Ingersoll-Rand ReliaTel, Manual, Page: 157 / 176

RT-SVD03L-EN 157
Circuits
Snubber Circuits
N No otte e:: Obsolete - Not Available to Order.
ReliaTel™ controls utilize relays to energize alternating
current (AC) loads. Because of the characteristics of AC
loads dealing with inrush current, snubber circuits are
used.
The purpose of a snubber circuit is to act as a filter to
help dampen the voltage peaks associated with the
opening and closing of the relay contacts. The snubber
circuit is a resistive/capacitive circuit, with a resistor
and capacitor wired in series across the on-board relay
contacts.
Snubber circuits may cause confusion because 24 vac
will be present if the output wire is disconnected from
the load; such as a relay or contactor coil, and the
contacts of the board relay are open. The voltage
potential between the disconnected wire and ground
will be 24 vac, but no current will be present. When the
wire is placed back on the contactor coil, the 24 vac
potential will disappear. To properly verify whether
voltage is present to energize a relay and contactor, the
circuit must be complete and in tact.
Figure 100. Snubber circuits
Resistor
Capacitor
Relay Contacts
24VAC Power
Supply
(On Board)
24VAC Output
to Load Being
Controlled.
(Off Board)
High Pressure and Low Pressure
Lockout Circuits
High pressure cutout (HPC) and low pressure cutout
(LPC) circuits are designed to shut compressor
operation down when pressures are too low, such as
loss of charge; or too high, such as would result from
dirty condenser coils.
The operational logic of these circuits is somewhat
unique and requires explanation to fully understand
how they operate.
LPC Logic
LPC logic was changed with version 3.1 of the RTRM.
Timing was changed from two minutes to 10 seconds
to enhance compressor reliability due to no-flow issues
for the TXV option during compressor starts.
However, due to unexpected compressor lockout
issues, the timing was again revised with version 6.0 of
the RTRM. The timing function will be different
depending on the outdoor temperature. If the OA temp
is below 40ºF, the timing is one minute. If OA Temp is
40ºF or above, timing is 30 seconds.
For RTRM version 8.0 + the timing has been revised
and is still dependent on outdoor ambient temperature.
If the outdoor temperature is less than 40ºF the LPC
bypass delay will be set to 60 seconds. When the
outdoor temperature is between 40 to 49.9°F the delay
will be set to 30 seconds. For all outdoor temperatures
50°F and above, there will be no delay in setting a LPC.
These delays will apply to all units.
LPC Sequence of Operation
On a call for cooling, there is an LPC bypass delay
period (depending on OA Temp) where the LPC switch
is ignored. If there is a low charge condition or low
pressure condition due to extreme cold ambient
conditions, the unit is allowed to run for the delay
period to build up pressure.
If the switch is closed after the LPC bypass delay time,
the compressor will continue to run. If the switch is
open, the compressor will shut down immediately.
After three minutes, if there is still an active call for
cooling, the unit will once again start. If the switch is
still open after the initial LPC bypass delay time, the
compressor will again shutdown. The unit will try to
start four times. If the switch is still open after the
fourth try, the unit will shut down and be locked out,
and will require a manual reset to start the unit again.
If the switch is closed and the compressor continues to
run for three minutes, the counter is reset and the logic
sequence starts over.
If the call for cooling goes away at any time during the
routine, the counter is reset and the logic sequence
starts over.
N No otte e:: If the unit is configured as a heat pump and is
actively heating with the outdoor ambient
temperature at or below 0ºF, or the unit is in an
active defrost mode, the LPC inputs will be
ignored.
LPC Operation for 27.5 to 50 Ton Units
with Modulating Reheat
Units configured with modulating dehumidification will
control compressors in regards to the compressor 1
and 2 disable inputs slightly different than traditional
units and will also include an extra LPC switch
connected to the RTDM. The following describes the
implementation of this function for these units:
• RTRM compressor 1 disable input will function as
today's units function.
• If active on a dual circuit unit, only circuit 1 will de-
energize after the appropriate delays during active
cooling. Both circuits will de-energize during active
reheat (circuit 2 after its minimum on timer
expires).