Hey everyone, this is the problem I am having with my 01 SCREW, finally want to do something about it. When I am running the A/C and coasting it works great and blows through the dash vents just as it should. Under hard acceleration though, the A/C automatically switches to blow through the defrost vent, when I ease up on the gas pedal it switches back to blowing through the dash vents. I have seen this same issue on two other Mercury (Ford) cars. Is this something normal.

 

yes its normal... your compressor will shut off under hard accel or when pulling hills. If there is HP being used somewhere and the engine needs it, it will override and take it back.... and it going to defrost is a default, cause the most important thing is to see, not be cooled off

 

i'm pretty sure the defrost vent is the default if no vacuum is present. check for a vacuum leak. check the vaccum line that goes to the vacuum motor for the airflow control door.

edit: did it just start to do this or has it been doing it?

 

You have a vacuum leak somewhere. There is nothing that will override your **** setting in your 01 except vacuum. My 01 runs just fine even under load.
The only exception may be if you have the electronic climate control module.

 

Agreed, a vacuum leak is causing the switch to defrost. Look for a leak in the tanks behind the battery tray. The line coming out of the firewall may have a T fitting with one side going to the tanks and the other to a hose leading to the engine.

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the switch for the compressor would simply disengage the a/c clutch it wouldnt change the air flow, its simply not going to gain anymore high pressure and the low pressure will rise, for the few seconds on acceloration, if it has the switch, i thought they only had these only 4 bangers tho, since they had such little hp...

 

have em all the way up to big rigs.... all about economy... however, as a fail safe on rigs if something is changed within the air ducts, it will default to defrost since that it top priority of the entire HVAC system

 

But the 01 F150 only defaults to defrost when vacuum is lost. The clutch switch only disengages the compressor.

 

right. he may have a blend door problem

 

Check for a leak in the vacuum line behind the battery, that goes through the firewall into the cab. They break or split there quite often, causing the problem you described.
If it is leaking there just cut out the bad part and repair with similar line.

 

I have owned my truck for 5 years now and it has been this way since I got it.

 

The blend door is not vacuum actuated. When you accelerate vacuum is lowest. That is why there are tanks to store vacuum when accelerating to keep the system from defaulting to Defrost. Most likely a tank is leaking or a line to it. That would explain why at part throttle when there is plenty of vacuum the system is normal. Under acceleration the tank or a leaking line to it is allowing the system to default to Defrost.

Regards

Jean Marc Chartier

 

The vacuum reservoir on my 97 and 98 is out inside the right fender. I have had to do repairs there before.

 

https://www.f150online.com/forums/hv...buildable.html its a vacuum leak somewhere, i didnt find one in any lines so i assumed it was in the eatc and i found a site where a guy replaced the orings in his and it worked , so i changed mine and it fixed the problem

 

hey guys i have a vacuum leak. its those small vacuum tubes/lines behind the battery. Where can i get new ones?