Full Size Jeep Network

Can anyone give me some guidance on replacing the AC thermistor on the Evaporator? What is the best way to get to the evaporator? My thermistor appears to be bad after reading the resistance across it. Thanks!

although I have never replaced the FSJ thermistor,most of the ones I have replaced i.e. Toyota for example, you will have to discharge the refrigerent, drop the evap and remove hoses, split the case and there it is, usually the case needs to cleaned anyway, have fun

Exactly, and you cant split the case with it in the vehicle because the L bracket that mounts it to the dash covers up several of the fasteners that have to be removed to split the case.

sonoraed wrote: ↑Thu Feb 25, 2021 7:29 am although I have never replaced the FSJ thermistor,most of the ones I have replaced i.e. Toyota for example, you will have to discharge the refrigerent, drop the evap and remove hoses, split the case and there it is, usually the case needs to cleaned anyway, have fun

sonoraed wrote: ↑Thu Feb 25, 2021 7:29 am although I have never replaced the FSJ thermistor,most of the ones I have replaced i.e. Toyota for example, you will have to discharge the refrigerent, drop the evap and remove hoses, split the case and there it is, usually the case needs to cleaned anyway, have fun

When you say split the case you are referring to the "case" that all the vents are attached to?

Yes, the Case/Plenum houses all vents, fan/blower and the evaporator. There is a small access plate on the allow access to the control switches on the Pre-1984 units but it doesnt allow you to reach the Evap.

Yup the case has a upper/lower half, I wonder if parts are still available for the this version of FSJ AC controls, if not might go back to the separate blower switch and thermostat, parts for the older style are off the shelf aftermarket easy to obtain, Cheers.

The whole procedure is covered in some details in TSM. I haven't checked manual for your year, but 89 TSM has a 4-page description with a lot of pictures (starts at page 72 of Heating/AC chapter). According to TSM, it doesn't require discharging the system, but it requires a sketchy step of drilling a hole through AC housing which might go very wrong if you don't take precautions and drill goes too deep and penetrates the core.

I don't think there is any significant difference in regard to AC between 86 and 89 (I might be wrong), so hopefully that might help.

You can get a PDF of 89 TSM from Tom Collins site, here is a link (it is a big PDF, 300+ Mb)

FWIW, when I redid the AC on my 89, there was an access panel to the evaporator on the top of the housing, so no need to split the case. I had to remove some sticky moisture barrier stuff around the lines and top of the housing to gain access to the screws. From there, the evaporator can be removed. It's still tight though.

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Well duh ,had picture of early evaporator (switch’s in case) clearly shows removable cover plate


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Oh Man, I forgot about that! But there's no short cut, It all has to be pulled out from under the dash.

Agreed, most of the time there is a ton of debris and good cleaning is much needed, plus it's a good time to replace expansion valve, switch's,blower motor, parts are cheap and available.

An odd part to locate.....


Where specifically can I locate the replacement thermistor for 86 grand wagoneer? Thanks in advance