Gevo

AC system started acting up
My diagnosis shows that the AC cut off relay is not making contact when system is turned on. It was difficult to find the wiring diagram, but even with the wiring diagram nowhere does it mention If that relay is normally open or closed. In fact in the fsm wiring diag for 1993 model it shows open, other one I found shows closed. basically I need to know if the temp switch is supposed to swich it open or closed during normal operation.

Gevo

Here is a wiring diagram I found. See last page. http://www.pnw4runners.com/pdf/AC_HEATE.PDF

RJR

The cutoff relay has to be closed for normal operation to supply power to the AC amplifier and thus to the compressor clutch.

Gevo

Ok, so far so good. So, the way I am interpreting the system is that the Temp sensor/switch should be OPEN for the Relay to be closed, correct? So, let's say the temp switch was not plugged in, the cut off relay would NOT switch to close the circuit, right? SO the temp switch contacts ground to complete the circuit to close the cut off relay? Or, is it the opposite? This information is not clear in any of the literature I've seen.

I am trying not to change the temp sensor/switch until I conclusively diagnose it.

RJR

Kind of looks that way on the wiring diagram, but according to the FSM troubleshooting guide for the cutoff relay, the relay closes when 12V is applies across the relay coil (pins 1 and 3). So, the temp sensor switch would have to be CLOSED for the relay to be closed.

Gevo

Ok, great.
So, I will check the Pink wire across a 12 volt source. I should see voltage for normal operation. And then I will check the input voltage on the relay across a good known ground (I have checked this part already and it was good)

Will report!

Thanks Ron.

Gevo

I was planning on checking the system as I posted earlier. Yesterday, before I had checked it out, the relay started to click on and off sporadically. I had been jumpering the clutch straight up for AC until I fixed this issue. I unplugged the relay, and checked it out today.

Well, as we thought Ron, the normal operation IS when the pink wire (temp switch) is grounding. I plugged everything in as it should be, un-hoked the jumper to the clutch and it was working perfectly. I checked wires for looseness, shook the harness a bit etc... everything was good. I have no idea what was causing the issue before. Regardless I unplugged the wire at the temp switch, cleaned the contacts and plugged it back in.

Anyway, it was all pointless but it works now and I hope it stays that way.

I just wanted to post to confirm that our initial idea about the cut off relay circuit was correct.

cheers!

RJR

Thanks. Always good to get verification of theories. I'm glad it's working now; I hope it continues. Sounds like you might have had a dirty connection where the relay plugs in, or something.

Gevo

Back.

I am intermittently getting this issue again. I turn the AC on and off a few times and it works. I tested the relay, it's working perfectly. I'm assuming it's the temp switch.

Problem is, I can not find the part number! I just searched for a while, and I dont see it. I checked in the A/C diagrams, the coolant diagrams, the relay and switch diagrams.. etc.. I searched on google for part number as well.

Anyone can point me in the right direction would be great help!

Thanks.

scope103

Could it be Thermistor, Cooler No. 1 ? http://www.toyotapartsoverstock.com/...modelYear=1991

Did you try the test procedure?

Gevo

Im pretty sure its not anything related to the thermistor. It plugged into the bypass coolant manifold with 4 other heat sensors.

The prpblem is that its intermittant. The few times that it acts up im not in a position to test anything, when I can test its working.

Once, on my street bike, took me nearly year to find an intermittent headlight problem. Solder had come loose. :/

wyoming9

iTrader: (1)

Pretty much any temp sensor is a thermistor as the temperature changes the resistance changes Toyota call these parts strange at times..

Looking at the EWD it is indeed a switch

Gevo

Interesting, thanks for that education wyoming.

However, I am sure that it is not the 'thermistor, cooler No. 1" in the diagram Scope shared. That one is on the inside of the car. Although it is also connected to the cut off relay.
As I wrote that I realized Scope may have meant that my problem can be the thermistor instead of temp switch...? I'm pretty sure it's the temp switch, if I remember correctly the first time around it was acting up, the circuit of the temp switch was the only one not acting as it should (pink wire continuity to ground).

Gevo

I almost found one
http://www.summitracing.com/parts/sm.../model/4runner

Getting closer....

Gevo

I'm not going to trust auto parts websites....?
http://www.oreillyauto.com/site/c/se...ner&vi=1272361

scope103

Are you referring to the "engine coolant temp switch" shown as #12 here ? Which means you have 4wd and Automatic.

I don't think this will help much, as it seems to show the sensor configuration for the Manual (or 2wd) without that sensor.

But, you could "test" it after a fashion by just connecting the lead to ground. That would tell the cut off relay that the engine temperature is always "low enough." If your problem goes away, you'd have a clue. (note that a loose connection would trigger the cutoff relay, which is more likely than a bad sensor.)

Gevo

Yes Scope, I am waiting for it to act up again and I will pop the hood and wiggle the connector and see what happens. I tested the temp switch when the engine was off months ago, cleaned it up and made sure it was working. I jut remembered this part, lol.
And with the electrical track record of this car, I wouldn't be surprised ...

wyoming9

iTrader: (1)

So your saying the switch is good it might be the wiring including connections or the cut out relay itself??

As the switch when closed allows the coil circuit to complete

Now looking at the 92 4Ruuner EWD the switch is in the closed position at low coolant temps this keeps the coil on the AC cut relay energized holding the contacts closed.

When the coolant temp raises to the point the switch opens the coil drops out the cut relay opens.

Now if the way things are drawn in the EWD is a misprint who can say

Gevo

Wyoming,
I am agreeing with scope that the wiring/connector is more likely the problem than the switch. It's just difficult to determine when the problem is intermittent, I'll eventually figure it out. Meanwhile my goal was to just change the temp switch anyway to rule it out conclusively since it was a few bucks, but the problem started when I couldn't locate a replacement.

Earlier in the thread a discussion with RJR and others show that I agree with your description of the switches operation.

scope103

Think about wiring a "12v" LED http://www.radioshack.com/product/in...tent=CT2032233 (these have an integral resistor; you can put one together yourself for much less money, but why bother) between 12v and the temperature sensor. The light should be on all the time; if it goes off check the AC. Better yet, hook the sensor end of the light to the wire (not the sensor), and it will also detect a "bad connection."