Anyone wanna tell me about this vac stuff...should i be able to blow air threw these hoses? the one hose that's for cruise and heater should i be able to push air in to it and it go threw freely or not at all?...im having one hell of a time getting my heat to stay the same temp all the time..ive replaced the thermostat...water pump...coolant temp sen...i just dont know anymore...some1 told me to check the vac hoses i did but im not sure if im doing it right or what i should be able to do or not do to them..Thanks ahead

 

If you hook up a vacuum gauge to your heater control/cruise control vacuum line to see if it holds a vacuum, then you shouldn't be able to blow air through it freely. If you can, there's a leak in the line, or it's disconnected at the other end.

 

I prefer a vac pump to check em, but you should not be able to blow air into this vac line because there is a check valve in it. The check valve is there so the engine doesnt deplete the vacuum supply under heavy accel, its there to keep the Cruise and A/C controls from changing with engine vacuum differences.

If you had a vacuum issue you would probably have issues with where the air is coming out and not with the temp (no vacuum would be stuck on DEF). The temp controls are electronic, with a little electric actuator that moves a temp door for hot/cold op.

 

Actually, at least in the case of my '91 Laredo, there is a Heater Water Control Valve that's mounted near the Passenger side of the fire wall. It's fed by engine coolant & is vacuum actuated. If the Vacuum Servo on the top of said valve has a vacuum leak i.e. cannot hold a vacuum for more than 5 minutes, then it will have to be replaced. Fortunately, this is a relatively simple process as you SHOULD be able to see it from the Passenger side of your Cherokee's engine compartment, next to the engine oil dipstick. You'll need to remove 2 screws (don't lose them, now!) as well as the vacuum line attachment to replace it, just as I had to do on mine to get fully functional heating on mine, at least temperature-wise. For making where the heat blows out from, that'll take more time & effort to get working, as you'll need to partially disassemble your dash to get at the Heater/Defroster Air Flow Control Door. Haynes & Chiltons Manuals, as well as the Factory Service Manual for your year, will be of great help & usefulness when doing this sort of work on your Heep. Hope this helps you...

 

yea I have the Haynes book, I will check that out thank you much