I have been trying to trouble shoot my wife's '99 Exp and things are getting worse as I go. It has had rough idle and missing on long hills. I was getting codes for LEAN Bank #1 and Bank #2 so I have been looking for a vacuum leak. During that process, I replaced the PCV valve. The aftermarket PCV valve was slightly shorter than the Ford part which caused it to pop out when I was driving. Then I really had a vacuum leak. The heater began to only put out hot air no matter what temperature I selected. I got the PCV valve reseated and temp control returned. Later, the PCV valve came out again and I again lost temperature control. I finally moved the heater hoses around enough that the PCV valve stays in place, but now the heater is staying hot no matter what temperature or which vents I select. Does anyone have a detailed diagram/description of the vacuum lines as they pertain to the heater system? Thanks.

 

The temperature is not controlled by vacuum. It used an electric actuator. Do you have the automatic or manual climate control?

 

Mine has "manual" controls and front and rear controls. Thanks.

 

Can you get the temp to change in the rear?

 

Follow the PCV hose around the back of the intake. There you will find an elbow where the line connects to the intake. This elbow is well know to fail and allow significant vacuum to escape.

 

Thanks, I already checked that connection. In fact, I have already had to replace that elbow...not a fun job.

 

Yes, it works fine in back.

 

First thing to check is the temp control ****. I had one crack and was no longer tight on the shaft. That did not allow me to adjust the temp. Just pull it off and look at the back side of it.