some sort of vacuum problem?

any help helps... thanks

1meanGT · 07-09-2009, 17:43

I agree with your thoughts of that it is vacuum and would recommend checking the vacuum canister or the rubber hose going to it. It acts as a vacuum reserve for low vacuum conditions such as when the throttle is mashed. I think it is on driver's side.

They are usually cracked from a car accident or someone drops something on them. I can't tell you how many times I have seen this.

redass1876 · 07-09-2009, 20:48

i understand that when you accelerate (any increase in RPMs really) but it even occurs at a constant speed as long as its above ~30 MPH

i figured holding a constant velocity wouldnt draw any extra vacuum pressure

even considering that is the canister/hoses leading to/from it something worth checking?

edit: also, i tried revving up the engine while it was parked and the air kept blowing as it was supposed to.. this makes even less sense to me

thelittle289 · 07-11-2009, 08:07

is it 4x4. i don't know about 150s, but 250 & 350 auto hubs work off of vacuum and if the hose gets a leak it will make your ac come out the floor and defrost.

1meanGT · 07-12-2009, 10:53

Sometimes it is hard to diagnose or put sense to everything till you know all the symptoms. Assumptions are made as I do not know if you have limited knowledge or access to tools. I am guessing you want to try to fix this problem yourself.

There is one statement that I am unable to follow you on. It is with the A/C compressor. The compressor will cycle on and off as needed based on the pressure that it needs to keep the system performing. So I am not sure I know what you mean by:
"As it stopped, i heard the compressor kick into overdrive (like it does when it is cooling the air before blowing it through the vents right as you turn it on.)"

Right now, based on what I am trying to piece together, the following may contribute to what you have described:

1. You have a vacuum leak.
2. Your A/C system pressure is low.
3. If you have a digital climate control, the system may have a problem- but may be reacting to #2 by turning the fan speed down.
4. Broken blend door.
5. undetermined yet.
6. The Gremlins are back.

I would recommend to start your diagnoses with the vacuum canister and or checking all vacuum hoses - even the one that is on your brake booster. If you don't want to remove hoses or find locations hard to inspect or check, purchase a spray can of carb cleaner. Spray it over the canister or hard to reach vacuum locations to see if the engine speeds up from an idle. If it does, it indicates a leak as it sucked in carb cleaner. Be careful around hot headers- fire risk if you use too much.

The easy way is to hook your engine up to a vacuum gauge which would indicate whether there was a leak or not to start off with.

If you start with this and report back, I am sure others will help chime in to provide some better direction.

Tommyp · 09-04-2009, 20:49

Small vaccum pump located behind battery bolted to front fender controls blower door.I replaced mine an everything is fine now

Grant218 · 09-07-2009, 22:42

i used to have that same problem on my ford taurus

Steve83 · 09-10-2009, 11:24

Look for degraded vacuum lines near the battery, esp on the lip of the firewall.