Trane SCXG-SVX01B-EN Maintenance diagnostics, Low Air Temp Limit Trip, MCM Communications Failure

Maintenance diagnostics

designated the heat module auxillary temperature input as their input are disabled.

Reset Required: (PAR) An automatic reset occurs after the heat module auxillary temperature input returns to its allowable range for 10 seconds.

Heat Module Comm Failure Problem: The RTM has lost communication with the heat module.

Check: Check field/unit wiring between RTM and heat module.

Reason for Diagnostic: The RTM has lost communication with the heat module.

UCM Reaction: An “all heat off” request is sent to the heat operation function.

If the unit has staged gas or electric heat, all heat module outputs will be zeroed and deenergized.

If the unit has hydronic heat or chilled water installed, the unit will turn off the supply fan and close the outside air damper upon the occurrance of a heat module comm failure. A failsafe function in the heat module will cause all water valves to be set to 100% to provide full water flow. Unless used for switching purposes (air handlers with chilled water and mod gas, or chilled water and hydronic heat) all binary outputs will be deenergized.

Reset Required: (PAR) An automatic reset occurs after communication has been restored.

L

Low Air Temp Limit Trip

Problem: The low air temp limit has tripped. (Units with steam or hot water heating, or air handlers with chilled water cooling)

Reason for Diagnostic: A low air temp limit trip is detected continuously for more than one second. This can occur if the hydronic heat low air temp limit input closes for > 1 second, or if the chilled water low air temp limit trip input opens

for > 1 second. On units with both hydronic heat and chilled water, both low air temp limit inputs are active, and the unit will respond in the same manner regardless of which input is used.

UCM Reaction: The UCM will initiate the following actions;

a. An “open all water valves”request is issued to the heat module function, causing any steam, hot water, or chilled water valves on the unit to open.

b. An “all heat off” request is issued to the heat control function.

c. A “fan off” request is sent to the supply fan control function.

d. A “close damper” request is sent to the economizer actuator control function.

Reset Required: (PMR) A manual reset is required after the low air temp limit trip condition clears. The diagnostic can be reset at the unit mounted human interface, byTracer Summit, or by cycling power to the RTM.

Low Pressure Control Open - Circuit 1, 2, 3, or 4

Problem: The Low Pressure Control (LPC) for Ckt #1, 2, 3, or 4 is open.

Check: State of refrigerant charge for ckt #1, 2, 3, or 4.

Reason for Diagnostic: The Ckt # 1 LPC input is detected open as described in the compressor protection function.

UCM Reaction: A “Lockout Ckt # 1, 2, 3, or 4” request is issued to the compressor staging control function.

Reset Required: (PMR) A manual reset is required anytime after the diagnostic is set. The diagnostic can be reset by the human interface,Tracer Summit, or by cycling power to the RTM.

M

Manual Reset SA Static Press Limit Problem: The supply air static pressure went too high for the third consecutive time.

Reason for Diagnostic: The auto reset

supply air static pressure limit diagnostic has occurred for the third time while the unit is operating in occupied mode.

UCM Reaction: A "supply air pressure shutdown" signal is sent to the following functions;

a. Compressor staging control, b. Economizer actuator control, c. Heat operation,

d. Supply fan control, e. IGV/VFD control, f. Exhaust fan control

g. Exhaust actuator control

Reset Required: (PMR) A manual reset is required and can be accomplished at the HI,Tracer Summit, or by cycling power to the RTM.

MCM Communications Failure

Problem: The RTM has lost communication with the MCM.

Check: Check field/unit wiring between RTM and MCM.

Reason for Diagnostic: The RTM has lost communications with the MCM.

UCM Reaction: A “Lockout” request is sent to the compressor staging control function. And a failsafe function in the MCM will cause all MCM outputs to be zeroed and deenergized.

Reset Required: (PAR) An automatic reset occurs after communication has been restored.

Mode Input Failure

Problem: The RTM mode input is out of range.

Check: Sensor resistance should be between 1 ohm and 40 ohms. If so, check field/unit wiring between sensor and RTM.

Reason for Diagnostic: The mode input signal on the RTM is out of range (resistance < 1 ohm or resistance > 40 ohms).

UCM Reaction: The system mode reverts to the default (HI set) system mode.

Reset Required: (INFO) An automatic reset

108 SCXG-SVX01B-EN