I have a 2001 F150 crew cab. About 2 years ago I started having issues with the heater and after about $1200 at the Ford garage it worked. When spring came the AC didn't work. Another $1000 to Ford got that working for a while. I now realize the problem isn't with the heater or the AC but with the air getting blocked. At this point the heater or AC seems to work OK for an hour or 2 so short trips aren't a problem. On long trips though, after a couple of hours the amount of air coming out of the vents slowly decreases until it stops completely. I can still hear the blower going but feel no air coming out of anywhere. If I let it sit for several hours or overnight, it's OK again for a while. I suspect it is the "air supply door" and my question is: Can I get to it and hopefully repair it without removing the whole dash? I would even he content to just force it to stay in the open position. I understand it is vacuum actuated so it might be as simple as a vacuum leak.

Thanks in advance to all from a forum newbie.

 

Is the air blowing out a different vent? If so you need to look at the doors that switch the air flow but one vent to another. I'm not familiar with the air system on the F150 but I had that problem SEVERAL times in my Diamonte and it was always the flapper/door. It has a plastic pin that rides on a slot and it would get out of the slot and couldn't move. Once I got the assembly out it was simple to pop the pin back over where it should have been.

If the air isn't coming out anywhere that you can find (and the blower is running) then there's probably leaves or a mouse nest or something else plugging the system. If so then you'll just have to start taking things apart until you find it. I would start with the blower motor IF it's not too difficult to get to. I had to take that out of my daughters car several times and clean the leaves out of it.

"On long trips though, after a couple of hours the amount of air coming out of the vents slowly decreases until it stops completely."

It sounds like the system is getting too cold and the condenser is freezing up. Check the drain on that thing. Also get someone that understands AC systems to check the hi and lo pressure, they should be able to tell if there's a problem. But regardless that shouldn't affect the heating system.

For that kind of money, the stealership should have replaced the whole system and FIXED the problem!

 

Your evaporator is icing. This is the ONLY thing that will cause a gradual and consistent loss of airflow. You can prove it by seeing how much water is sitting under the truck a few hours after it was parked following a "no airflow" episode.

Usually, it's the compressor staying engaged when it shouldn't, often due to a stuck low pressure cycling switch. You can switch to VENT periodically and it will probably keep clear much longer if the compressor clutch is working properly.

 

Thank you for the input. I don't think it's the compressor freezing up or blockage in the air flow. As I stated, When I first start it (after it being off for some time), everything is OK, in the winter I get heat and in the summer I get AC. The problem starts after about an hour or 2 of continuous running, the air flow from all vents starts to deminish until eventually there is no air flow at all from any vent but the blower is still blowing. After it sits overnight (or some period of time) it's OK again for a while. I don't notice it at all on short trips. I'm thinking the air supply door is somehow closing by itself but I'm not sure where to locate it. Troubleshooting would require that I remove the entire dash unit which I'm not too keen on doing unless I absolutely have to.

 

Does it ever do this when you're NOT using the AC? Your description sounds exactly like the evaporator freezing over with ice. But as I said, a knowledgeable AC guy should be able to diagnose that based on the low pressure reading from the AC system. FYI The low pressure reading translates directly to evaporator temperature so he can tell if it's too cold. If it gets too cold it will freeze the condensation (humidity from the air) instead of letting it drain and that will gradually build up until it completely blocks the air flow through the evaporator. And as you noted that takes hours to thaw and drain. Tell me, after you park your truck and turn it off, do you get a lot of water draining out of the evaporator? A small amount would be normal but if it's frozen over you'll probably see a lot of drainage over the next several hours.

FYI 2. The expansion value controls the amount of freon going into the evaporator and hence it's temperature so if it is freezing over that's most likely the cause. It could actually be a bad valve or it could dirt or other contaminate* in the system that is affecting the value. Trash, leaves, hair, etc in the evaporator will make the problem worse since they soak up and hold water so that it freezes instead of draining out as it should.

Frozen evaporators are a common problem here in Florida due to our high humidity. Where are you located?

One thing that I have done with a freezing evaporator here in Florida is to turn off the AC compressor as soon as I notice the air flow decreasing but leave the fan running. IF I do it before the evaporator freezes up completely, that will force un-air conditioned air through the evaporator and melt out the ice in 20 minutes or so. Then I can use the AC again, at least until it starts to freeze over and then I have to repeat the process. But at least if gives me some AC! If the evaporator was indeed freezing over, I notice that even after I turn off the AC compressor that the air coming out of the vents is still somewhat cold due to the ice on the evaporator. That's another clue that might help you figure out if freezing over actually is your problem.

*Any air or moisture left in the AC system can freeze and cause problems like this. That's why when you have an AC system open you need to (1) replace the dryer and (2) pull a GOOD vacuum on the system before refilling with freon. Do as the shop manual says and pull a GOOD vacuum with a vacuum pump and not one of the air hose gadgets and let it run the length of time that the manual says so that you get ALL the air and moisture out of the system.

 

There are NO doors that would cause a blockage of airflow as you described.

It's an iced evaporator. See both the previous post and my last one. If you insist on SEEING the chunk of ice,next time it freezes, rip open the plenum and look at it. Or you could simply accept that it's happening and fix it.

 

I would go along with the explanation of the freezing evaporator except for the fact that in the winter the same thing happens but in this case, the heat stops coming out of any port no matter where the selector switch is placed. Again, it works fine initially but after a while the blower is still blowing but the air output decreases to nothing.

 

Sigh... Take it somewhere and PAY for the same opinion....

The evaporator is the ONLY thing that ALL airflow must pass through REGARDLESS of output or input air selection or temperature setting. I told you in post #3 what the usual culprit is.

 

That's VERY odd! But I'm with SHO89, THIS has got to be a freezing evaporator. I just don't see how a door would gradually close and gradually block the air flow. But you may have to take the system apart and check all the doors and ductwork to be sure that they're not closed or plugged up. And SHO89 is also right in that the air always flows through the evaporator even when the evaporator shouldn't be cooling it. The cooling function is controlled by turning the clutch of the AC compressor off or on. I wouldn't think the compressor would be turned on in the winter but who knows on some of these crazy, newer systems! You MAY also have an electrical short that supplying power to the compressor clutch OR a clutch that's not disengaging. I would check for that before doing anything else.

"Sigh... Take it somewhere and PAY for the same opinion...."

He's already done that, TWICE! Sometimes you're just on your own when it comes to finding or fixing difficult problems!

 

There is no indication that either of those service visits were to address this issue. Perhaps one of them even caused the current problem by installing a defective part or a bum clutch that won't disengage.

Troubleshooting this is NOT rocket science. All that needs to be done to start is to monitor the low side pressure and to visually observe the clutch plate to see whether the clutch is remaining engaged when it shouldn't. Any competent A/C technician should be able to diagnose and repair this in short order unless there's a weird wiring or control concern.

 

I agree. It's largely a matter of being persistant, observant and taking nothing for granted.

 

In Winter the compressor is used in defrost mode, thus still freezing the evaporator.

For S&Giggles, do you have manual controls or digital control head?

 

I have manual controls.

 

Hi RAHebert45. Have you solved your problem because I have the same problem and I do not know what to do.

http://www.fordf150.net/forums/viewt...734447#p734447

 

I seem to have resolved the issue temporarily by pulling the fuse for the air conditioner. Apparently the AC was running all the time although I was unable to actually see the compressor with everything else in the way. I did that several months ago and had no issues with the airflow with the heater running. Since warm weather is coming now I need to find out why the compressor is running all the time.
Thanks to everyone who responded to my cry for help.