The only issue I ran into when briefly considering an alternate, is the thermistor sends a resistance value to that little control box, then of course routes the signal/reference voltage to the PCM which opens or closes the ground for the AC clutch relay.

Of course, the resistance converted to an SV for the PCM based on the temperature changes the probe picks up is the question I ran into and haven't researched further. I'm not sure if it's a 1V-5V VDC that is the range output to the PCM or what. Will require some more digging, but I'd almost bet a similar probe (length) on other vehicles that are still available on the market would work. The specs of course would have to be compared to the function of the OEM thermistor.

I have a gentleman that has a few he's parting out, 2 that he pulled were cracked right after the probe passes through the airbox (years of vibes most likely) and should've been installed with a grommet or RTV. Awful GM engineering.




Images he sent me. Still functional? Probably. But I'm hoping for a whole one.

-Eric

 

Something like this has to be a similar spec range. How far off could the resistance values be? Haha

Really need datasheets.

 

Sorry I have not been able to spend more time with this. I think the only real requirement that the sensor outputs the same voltage as the original at 32F. The goal is to stop the compressor if the temp is near freezing so the evaporator does not fill with ice and block airflow.

 

Oh no worries, I'm definitely in no hurry and I'm digging into it when I'm on days off. It's that control box that I'm curious about. Wiring in a replacement thermistor (like you were saying a sub or alternate) wouldn't be difficult, as long as it sends the proper voltages to the PCM for AC clutch relay operation I'm golden. I have to get one of those boxes first so I can play with it.

 

Gary: any idea what’s in “the control box”?

 

I am pretty sure it is a solid state buffer device that reads the sensor and outputs a dc voltage of low impedance and filtering to make it good enough to avoid electrical interference.
I know what works for my benchtop PCM setup but that is not likely the best approach in the real world. "Occams razor" solutions don't usually work well in electronics ;-)
I wish I had a real car to try it on. Should have bought yours!

 

I have 2 of them (used) that should be shipped out to me today, and not this weekend but the next I'll be on days off and investigate further once I have them on my bench. If another sensor can be soldered/spliced in on the cable that goes back the the box, and still provide the same form, fit, function, we may end up having a long term solution for when one breaks/stops working.

 

I'm feeling kinda dumb because I'm struggling to find the wire gage sizes for the various runs in the engine bay. I've got several simplified schematics I've found in the factory service manual, but they don't show gage size. I can spec them via Amp draw, but it'd be nice to find it in the reference.

 

The factory wiring diagrams show wire gage, but they are in metric units (square millimeters).

In the 94 factory service manual, look at page 8A-3-1 for the key to wiring diagram labels. Note that "Wire gage and insulation color are labeled". Wire gage and insulation color is typically on the left side of the wire, opposite the 3-digit circuit number to the right side. The example shown is ".5 RED".

.5 metric = 20ga AWG. You need to reference a Metric to AWG conversion chart.

Here's one:

https://www.lapptannehill.com/resour...nversion-chart

 

Ahhh, that's what I needed! You rock Fred, thank you. Making notes now.

 

Mechanical engineer beats the EE to the punch again...wtg! Fred, you are apparently getting smarted, not older.

 

I hesitate to ask this but maybe you could send one to me. I did serve a year being a component failure analysis engineer and may be able to open some doors. I would of course send it back if I can't help and would do no invasive work to compromise it.

 

I just got them in, and going to check them out tomorrow. I can send you one if you like. I'm planning on performing resistance tests and changing the temp of the probe with water.

I've got the schematics and making a wiring list of everything I'll be ordering from EFI.

I was curious if there is a place in the factory service manual that has a list of the different splice points and where they live in the engine bay. I see various splices that I'm making reference notes to, but was looking for more info.

 

The electrical section is broken down into various systems. The section for AC control should have the schematic, and following that a list of all splices, pass throughs, sensors, etc. That component list will also tell you where to find the harness routing diagrams for the component. I think the routing diagrams are in section 200 or 201, something like that.

 

Fred is right of course. Since the sensor cable is in the passenger compartment, look there first of course. The PCM is just ahead of that area through the firewall so the wires should be short and may not be very accessible.