Heater Problem

Have a '96 Jeep Cherokee Sport, 4.0. Have had this problem for a few years now and troubleshooting is driving me crazy. Whenever the heater or A/C system is operating the blower direction switches to the defrost duct under acceleration. Also have situation where air comes in on passenger side no matter wehere the heater control is set.

Any suggestions?????

I think it is a vaccum problem...like maybe a hose being disconnected or loose.

http://www.dua1.com/AdminFiles/Jeep/93/HEATER_Core.pdf

See if the diagram at the bottom will help.

Yup, underdash vent direction is controlled by vacuum; under acceleration the amount of vacuum changes.

Thanks guys.

I started my troubleshooting at the heater control unit. After removing it I saw that the blower switch wiring connection was pretty burned and melted and the switch connecting prongs were in bad shape too. I took a trip to my local salvage yard in search of a control unit. I had to pull three units until I found one that didn't have the same condtions as mine. I cut the wiring on that harness so I could keep the good connector. The cost was $35.00 beating the retail cost of $101.00 at my local dealership. Came home, spliced the new harness into the old wiiring, and reinstalled the replacement control unit. PROBLEMS SOLVED !!! Apparently I had a bad control unit or the vacum cluster connection to the unit wasn't seated correctly. Either way, my wife is a happy person to have here Jeep's heating/cooling system working correctly, something it has never done since she bought it in 1998.

Thanks again for the help. Put the control unit in the memory banks if anyone else has this problem too.

Your are right...melted switches are also a common problem with the heater control.