CH: Chiller
CHW: Chilled Water (T, P, DP, SP)
CW: Condenser Water (T, P, DP, SP)
VFD: Variable Frequency Drive 
VSD: Variable Speed Drive (York VFD)
AFD: Adaptive Frequency Drive (Trane VFD)
Comp or CP or C: Compressor
CKT: Circuit 
AO or AI: Analog Output or Input
BO or BI: Binary Output or Input
DO or DI: Digital Output or Input 
PLC: Programmable Logic Controller
SCR: Silicon Controlled Rectifier 
IGBT: Insulated Gate Bipolar Transistor 
DC Bus: Direct Current rail assembly in a VFD
S/S: Start/Stop signal to enable equipment 
CT: Cooling Tower or Current Transformer depending on context 
TR: Transformer 
IGV: Inlet Guide Vane
PRV: Pre Rotation Vane (York IGV)
VGD: Variable Geometry Diffuser 
O: Oil (T, P, DP, SP)
I/O: Input/Output
SAT: Saturated Temperature or Supply Air Temp depending on context 
LWT: Leaving Water Temp
EWT: Entering Water Temp
SH: Superheat
DSH or SSH: Discharge or Suction Superheat
EXV or EEV: Electronic Expansion Valve 
PRV: Pressure Regulating Valve or Pressure Relief Valve depending on context
GPM: Gallons Per Minute 
FTHD: Feet of Head, another way of representing water pressure 
D: Discharge (T, P, SH, DP)
LL: Liquid Line (T or P)
S or Suc: suction (T, P, SH)

The below can be applied to the above to represent a variety of different data. (e.g. CHWSP = Chilled Water Setpoint or CWT = Condenser Water Temperature) 
T: Temperature
P: Pressure or Pump depending on context (e.g. CHWP = Chilled water pressure or chilled water pump)
SP: Setpoint
DP or PD: Differential Pressure

This is not an exhaustive list but a lot of the common acronyms used.