I have a 1988 jeep cherokee.... if im not getting suction from the heater control valve...... where could the problem lie?

should connect to the top

hi there.
check this link out might show you.
Where is the heater water control valve on 94 Grand Cherokee Limited...

check your coolant level and check for hoses.

The valve that controls the water through the heater is not operating fully or the heater core is getting blocked.There is 2 hoses that go through the firewall to the heater core.If you look at the heater valve whilst someone operates it from inside the car,and you look in the engine bay,make sure the valve is working.Put your hands on the hoses and you can feel the hot water going through.(or not)Use this as a starting point and you may work out what is wrong.Hope this helps

Make sure there is vacuum going to the heater box servo motors and the temp control. If you have a good vac signal then either the servo has failed or a plenum door is stuck. If there is no vacuum then check at the control and at the engine and trace to find reason.

If line is really old, remove it and replace it. If you don't need to replace the entire length, put a short piece of small diameter steel brake line or other tubing in line where you wish to splice it. You can likely find a coupler made by a company called "help". Easy job!!

U need to replace the blower motor speed control resistor.

your control valve is in the dash assembly, passenger side. buried. its not in the engine compartment. im having the same problem with mine...i am thinking its more like the climate control is screwed up.

Go to engine compartment, locate heater control valve. It will have the heater hoses connected to it that pass into the firewall. Unhook actuation plunger on the control valve. This will allow the coolant to flow though the heater core at all times. Now you have heat. If you get too hot, you can control it by the hot/cold settings to adjust the heater door.

Pcv valve is normally on the valve cover.