Winter MPG Experiment
Hotshot
Joined: Jun 2006
Posts: 15,450
Likes: 3
From: Hampstead, NC
Did you know that any time you turn the vent select **** to the right that it activates the AC compressor? Not true. Only on the AC settings and defrost does it run. I could be wrong, but I think that one piece of hardware uses about 5 HP to operate. AC Parasitic drag is very minimal, and only cycles in winter use, so it's minimal I read a number one time - stating it takes about 60 HP to keep our trucks at highway speed (60-65 MPH) on the flat with no wind. If I add that 5HP load when I want warm feet, that's close to a 10% hit on my fuel economy. Again, just on feet setting you are not using the compressor
Post Fiend
Joined: Sep 2003
Posts: 6,096
Likes: 27
From: Mesa AZ
There are 8 positions ranging from 9 o'clock to 4 o'clock.
Under normal operations the A/C compressor function is:
- Max A/C: A/C Compressor enabled
- A/C: A/C Compressor enabled
- Vent: A/C Compressor is disabled
- Off: A/C Compressor is disabled
- Panel/Floor (bi level): A/C Compressor enabled
- Floor: A/C Compressor disabled
- Floor/Defrost: A/C Compressor enabled
- Defrost: A/C Compressor enabled
In cases when the A/C compressor is enabled, it can still cycle on and off when needed.
Thread Starter
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Hotshot
Joined: Jan 2011
Posts: 18,849
Likes: 179
From: Puget Sound
Well... I learned a drawback to this experiment. I was driving along and my boost gauge dipped a bit for the speed I was driving. I checked all my gauges, including the overhead temp gauge. Ah... now I see what's going on. I was at about 5000 feet elevation on the flat and it was 10 degrees F, so the EBPV was slightly engaged to keep the engine warm. If the AC compressor was on, it might have introduce some warm air into the nose, maybe added a little load, or maybe would have done nothing. I am now shopping for something to block the air through the nose on cold days. I did this the first year I had the truck with a piece of cardboard behind the grill... but that made a mess and I skipped this the next winter. Now that I know more about the truck, I feel I should do something about this.
Junior User
Joined: Jul 2008
Posts: 61
Likes: 0
From: North Idaho
I have a Fia winter cover. It comes with crappy stick on snaps. I used them the first year but most fell off, even with prepping the surface. I now have stainless screw on snaps (marine type). I think I ordered the snaps off eBay and the cover from amazon.
Butt-Head
Joined: Apr 2004
Posts: 9,457
Likes: 2,938
From: Reed Point, MT
There is a flaw in your plan.....
The air conditioning system has a low pressure cycling switch.
Refrigerant has a low boiling point meaning that the pressure changes with ambient temperatures in which humans can survive.
Most low pressure cycling switches won't allow compressor clutch engagement below 20-25 PSI (as it hints to a low refrigerant charge during sane temperatures).
See this chart.
The A/C compressor won't run when it's really cold.
The air conditioning system has a low pressure cycling switch.
Refrigerant has a low boiling point meaning that the pressure changes with ambient temperatures in which humans can survive.
Most low pressure cycling switches won't allow compressor clutch engagement below 20-25 PSI (as it hints to a low refrigerant charge during sane temperatures).
See this chart.
The A/C compressor won't run when it's really cold.
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Thread Starter
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Hotshot
Joined: Jan 2011
Posts: 18,849
Likes: 179
From: Puget Sound
That's something I never knew. Very interesting. I still see the AC compressor cycle on cold days (hooked it back up), so this makes me wonder if my system is overcharged, or the heat from the engine plays a role. I need to see under what conditions my compressor cycles, but I'm not dedicated enough to stand in front of Stinky in the cold to check on it. Maybe I'll install an LED like the GPR... or just let it go. I vote the latter.
Cargo Master
Joined: Mar 2006
Posts: 2,502
Likes: 2
From: Bend Oregon
There is a flaw in your plan.....
The air conditioning system has a low pressure cycling switch.
Refrigerant has a low boiling point meaning that the pressure changes with ambient temperatures in which humans can survive.
Most low pressure cycling switches won't allow compressor clutch engagement below 20-25 PSI (as it hints to a low refrigerant charge during sane temperatures).
See this chart.
The A/C compressor won't run when it's really cold.
The air conditioning system has a low pressure cycling switch.
Refrigerant has a low boiling point meaning that the pressure changes with ambient temperatures in which humans can survive.
Most low pressure cycling switches won't allow compressor clutch engagement below 20-25 PSI (as it hints to a low refrigerant charge during sane temperatures).
See this chart.
The A/C compressor won't run when it's really cold.
Since the evaporator is in cab won't it see in cab tempeture and allow the refrigant to evaporate keeping the system functioning regardless of outside air temp?
Observation: my ac was out winter before last and I had a hard time keeping my windows from fogging. This winter and last I can have my whole family along 3 kids and the wife and I am fog free even with sub zero outside temps.
Butt-Head
Joined: Apr 2004
Posts: 9,457
Likes: 2,938
From: Reed Point, MT
The volume of the evaporator is comparatively small in relation to the accumulator, condenser, lines, and compressor but I guess it's possible......
None of the equipment/trucks at work (including my own car or pickups) are doing anything about compressor engagement at -20 regardless.
Your results may vary.
None of the equipment/trucks at work (including my own car or pickups) are doing anything about compressor engagement at -20 regardless.
Your results may vary.
Mountain Pass
Joined: Oct 2005
Posts: 191
Likes: 0
From: NH
I have always had a switch to turn off my a/c compressor. I find that it defrosts the windshield faster in the winter if the temps are mild. If its real cold..... a/c doesnt run. Other than winter blend fuel.....my mph goes down as soon as i start letting my truck warm up in the morning. Usually 10 min. I'm in NH by the way.
Cargo Master
Joined: Aug 2009
Posts: 2,137
Likes: 13
From: Glendive, MT
Question and observation:
Since the evaporator is in cab won't it see in cab tempeture and allow the refrigant to evaporate keeping the system functioning regardless of outside air temp?
Observation: my ac was out winter before last and I had a hard time keeping my windows from fogging. This winter and last I can have my whole family along 3 kids and the wife and I am fog free even with sub zero outside temps.
Since the evaporator is in cab won't it see in cab tempeture and allow the refrigant to evaporate keeping the system functioning regardless of outside air temp?
Observation: my ac was out winter before last and I had a hard time keeping my windows from fogging. This winter and last I can have my whole family along 3 kids and the wife and I am fog free even with sub zero outside temps.
Cargo Master
Joined: Aug 2009
Posts: 2,137
Likes: 13
From: Glendive, MT
Winter MPG's drop due to a whole host of things. Winter blend fuels play some role but the major factors are longer warmup times, for all systems on the truck. Grease in wheel bearings gets stiff as tar. Tire rooling resistance increases due to stiffening rubber and side walls. Transmissions never reach their most efficient opperating temp. The same goes for differentials and powersteering systems.