I have a 1991 Cherokee, and my a/c blows ice cold. However, it will only blow through defrosters no matter what the controls are on (heat, a/c, vent, feet). I have changed out the controls in the dash and the vacuum booster canister thing behind the bumper on passenger side. It has plenty of vacuum at the canister. Thanks in advance for any input/help.

 

If you are positive that there are no vacuum leaks. You need to check the blend door to make sure that it isn't stuck.

 

Where's that? Behind dash?

 

It's been this way as long as I have owned it.

 

It is under the dash.

 

Do I have to pull the dash?

 

Doesn't the blend door just control from hot to cold?

 

Yes. Using a cable, not vacuum.

 

So what controls where the air blows from?

 

Vacuum is supplied to the heater controls from a reservoir behind the passenger's side front bumper. If the lines are broken or the res carcked, there will not be enough vacuum to operate the vent doors in the dash.

 

This ^^ You should also have 1 or 2 (cant remember) small red vacuum hoses on the passenger firewall under the hood. By the heater core area. Make sure these are hooked up too.

 

When I got the jeep the reservoir was cracked. I have replaced it, and when I pull the vacuum line off of it, it has plenty of vacuum. I also replaced the heat/ac controls in the cab under the radio. I just checked the 2 vacuum lines that come out of passenger firewall by heater core and they are both connected.

 

Here this might help you. Go to page 24-23

https://froehlichsuspension.3dcartst...mages/hvac.pdf

Did your canister have 1 or 2 vacuum lines? I know some of the older ones have 2. Trace those lines back. Search for abondoned lines around the battery, ect that someone might have left and just spliced or capped.

 

Canister has 1 line. Where do the lines by the heater core go inside cab?

 

And that link is awesome. Thanks.