rancur3p1c

I snipped this from the Air Conditioning section of the wiring diagrams in the repair info folder of the tech manual for my Scion tC. Pay attention the last bullet point-- "Rapid acceleration occurs"




Something that's bothered me since day 1 is the AC cycles when I'm accelerating, sapping power from the engine.

Any thoughts on why it's ignoring the acceleration state?

possibly related: engine load OBD2 PID "01 04" never exceeds 80% even with the pedal on the floor. I would think with the pedal to the floor it would be 100%...

rancur3p1c

well, since the day I bought it, the sub-par cooling performance has been because I was about 30% low on refrigerant. Having that topped up, cooling is much better, but I'm still going to modify the evaporator temperature sensor to run it a bit cooler-- currently coming out 39F, want as close to icing as I can get it. Anyone interested in a guide? I'll post about it anyways even if you guys aren't.

Now that refrigerant is where it should be, I think the compressor might not be cycling during acceleration, but I'm not sure. Will report back

simplytc

Would definitely be interested in a guide as the AC is never cold enough to me.

rancur3p1c

does is it get worse at stop lights?
by how much?

mc1114

I dont understand how people get very cold temperatures out of the vents. On a hot day with proper working A/C and refrigerant at the correct amount, every car I've owned (and there have been many) has had air out of the vents at mid to high 40s. Its gone into the lower 40s at highway speeds, but I've never seen high 30s on any car

rancur3p1c

Frankly, I don't believe what they told me at 39F either, so I bought some thermocouples to go with my multimeter and will be threading that down the vent to check myself. Once I know the exact temperature of the air and the exact temperature of the evaporator I will know how much lower I can drop the evaporator temp.

rancur3p1c

just jotting this down for later but note there is a service bulletin for the AC performance. Nominal spec from the factory service manual was 14.1oz +/- 1.1oz refrigerant (400g +/- 30g), people complained and service bulletin pushed this up to 15.2oz +/- 1.1oz.

The place I had mine serviced at said it was at 12, gave me 4 for 16oz total.

I would start with this. If you print up the service bulletin or just specifically tell the tech to make sure there's 16oz worth of r134a in the system and make sure they understand, that might help you a bit.

Poor performance right on startup is most likely because the pressure in the condenser gets let out. So, that condensed r134a that sits in the bottom of this picture in the "supercooling" portion has to be built up before the AC starts getting cold on a hot day. Having the correct amount of refrigerant available means the compressor readily has enough gaseous r134a to be able to build pressure to efficiently make condensed r134a.