Good news! Swapped out the coolant temp sensor, no check engine light, no codes, FAN IS RUNNING!
Fan starts running above 210 far as I can tell.

OK! so that is done.

Now as for the AC - again, no code, I did see what the refrigerant refiller gage reads, and the needle goes to the red, so it's not low. it's basically indicating "technician service needed", should i stick in the new thermostat anyways?

Update: well, watching some guides on youtube, it's over pressure, i just released some pressure using the filler gage without a can attached, that fixed it for some, but not mine.
the AC fuse is popping immediately. I ruled out a faulty relay.
There is no CEL. What should I try?

 

You never told us the code.
If the compressor is not running it is useless to look at pressures.

 

You're making progress!

 

There is relief in ruling something out as I really don't know if it's trying to run or not. (but I see what you mean, if the fuse is blown it won't be running, still happy to potentially relieve too much pressure)
There's no code, unfortunately. after i replaced the coolant engine sensor, the CEL went away, and no codes are present using a code reader.
Here's a cool mystery: Before and after I replaced the part with my dad during a visit today, me and him both looked at his code reader show "none", and after the replacement he pressed the clear-code funtion, and the CEL went away.


Another consideration: since the fan is not kicking on til 210F+, i noticed after replacing the sensor, the temp digital dashboard readout behavior changed.
Before replacement: Idling, the temp would go to 230 relatively fast.
After replacement: we waited in his driveway for the temp to climb and the fan to kick on, but it would not go over 190, even in the middle of a hot 85 deg day. And it did not even break 200 driving an hour home until I started to go uphill into the mtns where I live. During that part of the drive it maxed out between 216-210, and finally, when I reached my gate and got out to unlock it did I hear (and visually check to see) the fan running, keeping it below 220 F.

So, it is lkely, the previous readings were unreliable and my engine never actually went into the red. Which is why it is stil alive, after hitting the maximum on the gage, visually.

It's a $7 part and a 10 min swap on an HHR, i wager it's a good idea to recommend this right away for this issue if the mileage is as high as mine, 150k, and they've never replaced it.

 

If the CEL is on there is a code. When you clear codes the CEL goes off, until the OBD test runs again. You should never clear codes, when the cause is fixed they go away, while they are there a technician cause them. The light is not the problem, turning it off doesn't help, especially if you need a smog test soon.
The sensor is a whole lot less likely than the t-stat to be the cause.
Why not let an expert look at your AC? If the compressor is not running why would you think the pressure readings would mean anything? The compressor makes the pressure.
The analog temp gauge on the dash is useless. Teats on a bull, like an ammeter.

P0128 is a test that looks at how long it takes for the coolant to get up to 180F from a cold start; if the ambient temperature is high it takes less time to get there if the engine is already warm it will get there quicker, that makes it intermittent. The usual cause is a t-stat stuck open, cheap ones have a rubber gasket that tends to dislodge and get stuck in the valve mechanism. If the P0128 is set the AC will not run and the digital temp will display "---", GMs way of telling you to stop ignoring the CEL.

Operating temperature is OVER 180, that is when the t-stat opens and stays open until the temp returns to 179F. The cooling fan turns on at about 219F and stays on until the t-stat closes. The exception being the fan runs if the AC compressor is running, either the button has been pushed or the defrost or recirc modes are on. The circulating blower must be on and the switch sending the on signal to the BCM for it to run.

The AC clutch has a fuse, a diode, a relay and the pressure switch. You can test the AC clutch by supplying 12V to the green re on the compressor (pin 87 on the relay) while the engine is running.

 

Noted will do!
to be clear, we checked for a code before i even touched the sensor. there was none, while the CEL was still on.
Then we replaced the sensor, checked again, and there still was no code, CEL still on. My dad hit 'clear'. He's the ex mechanic. :shrug:

 

some coder readers will not display codes from the transmission, or other areas that can rigger the CEL. I have an extremely cheap reader that doesn't show codes, I switch to my Autel scanner and it shows all the codes.

 

The only way the light can be on is if there is a code!! I does not have4 any other way to light up. Maybe you thought you could read them with the key off?

 

oh no not me, the car was turned on, again my dad did it with me sitting/watching, he has been doing mechanic stuff for his whole career.

but as the other user said, yea there is a possibility the code is coming from a place that reader can't detect, in which case, it'll probably turn back on eventually. We did read it a few weeks back actually, and a code did come up, it said something about coolant temp fault. and he cleared it, but it resurfaced. cars are not immune to glitching either, though i figure that is quite rare.

 

Next time, before your Dad clears any codes , write down the number, then post the numbers here .