Originally Posted by JRMDC
It isn't just a matter of what CSX calls them. The AH is a "H"eavier engine, so higher low-speed tractive effort, along with software oriented toward tractive effort, better for low-speed coal heading uphill. To my knowledge CSX has no ES44AC units but it has both CW44AC and CW44AH models.
the "H" in "AH" stands for "High" as in "High Tractive Effort". CSX has heavy DC traction units, the ES40DC's. Being DC traction units and lacking radial or steerable trucks they do not conform to the High Tractive Effort specification.
CSX does have ES44AC's, they just choose to class them as ES44AH. Likewise UP has ES44AC's though they choose to class them as C45ACCTE. Additional ballast, steerable trucks, HTE software, CTE (control tractive effort), distributed power hardware/software, cab signals, ect. are all options chosen by a specific railroad. They are all ES44AC's and the railroad just specifies what it wants added to its units.
A large portion of the 700 and 800 series were delivered from GE stenciled as ES44AC and lacking the lightning bolt under the cabside number. This was a mistake by GE and was corrected with subsequent new deliveries having the ES44AH classification and lightning bolt applied.
Also, the ES44C4 is intended as a replacement for the ES44DC. The ES44C4 with its 4 AC traction motors is capable of producing tractive effort levels equivalent to the ES44DC with its 6 DC traction motors. BNSF is the only road to have ordered the ES44C4 sofar.