ZJ defogging problem, wifey is unhappy

If you are talking about the inside of the windshield, you probably aren't getting any air conditioning with defrost for some reason. The A/C has to run to dehumidify the moist air. Of course the defroster will eventually do it with just max heat, but it's much faster with both heat and A/C.

Dick

Yes ment the inside of the windshield. A/C works on ac settings but I'm not sure if it is running on the defrost setting, is there a separate relay for the a/c when set to defrost?

Snow...

I went out and got my manual for the '93 ZJ. I am assuming you have the manual heat/air conditioning system. For maximum defrost (read that dehumidify in your case) put the selector knob in defrost (all the way to the right), heat full on, A/C on. It is important that you not have the temp control on full cool as that turns on the recirculation, and you want outside air, not inside when you are trying to defog the windows. Are you sure your air conditioning is working? Most '93's had a problem with the evaporator coil.

Dick

Yep a/c works, blows cold (had it topped up in July). I know the compressor will need to be changed as it has a bad internal vibration when the a/c runs (it also has that bad bearing sound when running). Thanks for the manual info (that's one thing that didn't come with the beast. The controls are that digital temp setting with the automatic fan and vent setting option (set then temp you want and the fan speeds and vents can be controlled and changed automatically).

Snow...

Anyone happen to know where I might find a pdf copy of the manual online?

I would first find the holes in the floor and fix them so the carpets will dry out. Wet carpets are usually the culprit for what you describe.

Then I would check if the AC was working because it is supposed to come on with the defrost to help dry things out.

Next I would make sure it isn't missing any coolant. A coolant leak in the heater core will cause foggy windows too.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Snow wrote:

OK, then your system has the Automatic Temperature Control like mine. To get maximum defrost, turn the middle knob to the defrost setting (first setting after auto.) Make sure A/C is ON. Look for the little star in the digital window. Make sure Recirc is OFF. The fan should go to high by itself. If it doesn't, turn the fan knob all the way to the right.

Dick

Dry carpet, no leaks (unlike my xj, but thats a different thing)

A/C works.

No coolant loss..

Thanks Mike Snow...

Ok I'll try that, think I get to drive the zj to work tonight (figures I get them when they have problems, I never get them for fun)

Snow...

Replace the heater core. It has a pinhole leak.

Earle

She could turn the AC on, and the fog would disappear like magic. Se the temp as desired, direct the air flow to the glass, and set the air conditioner on. Guaranteed to work every time.

Of course the AC works on the defrost setting.

Thanks Gents, I'll try some of these things on the way to work tonight. Think I need to ascertain first if the ac is actually turning on when set to defrost like it should.. We'll see what happens.

Snow...

"Like it should" is debatable. None of the cars that I currently own switch the AC on with the Defroster. The defroster is really just a selection of which vent holes you want the air to blow out of. Sure, some cars will switch the AC on if defrost is set, but this is not a requirement, and just because the AC does not come on by itself doesn't necessarily point to a problem. If you can set the defrost and turn the AC on at the same time, then you have what you were meant to have, or you have something that can work, and gives you options of where the air should blow from whether or not the AC is on.

This raises a point. Is this a new change in function?

Is there a misting of antifreeze on the windshield and smell from a pinhole leak in the heater core?

I thought all vehicles with AC automatically switched on the AC compressor when the defrost mode is selected. I thought that was standard for the last

20 or 30 years or so. All the GM, Ford, and Jeep vehicles that I have owned for the last 30 years have done that.

Tom

I can see where you might think that, but it isn't true. My BMW, Mazda MPV, and Toyota Tacoma -- I need to double check the Toyota -- do not automatically switch the AC on when the controls are set to Defrost. I prefer it this way, by the way.

If you think about it, you want to control the mode of operation and the air flow separately. You might WANT the air to come out of the defrost vents so that the hot air isn't in your face, so you would want to run the AC separately from the selection of defrost. You're right though, lots of cars take this selection away from us, and they switch the AC on whenever the Defrost is selected. I understand why they do this, but I like the ability to make my own choice. Technically, one can have the heater on -- no AC -- and have fogging problems, and setting the AC on in this case will solve the fogging without using the defrost. So, the defroster isn't the key to unfogging the windows, and setting the AC on just because the defroster is selected makes no sense if one pauses to ponder the issue.

Got to be a leaky heater core...

Earle

It isn't debatable on the ZJ, particularly with the ATC. Is noted in the owners and factory service manual as that is the way it works.

I honestly don't know of any modern car with A/C that doesn't turn on the AC with the defroster, but that doesn't mean you are totally incorrect.

Jeff Strickland proclaimed: