Bosch SM Series Installation, Operation And Maintenance Manual page 21

SM Split AH/AV Air Handler
Some options will have a built-in delay, and
hence, compressor operation is not
immediate.
When the thermostat calls for second-stage
cooling (Y2) the second stage (or full-compressor
capacity) is initiated. The fan ramps up to full
cooling airflow.
Once the thermostat is satisfied, the compressor
shuts down and the fan ramps down. If the "G"
terminal is still energized (fan operation is on
"continuous" at the thermostat) the fan will ramp
down to fan only air flow in 30 seconds. If the "G"
terminal is de-energized with "Y1" then the fan
ramps down to off in 30 seconds.
A fault condition initiating a lockout will
de-energize the compressor irrespective of
which stage is engaged.
Heating Mode
The first two stages of heating (Y1 & Y2) operate in
the same manner as cooling, but with the reversing
valve de-energized. On a call for auxiliary heat
(W1), the fan ramps up to auxiliary heat airflow
immediately and the electric heater package is
energized along with the compressor. As the
thermostat is satisfied, the heaters will shut off as
soon as W1 is de-energized, and the compressors
will remain on until the thermostat stages are
satisfied.
If the unit compressor lock out for any
reason at this time, the electric heaters will
continue to function normally.
Once the thermostat is satisfied, the compressor
shuts down and the fan ramps down to either
fan-only mode or off over a span of 30 seconds. If
thermostat has two different output points, one
for Auxiliary heat and a different one for
Emergency heat, the two outputs must be
terminated on W1 units equipped with one stage
of Electric heat.
Emergency heat (W2/EM) energizes the
emergency heat relay in the heater control box,
bringing on all of the heating elements at once. The
fan immediately ramps up to full electric heat
airflow.
SM Split AH/AV Air Handler
When using a 2-cool, 3-heat thermostat
both the W1 & W2 on the Heat Pump and
W2 & EM on the thermostat must be
connected together via a jumper.
Subject to change without prior notice
Sequence of Operation | 21
8733826256 (2020/06)