Prius A/C Cycle Question

You are right. It is the air conditioner cycling. It doesn't need to run all the time when it's not too hot out and if you don't have it set too low. Keep in mind that the fan speed is totally independent of what the AC is doing. In other words the fan will stay constant even thought the AC is cycling.

 

That's the genius design of Prius A/C. The compressor only runs at set temperature and stop when cabin temp. is right to the setting. Runs again when cabin temp. rises. Speed is control by computer. And on and off....... Never like conventional A/C,always runs at max cold and then use hot engine collent running around the coil to lower to the set temp.,if not set at max. cold. Wasting energy. Never match Prius design. Compressor of Prius last much longer. Enjoy.

 

I'm not sure if the compressor in the Prius is variable speed - but all auto systems cycle to maintain the evaporator temperature. Many of the newer systems have variable capacity systems that can actually vary output at the same RPM. The special thing about the ePrius is that it is electric -- so the engine does not need to be running. Modern auto AC systems are very efficient. I will admit the Prius compressor does have a strange sound.

 

Pretty much every hybrid nowadays has a variable speed compressor. Note that the Prius has an oddball "ejector cycle" A/C that needs a relatively high minimum speed to operate properly, hence the cycling at low load.

And while it's possible to build compressors that have variable capacity at one RPM (Copeland's Digital Scroll being the most notable), it's mostly obsolete since variable speed is so easy to implement nowadays. It's a lot cheaper to add in a motor control DSP than it is to implement a variable speed drive mechanically. Even cheap computer fans have variable speed motors nowadays.

 

I'm pretty sure the compressor is variable speed on my 2005.

- Alex

 

Setting with car in "ready" and the AC on, from the outside, the only thing I can hear cycling is the cooling fan blowing air across the condenser. Maybe the compressor is running at the same time, but I don't hear that.

 

I should have said variable output capacity at a given speed -- Many do not actually use the electric clutch unless they have a problem or you turn the system off -- the compressor is always on. I assumed that the capacity was controlled by the speed of the motor -- as in the inverter mini split systems.

 

Most A/C systems do cycle the compressor to vary the capacity, even almost all variable speed ones if the demand is low enough. The Copeland Digital Scroll as well as the (long obsolete) Brysch unloading compressor are designed to cycle much faster. The Digital Scroll uses hydraulics to separate the scrolls so they do no work, and the Brysch uses a solenoid to hold the suction valve open.

 

It sounds a little LOUD? unless you are in a vary quite place and have good ears. Yes some can have a little more noise then others. I have comes across a few 2010 that already needed a recharge, mostly taxis with over 150000 miles on them and had front end hit and a body shop ether did not replace a damaged condenser just straightened it and put it back in and it leaked later. The other is your insurance company told the body shop to use a cheaper part, not Toyota's. Some times they leak with in a year or it was never recharged correctly and you will hear this sound a little louder then normal. Pruis electric compressor do not like low or over charged refrigerant. It's death to them...

 

but on a 2012 may be normal. here in San Francisco its usually not that quiet to hear it. Did you buy your 2012 new ? or used? I have all ready came across a few that had front end damage and had the condenser replaced and after the A/C was recharged at a shop it would make noise. The new owners did not know, and ether the shop was still using and old air conditioning recharge that are not accurate for the small charge of the new cars and not be used on the newer cars of today.This is a vary big problem today, The EPA and the SAE have just passed new rules and laws about this problem. The only problem is that the shop owners do not want to spend $4000 to $6000 ++ for a new recycle & recharge machine.

 

Thanks Lech, lots of new interesting info on Prius AC in your posts. I looked at your photo gallery, too.
Dare to write a sticky for users on how to prolong the life of Prius AC and how to screen AC repairman before letting them to work on your car ?

Thanks,
- Alex