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Air Conditioning Efficiencies


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This is a general question -- applies to Caddies and everything else.

Is there enough of a gain in A/C efficiency to warrant using the "MAX A/C" or recirculate option almost all the time? Knowing that the A/C has to remove both heat and moisture from the air, it's understandable that recirculating relatively cool and dry air in the cabin would be more efficacious than using hot and steamy air from outside (especially "southeast" hot and steamy air). I know that on the AUTO setting, the car will often use the recirculate mode automatically, not even necessarily lighting the recirc button when it does it (so you never really know).

But would you save some compressor wear and tear (and fuel economy) by running the A/C in recirculate mode all the time...and just bumping the temperature up a little bit if it got too cool? Methinks it'd not really bring any measurable fuel economy comparisons, but it's food for thought anyway.

Jason(2001 STS, White Diamond)

"When you turn your car on...does it return the favor?"

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I dont think it would make any kind of noticable change, but my mom drives a Toyota Solara (pronounced Piece of Sh*t) and the ac in that thing is just not sized big enough. Even right after it is charged, it doesnt blow cold enough, untill you turn on recirc. It blows nice and cold once it is on recirc.

Ive noticed no change in the caddy... but it has alot more extra power to run ac than the toyota does.

Jonah

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Does the Cadillac cycle the compressor or blend warm air to maintain the set temperature?

I was thinking, that it blended warm air with the cold air to maintain your preset temp.

"IF" it does, then the compressor runs all time and it wouldn't make any difference in compressor wear, if it was on RECIRCULATE or not.

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I always laugh every winter. You see the Toyotas and Hondas with the 'recir' buttom left on. 4 people in the car and they cannot see out because of the fogged over windows..

For years, GM didnt have that button available. They only had a 'MAX' setting.

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Does the Cadillac cycle the compressor or blend warm air to maintain the set temperature?

I was thinking, that it blended warm air with the cold air to maintain your preset temp.

"IF" it does, then the compressor runs all time and it wouldn't make any difference in compressor wear, if it was on RECIRCULATE or not.

This is the key question, although I don't know the answer. I work as a diesel mechanic at a Mack truck

dealership, and on them, the compressor cycles on and off depending on the core temperature of the

evaporator via a themocouple. When A/C is in recirculate mode and the air in the cab cools, the compressor

clutch is disengaged about 50% of the time because it is pulling cooler air through the evaporator.

When in the fresh air mode it is always pulling hot outside air through the evaporator which is harder to cool,

and the compressor stays engaged about 85% of the time. ( We actually did this in the shop, and timed

the clutch cycles for a customer to show him the differance.)

Therefore, in this case running in recirculate mode actually saves compressor life and fuel, since the A/C

compressor robs the engine of horsepower.

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This is the key question, although I don't know the answer. I work as a diesel mechanic at a Mack truck

dealership, and on them, the compressor cycles on and off depending on the core temperature of the

evaporator via a themocouple. When A/C is in recirculate mode and the air in the cab cools, the compressor

clutch is disengaged about 50% of the time because it is pulling cooler air through the evaporator.

When in the fresh air mode it is always pulling hot outside air through the evaporator which is harder to cool,

and the compressor stays engaged about 85% of the time. ( We actually did this in the shop, and timed

the clutch cycles for a customer to show him the differance.)

Therefore, in this case running in recirculate mode actually saves compressor life and fuel, since the A/C

compressor robs the engine of horsepower.

Jerrymac, thanks for those numbers. That's exactly what I was looking for, and intuitively, it makes perfect sense. I can't believe that the Cadillac system would simply run the compressor at full duty cycle all the time, regardless of requested temperature. I could be wrong, but that does seem awfully inefficient.

Jason(2001 STS, White Diamond)

"When you turn your car on...does it return the favor?"

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This is the key question, although I don't know the answer. I work as a diesel mechanic at a Mack truck

dealership, and on them, the compressor cycles on and off depending on the core temperature of the

evaporator via a themocouple. When A/C is in recirculate mode and the air in the cab cools, the compressor

clutch is disengaged about 50% of the time because it is pulling cooler air through the evaporator.

When in the fresh air mode it is always pulling hot outside air through the evaporator which is harder to cool,

and the compressor stays engaged about 85% of the time. ( We actually did this in the shop, and timed

the clutch cycles for a customer to show him the differance.)

Therefore, in this case running in recirculate mode actually saves compressor life and fuel, since the A/C

compressor robs the engine of horsepower.

Jerrymac, thanks for those numbers. That's exactly what I was looking for, and intuitively, it makes perfect sense. I can't believe that the Cadillac system would simply run the compressor at full duty cycle all the time, regardless of requested temperature. I could be wrong, but that does seem awfully inefficient.

The compressor cycles according to the inputs from the temperature sensors in the lines near the evaporator. The compressor is very efficient compared to the old A-6 compressors from the '70s that used to run continuously (and could cool a reefer truck). I doubt that you would notice any measurable fuel economy gain by running the unit in recirc. mode.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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