ERM5220R EQUIPMENT REMOTE MODULE
27 33-00205—01
FREQUENTLY ASKED QUESTIONS
#1 Q: Do I need an EIM (equipment Interface module) when using an ERM (Equipment remote module)?
A: It depends-
• If you are using a Prestige IAQ with ERM, the EIM is always required. For a heat-only application, use the EIM
only (no ERM).
• If using one of the 8000 RedLINK models (TH8110R, TH8320R, TH8321R) with a boiler for heat only, you can
use an ERM and do not need an EIM. (Thermostat needs 24 volts at Rc and C when EIM is not used).
• If using one of the 8000 RedLINK models (TH8110R, TH8320R, TH8321R) for outdoor unit AND you have
wires from air-handler to thermostat subbase you do not need an EIM. (Thermostat needs 24 volts at Rc and C
when EIM is not used)
• If you need to be wireless to outdoor unit AND indoor unit you need an EIM.
#2 Q: How many ERMs can I link to a single thermostat?
A: up to 2 ERMs can be linked per compatible thermostat. One for boiler and one for outdoor unit.
#3 Q: Can I link more than one thermostat to the same ERM?
A: No.
#4 Q: How do I verify compatibility?
A: See page 3.
#5 Q: What happens if communication is lost between ERM and thermostat?
A: If there is still power at the thermostat and it has not been removed from the wall, the thermostat will indicate
that signal was lost.
• If controlling a boiler with ERM and there is an indoor sensor wired to ERM, 30 minutes after communication
is lost “Freeze control
” is enabled, the ERM controls to 55 from the sensor reading.
• If controlling a boiler with ERM and there is not a sensor linked to ERM the boiler will not run, regardless of
temperature until communication is restored.
• If controlling an outdoor unit the outdoor unit will not run until communication is restored.
#6 Q: Do I need to wire a sensor to the S1 terminals on ERM?
A: No. If you do not use the indoor sensor when controlling a boiler, you would not have the “Freeze control”
(described in answer 5). If you do not use a wired sensor for the outdoor unit, the thermostat will not display
outdoor temperature unless the wireless outdoor sensor is used instead. Sensor are listed in Table 3 on page 3.
#7 Q: Are the terminals on the thermostat subbase or EIM (equipment Interface module) also energized when using the
ERM?
A: Yes.
• If linked to EIM and ERM, (and ERM set for boiler) they both get energized with a call for heat. So we close from
Rh to W at EIM and we close from T to T at ERM.
• When ERM is used for outdoor unit (ERM closes from R to Y and EIM closes from Rc to Y and G).
• With the TH8110R, TH8320R, or TH8321R series stat, if there is no EIM used, subbase of the stat closes the
switches in addition to ERM.
•EIM is always
required with PIAQ (THX9421R) even when used with ERM to boiler for heat only. So an ERM
would not make sense for those applications. Use EIM instead.
#8 Q: Can I use the ERM with a forced air zone panel?
A: No. The ERM is designed to link to a single thermostat (or thermostat + EIM). It cannot link to a zone panel. Do not
attempt a work-around (such as linking a separate ERM to each thermostat and wiring them in parallel). If this
were done we would have one or more of the following issues:
• We eliminate the purge delay on the panel. This is a minimum off time at the end of each cool cycle before it
attempts to run cooling again. If each thermostat is by-passing the zone panel and directly controlling
outdoor unit we could cycle off from one zone, and then 5 seconds later a different zone could call for cooling.
• The zone panel has logic to prevent heat and cooling from running at the same time. If each thermostat is by-
passing the zone panel and directly controlling outdoor unit we could be running the heat and AC at the same
time.
• For heat-pump operation, when configured for cool changeover, the ERM keeps the O/B changeover
energized continually after the cooling call until it sees a heat call. When configured for heat changeover, the
ERM keeps the O/B changeover energized continually after the heat call until it sees a cooling call. So there
could be a thermostat trying to call for heat, but the cool changeover is being energized by a different ERM or
vise-versa.
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