Trane R Series, Installation Operation & Maintenance

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RLC-SVX07A-EN 63
Installation - Electrical
- Low ambient run inhibit
- External AUTO/STOP input opened
The “RUN:UNLOAD” operating mode commands the compressors to
completely unload, which takes about 1/2 minute. This will allow the
compressors to be totally unloaded for the next startup. If only the proof of
chilled water flow interlock is used, the chiller will shut down on an immediate
(non-friendly) shutdown and initiate an automatic reset diagnostic.
Figure 27 shows a typical interlock of an RTWA or RTUA chiller. There are
three terminals (six wires) on the chiller that are required to be connected.
1. External Auto/Stop (Terminals 1U1TB3-3 and -4).
This input is supplied by the field. A contact closure will start the chiller
water pump and chiller, via the UCM pump control contacts. Opening the
contact will put the operating compressors into the “RUN: UNLOAD”
mode and initiate a timing period (1 to 30 minutes, adjustable through the
Clear Language Display). This will delay termination of the chilled water
pump operation via the UCM pump control contacts. Examples of the
input at terminals 1U1TB3-3 and -4 would be a time clock, ambient ther-
mostat, building automation system, etc.
2. UCM Pump Control Contacts (Terminals 1U1TB4-8 and -9).
This output is a set of contacts that will close and start the chilled water
pump when the external Auto/Stop contacts are closed. When the con-
tacts are opened, 1 to 30 minutes later (adjustable through the Clear Lan-
guage Display), the UCM pump contacts open.
3. Proof of Chilled Water Flow Interlock (Terminals 1U1TB3-1 and -2).
This terminal must be field installed. Contact closure between the termi-
nals indicate proof of chilled water flow. Examples of this is a pump
starter auxiliary contact, flow switch, differential pressure switch, or a
contact from a building automation system (see
"Chilled Water Flow
Switch on Page" 33 ). Opening of this contact will immediately shutdown
the chiller and initiate an automatic reset diagnostic, indicating loss of
chilled water flow.
Condenser Water Pump
For the condenser water pump interlock on the RTWA units, connect leads
565 and 566 between terminals 1TB4-1 AND 1TB4-2 in the upper portion of
the control panel and the condenser water pump control. The circuit is 115
VAC and the load is not to exceed 1150 VA inrush, 115 VA sealed.
This will interlock the condenser water pump operation with the unit
operation. This insures that the condenser water pump is operating before
the compressor(s) are started.