Recorded some data. My house thermometer said it was 99 outside, despite starting this after 8pm. I set the sensor on top of my winch so I would get a good reading of what was actually coming in to the radiator. There was definitely some recirculation of air coming from under the engine compartment and back around. It felt a lot nicer not standing right in front of it.
1. I started logging while idling with the AC off. After 7 or 8 minutes, the ECT had stabilized at about 192.
2. At that point I turned the AC on full fan speed and recirc. You see that as the first blip in the rpm curve where idle jumped from ~650 to ~720. Running half doors with no windows so AC was not getting the benefit of preconditioned intake air. Temp eventually seemed to stabilize at 223.
3. Hand throttled as little as I possibly good to idle up. I didn't notice until I looked at the graph but it was bumping up and down between ~1240 and ~1310. Maybe the extra compressor speed was pulling the suction down enough to cycle the compressor? I didn't hear it, but I was also organizing tools in my garage to kill the time. ECT eventually stabilized at 199.
4. Released hand throttle and turned off AC, opened the hood and started poking around with my IR thermometer. Looks like there was an initial small climb to 203 and then it started falling again before I shut it off. You can definitely see the impact of the AC condenser on the underhood air, in the IAT reading.
Other Temperature measurements
AC system
With AC on and normal idle speed I was getting 52° out of the dash vents and a little bit out of the floor at about 70-75°. Condenser was reading 160 in the upper passenger, 150 on the upper and lower driver, and 145 in the lower passenger. I suspect the saturated condensing temp to be in the 150 neighborhood, with the first and last sections performing some desuperheating and subcooling, respectively. 150 corresponds to a pressure of 263 at the condenser, and there's probably a few pounds of pressure drop in the lines and the desuperheating section of the condenser, so that probably puts it in the lower end of the range for 100F ambient.
Cooling system
The IR gun seemed seemed to agree with the ECT sensor so I can probably rule out an erroneously high temp reading (as well as the fact that it stabilized at 192 with no AC which would imply it was being set by the 195 thermostat at that point). IR gun read about 18 degree temperature drop from the radiator inlet to the outlet with the hood open/normal idle/AC off. I have no idea what's normal/expected there. I had visually verified the orientation of the fan but just for fun I put a shred of plastic shopping sack on the end of a pick to serve as an indicator flag, and made sure it was pulling air INTO the radiator and not blowing out of it.
When I shut it down I immediately attempted to move the fan clutch (factory with 130k miles and 16 years of service) and it's just as easy to turn as it is when it's been sitting off overnight, which is also much easier to turn than the brand new Hayden 2791 sitting on my desk. I don't know if that actually tells me anything because I haven't studied the mechanical workings of a viscous fan clutch to even know whether it has to be spinning for the lockup effect to work. Even the FSM is pretty vague on testing a fan clutch...basically you stick a temp probe in front of it, block the radiator and run it and see if it speeds up between 165-185, then remove the radiator block and see if it slows down again somewhere between 180 and 135. By the time you do all that for an "it's at least somewhat working", you could have replaced it.
I plan to repeat this after I replace my factory fan clutch.
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