97 TJ, 4.0, 3sp auto, no air
I have an odd heater issue. My heater heats just fine but I can only get air through the defroster vents OR the floor ducts; the heater control does noting regardless of the setting I put it on. When I turn the heat on it starts with defroster, for awhile, at some point I hear a loud Thump and my heated air is now coming through the botton ducts (the faster I run the motor the sooner this will happen). Turning everything off and starting again will just repeat the cycle.
I have removed and (visually) checked the heater controls and all seems okay and I am not sure where to go from here.
But if it's changing itself you'd think the problem would be under the dash, blend door perhaps?
Since it randomly changes itself, I'm leaning to it being a crack in the line at #8, not fully broken, just cracked.
The canister at number 8 is the vacuum reserve canister, its job is to maintain vacuum pressures to the hvac, cruise control while the engine load fluctuates, when there is a leak in the system it will cause erratic behaviors.
The faster the op runs the motor, the quicker they run out of vacuum pressure.
I see what you are saying, I read the first post and assumed when they said "the faster I run the motor the sooner this will happen" they were talking about the faster the idle in the engine, like driving under load.
If the thump comes from a faster running blower motor, then yeah you're right and should look into the blend door. blend door actuators.
Yea I get you there, I'm not sure what order the blend door travels but I know for a fact it starts on defrost everytime it starts from 0 vacuum. Defrost is default and if it moves from there then it's got some straight up dyson action going on.
Jeeps never get stuck or broke. Just parked in odd places for an indeterminate length of time.
Thanks for the info. To clarify the faster I run the heater motor the faster it "thumps" and changes. I will check the vacuum line especially the point indicated but in later posts it sounds like it may be the blend door actuators; if so, how do I check.