90' Cherokee Loredo 4.0

My blower motor runs high and low intermittently...just sort of runs up high then drops lower..then back up... Also seems to have a delay in switching from vent to floor to defrost settings...seems like it wants to blow in defrost even when set to vent fairly regularly.

The AC needs a charge so not sure if it could be related. ?

I've searched and found about the same description (below) of my problem but the thread didn't go far enough to find the solution so....

Found many posts pointing to resistor if the motor on runs only on HIGH... mine will run at other speeds

Previous Post: Not mine
"when im cruising around town, 45-50mph, my a/c fan speed blows consistently. each speed blows properly. when i get on the freeway, the fan fluctuates. switch is on high but the blower will slow down for a minute, then speed up, etc. over and over till i exit freeway and slow down. it does the same thing in the winter with the heater on. it doesn't matter whether it's on recirculate, fresh or bi-level or what fan speed it's on.

is this the blower motor resistor?"

Reply said "check defrost vent" ?

Too new to know what that means specifically.

Any help/ideas very much appreciated!

Thx

 

When it fluctuates does it change areas the air is coming from. For instance does it change from the dash vents to the wind shield defrost vents. If so you have a vacuum leak some where.

 

Don't think so.....when the fan fluctuates in speed it doesn't appear to change where the air is coming from but I'll pay closer attention next time I drive it.

Thx

 

I pulled the vacuum line off my heater control valve when I did my cooling system rebuild and forgot to reconnect it when I was done. idling, steady cruise, and decel. I had dash air flow. Accel or hills it would go to defrost. Reconnected the line and now all is well. Check all your vac lines for leaks and the vac canister also.