Run AC in Winter

Back to the original question, the electric AC compressor in the Prius is sealed like a home or appliance compressor. There is no external shaft seal to dry out and leak refrigerant on the Prius electric compressor, unlike a belt driven compressor on a conventional car. So a belt driven compressor in a conventional car does benefit by running it during the winter periodically to prevent the shaft seal from drying out and leaking refrigerant, but the sealed electric compressor in the Prius does not need to be run for that purpose.

 

Added XGauge for AC watts Ambient temp 13C, cabin temp set to 22C, set on Auto with AC on. The XGauge seemed to alternate, more or less equal times of 0, 200 and 250 (watts).
AC was on pretty much by necessity: 3 in the car, heavy rain.

 

That is what I have typically seen when using defrost mode in rainy weather during cooler periods. With this low wattage and compressor speed I have seen minimal impact on mpg.

 

I understand what you are saying and have read the Repair Manual searching for answers on the humidity sensor. Without the Toyota specs on the sensor and the AC amplifier, all we can go by is that one statement in the description.

Addendum: I just searched the Repair Manual for humidity. On page 5889 under a Communication Table chart it shows a communication between the Power Management Control ECU and the A/C Amplifier that lists a "Compressor humidity control start flag".

 

We did our typical downtown run last night, usual number of bodies, me driving, as usual. We did usual touch-and-go at destination, ie: keep the car on for the full trip. Ambient temp was 12C, actually very mild for this time of year.

The scangauge's always got one gauge showing accumulated mpg for the trip. Typically, without AC it'll be at or below 4.0 (liters per 100 km) by the time we get home. Last night, with steady AC use, it was 4.5. That's a decent 10% difference. To be fair it was a wet, crappy night.

 

I assume traffic was slow. The slower the trip, the larger the fraction of gas usage is for A/C.

• The slower moving the trip, the longer the A/C runs so the greater the gas use for A/C (assuming a/c is needed)
• The slower moving the trip, the lower the wind resistance and the lower the gas usage to move the car (at least for a Prius)

 

Traffic about the usual. Pretty light: weeknight between 9:30 and 11:30.

I'm always seeing similar AC impact. What this says to me is the prius AC may be high tech, but it's not farting rainbows, lol.

I'll continue to use it, but sparingly, 'cause I can see it impacting my mpg. Also it keeps the oil circulated (thread topic).

Another XGauge I've got on is BT2, monitoring middle sensor on hybrid battery. It was reading. 33C when we arrived home last night. That was with constant AC and ambient temp 12C. This is not any different than doing this runs other times without AC.

 

Just for ref: 4.0 liters/100 km converts to 59~ mpg, and 4.5 to 52. These are our trip outcomes without/with AC, similar conditions otherwise. We can't sustain those numbers for a tank, due to a lotta short trips. Have the 215/45R17 too.

 

If you just leave it on automatic, it will take care of itself.

 

Use your front windshield defroster when warming up the car, and your compressor will run.

 

Even just setting mode to heat/defog will activate AC. I was a little surprised by this, but have confirmed with my ScanGauge. You can verify fairly easy without instrumentation by running heat/defog mode (without AC button depressed), for say 15 minutes, in wet weather. Then switch to any other mode, and with a minute or two you'll get the humidity dump typical with turning AC off, and see the windshield quickly fog up.

 

When you need defogging in Vancouver you will generally need the a/c for defogging to work because the outdoor air generally contains too much moisture to quickly dry the windscreen.

The humidity dump is probably because its switching the a/c off before the moisture has time to drain so you go from defogging that's noisy because of the high fan speed to quiet operation with the reappearance of fog at least until things settle down. Its a bit of a nuisance and hopefully they will fix it in the Gen 4. I've been meaning to check if changing from ECO to Normal or Power modes helps.

 

i guess that solves the 'run a/c in the winter' problem.

 

The A/C is used to dehumidify the air in wintertime.

The compressor will run as needed to MAINTAIN PRESSURE in the A/C system. In the cold, it doesn't run as much as when it's hot and the A/C is really being tasked, but the system will run the cycle of pressurize and depressurize, so the compressor will kick in regularly.

Some cars tie the A/C function to the mode, do defrost automatically uses the compressor. If you have an A/C selector, you do have to remember to leave it on so that the compressor gets worked regularly.

 

An update:

I've been avoiding the heat/defog mode like the plague, based on my previous observations with Scangauge's XGauge ACw (Air Condition Watts, basically telling when the compressor is running, and how hard), that heat/defog was activating AC, regardless of the AC button being depressed (lit) or not.

But on an extended drive last night, with ambient temp reaching a high of +2C, the windshield was continuously on the edge of fogging, so caved and switched to heat/defog mode. After a bit I set one ScanGuage to ACw: it stayed on zero, never budged for the rest of the trip.

It's clear-and-cold, low humidity conditions right now. so not sure if it's some humidity sensor, or the low ambient temp, but it looks like AC will stay off with mode heat/defog, at least in these conditions.

 

I run the a/c whenever the relative humidity is high. That prevents fog on the inside of the windshield, especially if I adjust the mode so that there's air flow to the windshield as well as the footwells. I have never had any unusual noise because I have never needed to run the fan at greater than the "auto" speed.