Hey y’all,

I have a 2001 F-150 Lariat SuperCrew with the manual climate control switches. I am having a strange issue with what sounds like the HVAC mode switch. When it is in the off position there is a vacuum leak, but in any other position it disappears and the idle comes down to the proper rpms. All positions blow out of the vents as they should and the temperature changes properly as well. I have pulled the unit out and inspected the vacuum lines going to the switch and they all appear brand new. I know there are several vacuum check valves and controls on the firewall, so I’m wondering if it would be a check valve somewhere perhaps or the switch itself. I apologize, I forgot to mention that I have the manual controls. Thanks in advance!

 

Welcome! You need to tell us your year, make and model.

 

You also forgot to mention what you are working on.

Year and model such as 1997 xl or 2003 fully loaded beast.

 

Thanks y’all! I apologize, I edited the post.

 

Well, don't turn the **** to OFF, just leave it in any of the other positions.

 

I saw this earlier and wondered how you knew it was a vacuum leak. Seems like you might have assumed because the idle RPM went high, old-school vacuum leak diagnosis. But the PCM and IACV should have acted to drop it down.

Could be it is a big vacuum leak and the system couldn't fix it. Can't say. A big vacuum leak should show up on fuel trims though. Maybe you have a different problem. Probably worth checking to confirm before going crazy on solutions.

 

Thank y’all for the replies, I was keeping it on for awhile that hiss gets annoying quick lol! So I went to the junkyard today and got a switch out of an expedition, the tabs were broken off of the connector for the vacuum lines on the old switch I’m sure from when the previous owner put in the radio. No more leak! I don’t know how I missed those broken tabs, I must be more blind than I thought!