Why do cabs reduce PTO horsepower in some tractors?

[Magicman710]

I was comparing the PTO HP of several John Deere tractors, and I noticed that between a OOS and a cab, some of them loose as much as 3-6 HP in the cab models.

For example the OOS 5055E has 45 advertised PTO HP, but with a cab it goes down to 41.

The 5075E 61 HP with the OOS, but down to 57.2 with a cab.

However, the 5085 and 5100E does not loose any HP with a cab compared to OOS.

 

[bcp]

Power to run the AC compressor?

Bruce

 

[AaronS]

Power to run the AC compressor?

Bruce

That's my guess as well. Worth it to me with the allergies I have.

 

[Gary Fowler]

Some cabs don't have AC so no power drain. I rather doubt that you would consistently loose 5 HP due to compressor use mainly because they don't run all the time but you would see some lose. Most of the time, you wont even notice the power loss on a CUT because the power to weight ratio is fairly high. Not too many folks run equipment that fully loads the engine of their CUT tractors, so I wouldn't worry much about the lose.

 

[Magicman710]

Some cabs don't have AC so no power drain. I rather doubt that you would consistently loose 5 HP due to compressor use mainly because they don't run all the time but you would see some lose. Most of the time, you wont even notice the power loss on a CUT because the power to weight ratio is fairly high. Not too many folks run equipment that fully loads the engine of their CUT tractors, so I wouldn't worry much about the lose.

The 5085 and 5100 do have AC, but lose no HP from it.

My guess was the AC compressor as well, but as you say 4-5 HP seems like an awful lot.

 

[bcp]

AC uses more than most people think.

From:
Automotive Air Conditioning Bulletin Board

"Early compressors like a York, an RV2, or an A6, drag from 14-22 hp causing a great deal of fuel consumption and engine overheating.

Modern axial and scroll compressors take anywhere from 4 to 8 HP. Radial compressors are less efficent, demmanding from 7 - 12 HP."

==============================
And a dyno test here:

Easy way to loss 15whp - dyno'd with A/C on and off - NASIOC

Post 4

"The peak with A/C off is 222whp @ 5700 rpm
The peak with A/C on is 208whp @ 6400 rpm"
===========

Bruce

 

[Tx Jim]

The 5085 and 5100 do have AC, but lose no HP from it.

The only reason a 5085 & 5100 lose no HP from AC is because the AC switch was turned OFF!!!!!! AC compressor requires HP when it's turning.

 

[Labrat]

You also have to consider how much electrical load the clutch, condenser and evaporator fans are putting on the alternator. It also depends on what conditions they are running, Higher load means higher pressures or higher mass flow and more power is required to turn the compressor. Not sure what compressor JD is using but most automotive compressors are now variable displacement swash or wobble plate. The plate will actually stand up or lean down shortening/lengthening the piston stroke depending on load conditions this makes a significant difference on compressor power consumption.

 

[Gary Fowler]

If an automotive compressor requires that much HP (12) to cool such a small space, how do whole house units do it with such small motors. My 5 ton house unit is rated at 23 LRA amps @ 220 volts. Per formula on internet, that comes to 4.4 HP. That size unit would have snow flakes coming from the vents on a car, so why do auto/tractor compressors require so much power?

 

[Gary Fowler]

AC uses more than most people think.

From:
Automotive Air Conditioning Bulletin Board

"Early compressors like a York, an RV2, or an A6, drag from 14-22 hp causing a great deal of fuel consumption and engine overheating.

Modern axial and scroll compressors take anywhere from 4 to 8 HP. Radial compressors are less efficent, demmanding from 7 - 12 HP."

==============================
And a dyno test here:

Easy way to loss 15whp - dyno'd with A/C on and off - NASIOC

Post 4

"The peak with A/C off is 222whp @ 5700 rpm
The peak with A/C on is 208whp @ 6400 rpm"
===========

Bruce

I suppose the with this info, a 20 HP CUT with a cab, which would be substantially the same size as 100 HP tractor and require the same size compressor unit, would just about stall out when using the AC but they don't so something is skewed with all those figures. On cars, you can hear the idle speed fall a bit when turning on the AC but on my tractor, I don't notice any change at all in the engine speed. Someone care to explain how that HP is pulled from the engine on smaller tractors and them still be able to move from their tracks, i.e. 20 HP reduced to 8 HP via AC compressor would likely not even pull itself on flat ground especially when you remove another 5 HP to supply the HST so you only have a 3 HP tractor!!!!!!!