heater and ac not working

[hugeredford]

I have a 1999 sd 350 and last summer the ac quit working and now that it is getting colder I noticed that my heat and defrost doesn't work but the fan blows at all speeds and different positions is this a common problem with the trucks

 

[DaveBen]

You have a vacumm leak. Look on the firewall near the A/C unit at all of the vacumm hoses. Your truck is old enough that the hoses need to be replaced. It will work the instant you find and replace the one that is leaking.

Dave

 

[hugeredford]

But is that why the ac clutch won't kick in or is all of that controlled by on switch

 

[fordtrucker4life!]

the clutch wont engage and it wont blow cold if it is low on freon but the fan will turn on, i dont know about the switch though