UncleBob

I recently made a trip up north, and it got pretty freaking cold. I think it got down to around 3 degrees, which probably sent my old 1990 2nd Gen into shock. It sure did to me.

Since I got back, my AC has been INOP. The compressor clutch doesn't engage. This has got to be something simple, as my AC (old R12) was working flawlessly during the trip up.

Can cold kill a thermister? I've checked the fuses and circuit breaker. I also just found the link below on this site thanks to Corey.


http://www.pnw4runners.com/pdf/AC_HEATE.PDF

UncleBob

Okay, thanks to the link above, I decided to see if I could test out my Thermistor.

According to the directions in the link to test the Thermistor:

Trouble is, I'm not sure exactly what the Thermistor connector looks like. The pictures aren't the best. At my evaporator, on the driver's side, There is a 6-pin connector, screwed to the evaporator with a bracket, that has two opposing ends that are sandwiched between the evaporator halves. It has a Yellow/Green wire, and a Black/White one. Either the instructions above have a typo, (White/Black -vs- Black/White) or I'm not measuring the right pins. If I am measuring the right pins, I see an open, which would explain why my clutch isn't engaging.

Has anyone replaced their thermistor and can confirm I'm looking at the right connector? I'd hate to buy a new one only to find out I was Ohm-ing out my glove box door light.

EDIT:

According to the online FSM for a '93, the thermistor has different pins to measure. (What is WL in color code?). And my cooling unit evaporator doesn't look the same as the one in the '93 FSM.

http://personal.utulsa.edu/~nathan-b...20thermist.pdf

Are either of these directions correct?

This is on my 1990 2nd Gen, V6 Standard.

UncleBob

And, I found ANOTHER reference here of checking the thermistor, which says to OHM out a DIFFERENT set of pins.

So, I've found three different sets of intructions on which pins to check. Can anyone tell me which is correct for a 1990 4-Runner V6 Standard?

Is a Thermistor available at a FLAPS? Or do I have to go to the dealer? if it's available at the FLAPS, I'll just get one and check it at the counter.

Can a Mod move this to the electrical forum?

UncleBob

Update.

Called my local FLAPS and asked for a 'Thermistor'. The teenage mouth-breather said I must be talking about the 'Thermostat', and that yeah, they had one. I explained what a Thermistor does and where it goes. He suggested I purchase a PCV valve.

surf4runner

"evaporator thermistor is used to prevent evaporator from freezing up."

its a resistor that changes resistanse with temperature. it sounds like that would be the issue here.

for 4X4: it say the yel/grn with blk/wht
there is no polarity for resistance. and exact resistance is based on outside temp.

UncleBob

I realize there is no polarity for resistance, but blk/wht is NOT the same as wht/blk, therefore I had reason to question the instructions.

Also, the online FSM for 1993 wasn't correct either, in referring to my evaporator and pinouts for testing thermister.

Maybe my old 1990, since it was built in '89, used some leftover 1st generation parts? I dunno, but if you have a 1990 2nd Gen and run into the same issue as me, the thermistor plug IS the one that has 3 plugs, 2 of which are sandwiched in between both sides of your evaporator. Unscrew and unplug the main plug facing you. Since the driver side of the evaporator is the one that contains the thermister, test the two wires that go to that side. (The other side is a pressure switch..)

In my case, the thermistor were pins 1+2, which are Yellow/Green, and White/Blue.

Mine tested OK this evening, so my 'frozen thermistor' hypothesis was way off. I'm gonna take it in and have it checked by a pro.

UncleBob

Finally took it in. Wiring harness rubbed through an AC hose and dumped all that precious R12.

Replacing hose, dryer, and filling it back up with freon worth it's weight in gold. I like R12, though. It's important to me to see hard nipples when my AC is on LOW..