In the morning on my way to work i drive with no A/C on (it's only 103 in the morning here in phoenix). But on my drive home it's been 115 or more and I have to use the A/C. Morning commutes = 55mpg, evening commutes = 45mpg. Does the a/c have one setting that is more efficient than the others? Any ideas/suggestions? Thanks!

 

Set 'Auto' mode, beginning at something barely tolerable like 90, then slowly creep down until you're comfortable. Recognize that the refrigerant in the system (134a, 22, 407c, whatever) combined with the limited condenser coil surface area will not be able to make it a chilly 70f no matter how hard it works in those kind of outside temperatures.

 

I've been using the auto, but I've had it set at 78, so I'll try setting it a bit higher.

 

Mine starts out at 78 or 79, in Auto, but I try to limit the fan to only 2 or 3 LEDs. Then I slowly lower the temp (if I feel the need) another few degrees.
It seems to make a difference, but my evening commute is often hotter as well, and my MPG is often a little lower (like 51 vs. 48). I'm usually more in a hurry in the morning, and relax a little more in the evening - otherwise my MPG difference would be more, I suspect.

 

It might not be the air conditioning. Do you live at a higher altitude than you work? That may be contributing to your good mileage going and poor mileage coming home. I used to get 60mpg going to our old office but only 40 coming home. The hills were pretty obvious though.

I used the air for the first time for any distance of drive today, but it was hard to quantify the effect. I had about 80 miles at 70mpg before my wife turned it on and we promptly fell to the 60s, but we also got off the interstate and into downtown Denver driving. Luckily, there was an afternoon storm that blew in so we were able to roll down the windows for the drive home.

 

I live in queen creek which has an elevation of 1400 and I work in scottsdale which is at 1200 feet. 200 feet of elevation shouldn't make that much difference, should it?

 

You might be surprised. I would guess that we live about 200 feet above and 10 miles away from the airport. When I drive there, I have gotten as high as 80mpg, and on the way home, as high as 55. It's the perfect glide there though where I have the valves closed much of the way. On the way home, I have to use gas.

I'm sure the gain/loss plays a role in your commute, as does the A/C. There are so many "gray" factors that effect FE. In my airport example, I am usually picking my wife up and leave with plenty of spare time. On the way home, she is usually looking forward to getting home so I probably drive a little faster.

 

Hi ryanw,

I looked up one of my old posts on this issue of elevation difference, and
found a good example of that effect in a short round trip of about 12 miles.

The inital downhill FE was my best ever 80mpg and the return home ended
with 63mpg for the round trip. This meant the return trip was 46mpg.

This is quite a difference due in part at least to difference in elevation.

The 80-85 degree F. temperature sure helped the initial leg, but could not
overcome the 250 foot rise on the way home.

These numbers show why I always maintain that only round trip mpg's are
significant as to the vehicle's and driver's performance (FE).

 

Yes, altitude differences can sure make a difference, if the commute is not very long.
The HCH2 gets into a real "groove" on level-to-slightly-downhill travel. You can easily hit 65-80 MPG for some stretches. And then there's the occasional EV mode, too (planned or not). These disappear if going *even slightly* uphill.

How long is your commute with this 200 ft elevation difference?

 

42 miles one way, all highway except the three miles from the freeway to my office.