random A/C question
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Member
Joined: Feb 2001
Posts: 58
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From: Geneva, IL.
random A/C question
I recently read a review on a car, and it stated that the A/C automatically comes on when running the defroster. I have now noticed that the A/C runs in my truck when it is in MAX, NORM, PANEL & FLOOR, DEF, and DEF & FLOOR. The reason I found all this out was because of that article, and it got me thinking. Why do automakers do that? I know that the window will defrost better with dry air, but in the winter the outside air is normally pretty dry anyway. So does that mean that all this winter I have been driving around in DEF & FLOOR, and have been running the A/C with the temp on hot? Does the A/C kick off after the temp is turned to the hot position? If so, where is the cutoff point? If not, doesn't this put more wear and tear on my A/C unit? Would this contribute to my already dismal MPG showing in the winter?
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'98 SC XLT 4.2
4x2 3.55 ls
Gibson 3" cat back
K&N filter (who doesn't?)
Cpt. chairs, and those oh so cool auto headlights.
Factory door steps to get my pants dirty
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'01 VW Jetta TDI
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'98 SC XLT 4.2
4x2 3.55 ls
Gibson 3" cat back
K&N filter (who doesn't?)
Cpt. chairs, and those oh so cool auto headlights.
Factory door steps to get my pants dirty
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'01 VW Jetta TDI
Senior Member
Joined: Jan 2000
Posts: 3,205
Likes: 3
From: Along Lake Erie
OK, the answers are Yes, no, no, yes, yes.
The theory behind running the AC is just as you said: To dry the humidity out of the air. On most vehicles, the AC compressor will not cycle when it's below 45-50 degrees because, as you said, the air is already pretty dry at that point. I know in my Probe it cycles until it's around 35 degrees out, but it just varies from car to car. Does it put additional wear and tear on it? Yes, but it's marginal. Does it hurt the mileage? Minimally, but yes, in theory, it does. In our trucks, however, it should make almost no difference.
-Joe-
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98 Explorer (Lemon Law Case in Progress)
'00 F-150, X-cab, 4x4, Lariat, Off-road, Trailer Tow, Holandia Sunroof($1000), built 11/99 picked up 10/00!Clear Corners($36), Manik Stainless Steel 1-piece brush guard($700), Custom CB wiring, Uniden PC76-XLW CB radio($100) with K-40 Magna-Mount antenna (for now [$40]), 1 set of 165 watt KC Daylighters (for now... more on the way... $140) Fog Light Switch mod(free!!!), Custom switch mounting plate and overhead console, Bully Stainless Steel Trailer hitch drawbar w/ 2" stainless steel ball($80), Gray Tek Style Soft Tonneau Cover($250), Gray Line-X Bedliner ($450).
List of planned mods: Clear tails, torsion bar tweak, bug deflector, Chrome ORP rims.
93 Probe GT teal, OE rims painted to match, bone stock drivetrain, leaky exhaust.
The theory behind running the AC is just as you said: To dry the humidity out of the air. On most vehicles, the AC compressor will not cycle when it's below 45-50 degrees because, as you said, the air is already pretty dry at that point. I know in my Probe it cycles until it's around 35 degrees out, but it just varies from car to car. Does it put additional wear and tear on it? Yes, but it's marginal. Does it hurt the mileage? Minimally, but yes, in theory, it does. In our trucks, however, it should make almost no difference.
-Joe-
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98 Explorer (Lemon Law Case in Progress)
'00 F-150, X-cab, 4x4, Lariat, Off-road, Trailer Tow, Holandia Sunroof($1000), built 11/99 picked up 10/00!Clear Corners($36), Manik Stainless Steel 1-piece brush guard($700), Custom CB wiring, Uniden PC76-XLW CB radio($100) with K-40 Magna-Mount antenna (for now [$40]), 1 set of 165 watt KC Daylighters (for now... more on the way... $140) Fog Light Switch mod(free!!!), Custom switch mounting plate and overhead console, Bully Stainless Steel Trailer hitch drawbar w/ 2" stainless steel ball($80), Gray Tek Style Soft Tonneau Cover($250), Gray Line-X Bedliner ($450).
List of planned mods: Clear tails, torsion bar tweak, bug deflector, Chrome ORP rims.
93 Probe GT teal, OE rims painted to match, bone stock drivetrain, leaky exhaust.
Senior Member
Joined: Sep 2000
Posts: 231
Likes: 0
From: WustaMass, Where we pahk ah cahs!
Another reason is to keep the seals on the compressor lubricated to prevent them from drying out and cracking. 
ennis
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'98 White Super Cab 4X4 Lariat
WustaMass, Where we pahk ah cahs!
ennis------------------
'98 White Super Cab 4X4 Lariat
WustaMass, Where we pahk ah cahs!
Senior Member
Joined: Dec 1999
Posts: 749
Likes: 0
From: Lakeville, Minnesota, USA
After driving a vehicle that did not have a/c that ran with the defrost, I can tell you it makes a huge difference in the defroster effectiveness when the a/c kicks in. Thw vehicle without it fogged up like a SOB when it rained. The defrosters did nothing to help. Never a problem in the truck!
And it is a good thing to have the compressor run a little in the winter, like others have said. It keeps the seals in good shape. Both of my current vehicles, one a '89 chevy cavalier, still run the original refrigerant with no recharges, and the a/c works fine on both of them.
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1997 F150 XLT, Flareside , Moonlight Blue, 4x2, SC, Auto, 4.6L, 3:08's, Cargo Cover by Century, bed liner, Blue Oval reciever hitch plug, Driver Design bug deflector, Monroe Reflex Shocks, 235/70/16 Bridgestone Dueler AT's, sliding rear window, captain's chairs, Valvoline Durablend Oil, Purolator Pure One Oil Filter, and 125,000 miles and counting!
And it is a good thing to have the compressor run a little in the winter, like others have said. It keeps the seals in good shape. Both of my current vehicles, one a '89 chevy cavalier, still run the original refrigerant with no recharges, and the a/c works fine on both of them.
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1997 F150 XLT, Flareside , Moonlight Blue, 4x2, SC, Auto, 4.6L, 3:08's, Cargo Cover by Century, bed liner, Blue Oval reciever hitch plug, Driver Design bug deflector, Monroe Reflex Shocks, 235/70/16 Bridgestone Dueler AT's, sliding rear window, captain's chairs, Valvoline Durablend Oil, Purolator Pure One Oil Filter, and 125,000 miles and counting!
