Deleted Coolant temperature switch (A/C) = issues?

[scheides]

A little history here, I have a 2G with a 6-bolt swap with a big FMIC and aluminum radiator that has overheating issues *ONLY* when the a/c is running for 10-15 minutes or more. Thermostat and all lines replaced last year.

Lately I noticed that when I have been accellerating/decelerating in traffic (full boost, then let off, stay in gear, then boost some more) my temp gauge drops way down and then back up to normal, as though there is an electrical short or something. The coolant is not low (making the sensor pick up air or anything), but there is a bit of oil residue on the sensors.

Now, I went to investigate this gauge-blipping issue today and I noticed that of the three tapped holes on/near my thermostat housing, two are present and connected (noted as labeled in the 1G haynes manual):
-Coolant temperature sending unit
-Coolant temperature sensor (ECM)

But there is simply a plug where the third unit should be:
-Coolant temperature switch (A/C)

So, what is this missing switch for and does "(A/C)" have something to do with air conditioning or some other term I'm failing to connect here? And because it is deleted, could it be causing these overheating issues? I can take pics if needed, but the sensor/switch that is missing is the one that threads directly into the thermostat housing, while the others thread in just below it.

[JET]

I am trying to remember, but I think that is kind of an overtemp safety thing. If the car gets too hot it shuts down the AC. I had it all figured out about 3 years ago, but I am a little fuzzy now.

[scheides]

Hrm, my car will do that. If it gets too hot, the a/c will turn off, and the air will blow straight outside temps until the temp sensor reads a more 'normal' temp. Then after a bit, the temp will rise again, and repeat. It's a viscious cycle! :)

[scheides]

C'mon, no one knows what this is for?

[Goat Blower]

It has nothing to do with your problem, but you can throw it in there if you still have AC, although I doubt if it integrates with your 2G wiring and ECU.

I used to know exactly what it did, but I don't remember and my cd drive isn't working. If you've got your DSM manual online(everybody should have this right next to their computer), each sensor is explained in the tech manual.

You might have a flaky temp sensor, the gauge one, not the ECU input. Or an actual restriction in your cooling system, or a bad radiator cap.

[scheides]

Where would something be clogging my cooling system? In the past year I've replaced the water pump, all radiator hoses, and even have a PWR aluminum radiator. I've replaced the thermostat (and I'm pretty sure the radiator cap at the same time), and still this problem persists (overheating). The jumpy temp gauge hasn't happened since I posted this, but the overheating thing is going to kill me in this heat!

[LightningGSX]

Maybe you're not getting enough airflow to remove heat from the radiator and the condenser at the same time.I would verify both fans come on at their high speed when the A/C is on.

[LightningGSX]

BTW The manual isn't really all that clear, but It looks like that sensor switches at 239 degrees, so I would assume it just de-clutches the A/C in case the engine overheats

[scheides]

Hrm, that seems to happen already though. Perhaps that's built into the 2g ecu, thus not needing it? Anyone else w/ a 2g have this switch on their t-stat housing?

Both fans do come on, (eric you wired them!) and I have a 2 SPAL high-flow fans: one 12" and one 10" but I do have a 3.5" thick FMIC core in front of them.

Does anyone else with a big, thick FMIC have overheating issues like this?

[A//// Guy]

Anyone with a FMIC should have much higher temps whent they use their AC. 2Gs have even worse airflow than my old 1G because the front end isnt as open either.

Even with my AC off my car used to get up to 220 or so on 90 degree days. So I couldnt use the ac on hot days anyway lol. I never did check to see if my headgasket was blown though. It didnt eat coolant and there was nothing in the oil so I imagine that wasnt the problem. I only had two 8 inch fans though....

Most dsmers with a FMIC dont have AC because they like to delete it.