Prius AC blows hot only when outside > 77 F

Have a 2005 model, the AC cools very well if it is under about 77 degrees F. outside. Dealer techs have verified that it makes a great drop in temperature relative to ambient if the outside is cool.

Plenty of refrigerant at the right pressure according to them and the gauges all read normal when they see the car during the cool weather.

However, I have to deal with the AC when it is above 77 outside.

If it is warmer, the vents blow uncooled dry air from either outside or inside depending on the recirculation setting. I can hear the AC compressor whine, but it isn't doing anything to the temperature of the air coming through the vents at all.

The techs can't diagnose the problem because they only see the car on days when it is cold.

My hypothesis is that since the compressor works fine at low outside temps and there is plenty of refrigerant, there must be something unusual with the sensors feeding the AC ECU, the AC ECU, or the actuators that the ECU's drive.

I have a copy of the tech manual but there isn't a diagnostic fault tree for how to diagnose the compressor running but no cool air coming out of the vents due to other valve settings. I don't have a fancy OBD code reader...yet.

Thanks for any ideas,

 

Those are all good ideas, it will take me awhile to figure out where the lines/doors are and how I can observe them.

The questions I can answer easily are

I have tried all different combinations of manual with A/C on and off, automatic at regular temperatures and max-cold, and different combinations of recirculation on and off.

I am in Los Angeles CA with 147k miles on the prius. Outside weather was 96 deg F with about 17% humidity.

 

Is the only way to do this to use a Techstream and analyze the ultra-special OBD codes? I believe there are a set of button presses that goes into a mode where actuators are moved, but I don't know how to judge if a move was a success or a failure.

The metal tubing going into the sight glass is 98 F with the car off but the engine warm. If I turn the car on and the ICE runs for 30 seconds because there are 8 bars of charge, the metal tubing on the input to the sight glass becomes 111 F after running the A/C with no ICE for about 3 minutes. This is the tube coming out of the condenser going to expansion valve/evaporator.

This probably isn't useful information because I do not know the temperature of the tube going from the evaporator into the compressor because it is hidden inside the engine as near as I can tell.

At least one of the fans comes up to full bore the moment the A/C is clicked on based on sound. I can't see the side of the fans to judge whether more than one fan is running. I believe the fan(s) are as loud as they traditionally have been.

I did the force charging gag, with everything max-cold. With the ICE on, the temperature coming out of the vents is 0.8 deg F hotter than with the ICE off for a long time. This does not seem significant.

I changed the AC filter behind the glove box. It was clean. At 8 bars charge, the AC acts the same as if it was at 3 bars charge.

Thanks all,

 

I got into the actuator/sensor check mode that communicates through the MFD. The only DTC is 21; this is the solar sensor which I believe is quasi-normal. It was late afternoon.

I moved to actuator check step 2 which is where the compressor is at 7500 RPM (sounds like it too) and the air mix-damper is supposedly -10% or "cool". If I probe the suction hose between the evaporator and the compressor right around the "L" I get 101 degrees. If the bubble sight (the "H") is 111 degrees, that means there is some change in temperature either side of the condensor/compressor pair.

I did a more careful measurement of fresh air input temperature to vent temperature in the above state. The outside fresh air going in was 92 degrees and the air coming out of the vent was 84 degrees. The ICE was essentially off since the catalytic converter has stayed warm all afternoon. Eight degrees of temperature drop is something but not enough to deal with socal.

I still need to figure out a way to see the radiator fans visually and to double check the hot/cool mixing actuator.

 

I pulled the front grill and took some pictures of what I believe to be the front of the condenser:

Radiator_B by Docholo posted Nov 23, 2017 at 10:13 PM

Radiator_A by Docholo posted Nov 23, 2017 at 10:12 PM

I do not see a lot of biological debrie but it does look like the bottom half of the radiator has a lot of the fins folded over. I see that some people online try to to straighten these out, but it isn't clear if that actually works in practice.