Hi! Thanks for your info. Did u plug it into the evaporator core? Do you think I can just connect a new probe to the existing 3 prong clip and have that work or would there be issues because the probe wasn't actually in the evaporator core?

 

S M R has not returned to this site in almost 4 years. Might want to try an e-mail. Left click on the screen name for the send an e-mail option.

 

Unless you at least locate it in the cold airflow, you run the risk of freezing up the evaporator with ice because the sensor cannot tell the pcm when the evaporator temp has dropped to near 32F. The early 4th gens cars used a compressor cycling design to prevent freeze-up and the pcm controls the compressor power. The freezing-up may not be damaging, as far as I know, but a real annoyance.

 

The factory manual indicates placement on the sensor in the evaporator is critical with regard to making good contact. It says not to use the same hole you pulled the old one out of, but to move away from the existing hole, and insert it in a new location on the condensate screen.

 

I'm not even sure if the issue with the AC is the evap temp sensor. I know I don't have power at the compressor because I jumped the relay and the compressor came on. It looks like the only things that can be causing the compressor to not come on would be the evap temp sensor, the refrigerant pressure switch, and also for some reason the coolant temp switch. Sorry if I didn't use the 100% correct terminology for those 3 sensors/switches, but I don't have the wiring diagram in front of me right now. I pulled the 3 prong connector for the evap temp sensor off yesterday and saw that it's kinda tight down there. I see that i will need to pull the heater core shield off at least and maybe the heater core to pull out the old evap temp sensor and insert a new one. For what it's worth, the ac stopped working 2 times over the past year, but came back within a day (intermittent problem). Now it is totally not coming on for a week. I know that my system is charged; I checked the pressure- it's good (like 150 psi/170 psi), so it's not low on refrigerant. What do ya'll recommend? i don't want to pull out the old evap temp switch if it's good. Any checks I can do? Like with my multi meter (checking volts or else) at the 3 prong connector where the evap temp sensor connects into that rectangular piece or somewhere else? Maybe just hot wiring the at that place would cause the compressor to come on- if that made the compressor come on, that would definitely tell me the evap temp sensor is bad. But, I'm not sure about a hot wire because there are 3 prongs which all go back to the PCM. It's not 1 + and 1 - and a ground. Recommendations!

 

Pull the pcm fuse for a few seconds, then check to see if the compressor will come on. If the pcm has disabled the compressor you have to reset the pcm before the compressor will work. Your pressure seems high to me. Those pressures aren't much below the high side pressure with the compressor running. I would scan the pcm. Check the Scan94/95 thread if you don't have a scanner. You can see what the evaporator temperature is, if the pcm is commanding the compressor on and what the high side pressure is. Scan94/95 also has an actuator function you can use to manually turn on the compressor. Seeing the scan data, and whether you can turn the compressor on with the actuator, may help you determine why your compressor isn't working.

I wouldn't replace the temperature probe unless I was positive it was the problem. According to the service manual you have to remove the heater core to get to the probe. It also says not to test the resistance because you may damage the probe.

 

When the indicated evaporator temp is below 36*F the PCM will disable the compressor clutch. With an open or shorted circuit, the PCM sets DTC 71. That code does NOT turn on the SES light. The factory manual does not specifically state that DTC 71 will or will not disable the compressor clutch.

The diagnostic chart for the code indicates that with the sensor disconnected from the harness, a Tech 1 should indicate 90*F. Yet on the other branch of the diagnostic chart, it indicates that a reading of 19* F may indicate an open circuit.

Confusing, because the evap temp sensor is not like any other on the car.... it is shown as a solid state thermistor, and should should not be probed to measure resistance, as this can damage the sensor.

 

So, the ac is working... But first- what is an obd 1 scan tool with running sensor data capabilities? Is this a special obd 1 scanner? I've been meaning to buy an obd 1 scanner. Also, I guess 9495 is a freeware? program written by a private party, like a dude yes? So, I plugged the evaporator sensor back in and turned the ac on max and there it worked. I really don't know if the issue is related to that as I had unplugged it and plugged it back in and turned the ac on with no good results yesterday. Today, somehow it worked. So, this is definetly an intermittent issue. It doesn't seem to be working 100 if that means anything. I don't think it ever worked better than that with me anyways. Its performance suffices in the hot central valley if that gives you an idea.

 

I just checked my pcm setup and the reading does go to 20F when the sensor voltage goes too high (5v). It goes to 90F when the voltage goes too low (0v). By the design of the sensor, an open circuit on the ground wire (makes the output ~5v, 20F) would have the opposite effect as an open circuit on the 5v wire (~0v output, 90F). When the output wire is open circuit, an internal pull-up resistor makes the voltage 5v (20F).

 

It was written by the member above who helped you in posts #18 and #24 (GaryDoug). Complete info on the free download is here:

https://www.camaroz28.com/forums/com...95-lt1-874306/

 

I am editing this comment. I mistyped an idea-
So, GaryDoug, I plan on downloading your program within the next few days. So, my ac has now gone out and back on afew times in the last few days. I guess the best course of action in this case is to scan with your scan9495 program while the ac is out? Also, last night as I was driving the car I opened the glovebox and there was no glovebox light. I was like oh, this car doesn't have a glovebox light, but then a light started to flicker on. It's intensity wavered for a minute before a constant intensity light illuminated the glove box. The ac hadn't been working prior to this (earlier in the day), but I was like, the ac will work now. I turned it on and it worked. Then I closed the glovebox and reopened it. The light never came back on. The ac continued to work, even after I turned the car off and turned it back on. I just thought this was alittle funny as the wiring for that light is in the same area as the wiring for the ac..
Regarding your previous comments, it seems that the way the sensor works is that it is very sensitive to temperature and at a relatively low temp, like 90F, the resistivity of the sensor becomes too high for current to pass through the sensor. At a low temp, like 20F, the resistivity is low and the current can pass through. So, when max current is flowing through the sensor, this causes the pcm to turn the compressor off. When no current is flowing, this causes the pcm to turn the compressor on. Interesting because it's alittle counterintuitive, from a basic series type model. Current through sensor, no current at compressor. no current through sensor, current at compressor (provided the ac is turned on and all other components are properly functioning). So yeah.... download and scan? Intermitent can be hard... plus working on this car is sooooo much harder than working on my 2001 Jeep Wrangler lol, but yeah- I'm down to investigate these things for sure. Open circuit issues like you were mentioning previously?????

 

Thank you very much for posting this information.
I have a 1997 Camaro SS and my mechanic says it needs to replace the Evap Temp Sensor but it is discontinue and can't find it.
I am assuming this is the same part as the one you describe here.
I am looking for it all over and can't find it even now that I have the part # from you.
I will keep looking...
Thanks!