I have a 98.5 cummins 24v, the heater is stuck on defrost and it wont change? I checked the vacum hoses and they appear good. Any suggestions?

 

Its got to be one of two issues. Vacuum leak on one of the hoses or rubber elbows or a damaged blend door which controls airflow. The only way to really check for a leak is with a vacuum pump. Check the line starting at the nipple coming off the vacuum pump near the power steering pump and work back to the firewall. The rubber elbow on my 24valve was very brittle.

Good luck

 

I had this issue last fall. Mine was a vacuum leak on one of the lines that ran across my firewall.

 

thanks guys ill check it out

 

Joecool this might help

 

thanks i found it, was broke along firewall.