[gabejeep]

Hi everybody,
Im trying to resolve some problems I'm having with my climate control in my 1997 Cherokee Sport XJ.

When you turn on the A/C or Heater none of the vents work. The heater works but the heat comes out of the floor area. The A/C doesn't work and none of the vents work either. If you turn the fan speed all the way up and switch the location of the vents on the controller, you can hear what sounds like a vaccum sound trying to switch the vents. However, no air comes out of the upper vents at all.

I was thinking that perhaps the A/C Heater Climate Control Unit is broken and this is why the vents are not working? However, I've heard that it could be the Rheostat and/or the fan relay or maybe a vaccum leak?

My question is: What should I do first to diagnose the problem?

Also, How do I check the Rheostat and or fan relay?

Thanks for the help guys!

-Topianno

[Reptile]

The control unit is the first thing to look at. Also, there should be a valve (can't think of it's name) that redirects the air flow between the vents, should be at the bottom of the dashboard passenger side. But it sounds like the control module in this case.

AC problems can be difficult to diagnose. You need a little patience and a voltmeter to test the circuits. I would test the module to see if all the settings work properly as far as current flowing thru it.

I don't think it's the fan relay or it would just won't run at all.

[AZ Jeff]

Your issue is probably vacuum related. Start by confirming you have vacuum on the inlet side of the heater control, Then test for vacuum on the outlet ports.

[gabejeep]

Hey Reptile,
Is there a way to diagnose whether the control unit is working properly or not? Ive been looking to buy a new one online but all the ones I've found are used units. I'd hate to buy a non working unit and not know it.

Thanks ahead of time!

-Topianno

[Reptile]

You can. Use a digital voltmeter in conductance tester mode and see if the current flows through the switch. But you'd probably need a wiring diagram to find out what color wire refers to, and test each switch function. For the temp switch, use it as an ohmeter to see if resistance changes gradually.

But the easiest way if you can is to go a junk yard. You might be lucky and find a replacement unit for very cheap. Not always guaranteed it will work, but worth the risk. You can also try ebay.

[AZ Jeff]

You guys are wasting your time testing electrical functions of the heater control. The direction of the air in the heater box is controlled by VACUUM. YOu need to get the vacuum diagram for the heater control system and start checking that out.

Check this diagram for help.