Weak A/C when it is hot

There are a few possibilities-

Your Mazda anecdote is sort of plausible- in the Prius the little doors that control hot and cold air blending are driven by small electric motors, and they can break, stick or stall. The system does have a diagnostic mode, but I don't know how to access it.

Also be aware that the ECU can unilaterally decide to cut back on air conditioning if it thinks the engine or inverter is close to overheating, thus preserving cooling performance in a last-ditch effort to forestall a real overheat. The car doesn't have a temp gauge, so you wouldn't know that this is playing out in the background. You can add a gauge or set up a diagnostic computer or use a phone app to monitor water temps if you suspect this.

 

So Calif saw its first hot day in a while? You have been driving in Southern Calif with the ac off?

Sometimes when the hybrid battery fails it will shut the ac compressor off to preserve its life.

Have you ever heard a loud fan noise in the backseat? That's the hybrid cooling fan the hybrid battery starts to die it will turn that fan on full blast. if you let the car sit in the sun all day it will come on too. Your literally cooking the battery to death doing that.

You will have alot of ac issues if you let the car sit in the sun all day with no windshield shade. Huge windshield for a little car.The car will reach incredibly hot temps that will take the ac a long time to dissipate. You must keep the cabin as cool as you can unless you want to be
buying a new hybrid battery.

Btw, what did the dealer charge you to replace the combo meter the speedometer meter?

 

Highly unlikely replacement of the Combo Meter (Combination Meter: spedometer/odometer/tripmeter/gear indicator) resulted in the AC being inopperable. The dealer (assumed Toyota) would have had to disconnect the MFD (Multifunction Display): MPG, Hybrid Batter, Energy flow indicator, HVAC, Radio dispaly. You would have absolutely noticed a non-working MFD.

It could be a bad inverter pump. But, that would have produced a warning light. OP can EASILY check the functional status of the inverter pump.

1) open engine hood.
2) make car IG-ON (foot OFF Brake) press START button twice. OR just make car READY (keep BRAKE pedal depressed, press START).
3) Open inverter coolant reservoir (the off white container) between the air filter and the inverter (big silver square w/ Toyota emblem and "Hybrid Synergy Drive")
4) Do you see fluid movement? It flows at a rate of a gentle stream; some call it "turbulence," but I feel that is a horrible description; to me turbulence = white water rapids, which the inverter pump does NOT produce. Flash light might help to see. If the area you are checking is quiet, you will hear what sounds like an aquarium pump. If you put your hand on the inverter coolant reservoir (the white opaque container), you might feel vibration (assuming engine is not running). NO FLUID MOVEMENT = dead inverter pump. REPLACE IMMEDIATELY!​

HV Battery could be bad, but that would produce other tell tale signs/symptoms. Dash lights. Hearing HV fan in back. ...

Absence of a bad inverter pump, I put my money on a leak in the AC system. This is easily verified w/ an AC manifold gauge set. Few shops are able to work on the Prius AC system, competently.

Consider putting your actual location (home or work) instead of "Southern California". If you are concerned about privacy; lie and put a neighboring city if that will make you feel better. BTW, privacy does NOT exist! Big tech (FakeBook , Google, etc) selling your info to any/everyone. Experian data breech of 143million Americans (just under 1/2 of US population of approx 327million). All the other data breeches: Target, Home Depot, Orbitz, Marriot, LabQuest, LabCorp, and the many non-reported breeches. The criminals have your information (a little to a lot of it). If you used LinkedIn, you have been voluntarily giving out a lot of valuable info for the criminals to see.

Given your screen name of "pasadena_comm"(ute), you live/work in "metropolitan" Los Angeles. Just contact member @Avi's Advanced Automotive. He has a shop near USC; competent and reputable, so you would be in very good hands.
Hybrid Fix - 65 Reviews - Auto Repair - 3790 S Western Ave, Exposition Park, Los Angeles, CA - Phone Number - Yelp

Let us know what turns up.

 

Don't hold the 12V battery against the Prius. A conventional car would burn through far more 12V batteries. Don't let any 12V battery experience a severe discharge event, to maximize its longevity. The longest I have heard of someone on the original 12V battery was 10years!

Any car kept long enough (years/miles), parts will unfortunately wear out. Combo meter (bad design/capacitors) and AC aren't exempt. Unfortunately you are on the receiving end of these repairs since the car is 12years old. The earlier owner(s) would probably report very little trouble due to the car being young/low miles.

 

If anyone asks, you never heard this from me, but it's covered in the repair manual. Starts with holding the AUTO and RECIRC buttons down while powering the car on.

Lets you get a lot of information even more easily than digging down for possible bad connections.

Speaking of connectors, pretty much all of them all over the car have latching mechanisms. The chance of one being not plugged in correctly is pretty low, unless it's been that way ever since the factory, or you have some knowledge of recent work in that area.

 

So this is the first time you mentioned poor gas mileage. What mileage are you currently getting?

 

Actually, a bad 12V is a very common cause of poor gas mileage in the Prius because it does so little work you don't know it's bad till it quits all together.

As for the A/C, I would go the obvious route and check the freon first. That's the most usual cause of warm air coming out of it. And it will also kill your gas mileage. Make sure whoever checks the pressure uses gauges for hybrid car A/Cs. The oil from a regular A/C will damage your compressor.

 

Veering off topic? How would a person that never saw that thread know about it? Plus the problem could be linked. Best of luck.

 

Not all 12y/o cars need a recharge. My 2007 still blows cold and the HI and Low side are w/in specs; never recharged either.

RULE OUT LEAKS! Otherwise you will be in the same position.

Remember, the AC system is a closed system. What does that mean? A closed system by definition is closed: nothing in or out. However, in the real world, the automotive AC system can loose small amounts of refrigerant over time due to leaks (via seals), or massive amounts of refrigerant due to equipment failure, road debris damaging AC components, or vehicle accident(s).

 

How much did the dealership charge for vacuum and refill?

I changed my AC fan last year. It was working on and off towards the end but when the car was moving I was getting some air. Luckily, the part is fairly cheap and the work as easy as changing the cabin filter. Just a couple of screws and a plug. Maybe 30 min.

I also added some refrigerant with a cheap refilling kit and waiting to see if I have a slow leak. Two weeks now still cold.