Ucm Control System - Trane S*HF*20-75 Troubleshooting Manual

Commonly Used Acronyms
Reset Amount Maximum.
An adjustable parameter on the HI where the maximum amount of reset allowed is defined.
Reset End Temperature.
The temperature at which the maximum reset amount will occur.
Reset Start Temperature.
The temperature at which reset will begin.
Return Fan Control. .
Return Fan Control is a feature which allows units to operate at a higher external or duct system
static pressure, or to reduce the load (horsepower requirement) on the supply fan motor. The fan is placed in the return
air path.
Return Fan Plenum Pressure.
The area between the Exhaust and Return Dampers and the outlet of the Return Fan
defines the return plenum. The absolute static pressure measured in this area is the Return Fan Plenum Pressure.
Return Plenum Pressure High Limit.
This control feature, available on all return fan options, shuts the supply fan and
return fan off if the pressure in the return plenum exceeds a non-adjustable setpoint of 3.5 iwc.
Space Pressure.
The pressure in the building as measured by the space pressure transducer, referenced to outside
(atmospheric) pressure.
Single Zone Variable Air Volume.
The active discharge air setpoint, used for cooling, heating and supply fan speed
control, is based on the zone temperature load conditions.
Supply Air Pressure High Limit.
A pressure limit to prevent unit casing and/or ductwork over pressurization.
Statitrac™.
A control method to maintain proper space pressurization.
Supply Air Pressure.
The pressure in inches-water-column (IWC) of the supply duct plenum or outlet as measured by
the supply air pressure transducer, referenced to local outside (atmospheric) pressure.
Supply Air Tempering.
An active heating mode where the supply air temperature has dropped below a preset value,
usually due to cold outside air being brought in to provide building ventilation.
Supply Air Temperature Control Point.
The revised value of SA Temp Setpoint after supply air temperature reset has
been applied.
Supply Air Temperature Reset.
A function that shifts the SA Temp Setpoint an amount based on the value of another
parameter—typically Zone Temp or Outdoor Air Temp. The purpose of this function is to lower unit capacity to better meet
load requirements.
Target Setpoints.
An internally calculated control point which is typically derived from other setpoints in combination
with specific unit operating conditions.

UCM Control System

Trane Large Commercial Rooftop Units are controlled by a microelectronic control system that consists of a network of
modules and are referred to as Unit Control Modules (UCM).
The unit size, type VVDA (VAV w/ IGV/VFD), SZxx (SZVAV), RRXX (Rapid Restart), CVDA (VAV w/o IGV/VFD), CVZT (CV),
VVZT (SZVAV), heating functions, peripheral devices, options, exhaust capabilities, etc. determine the number and type
of modules that a particular rooftop unit may employ.
The UCM receives analog or binary inputs, then processes this information and supplies outputs in the form of
modulating voltages, contact closures, etc. to control damper actuators, fan motors, compressors, valves, electric heating
coils and other electrical devices in the unit to maintain set comfort levels.
The UCM provides some equipment protection functions both directly and indirectly, such as duct pressure limits and
compressor lockouts.
Listed below are the various modules that may be employed in a UCM control system.
Rooftop Module (1U1 IntelliPak II / 1U48 IntelliPak I)
(standard on all units) The RTM is the central processor of the system. It continuously receives information from the other
unit modules, sensors, the remote control panel, and customer supplied relays. It then interprets this information and
8 RT-SVP07B-EN