505232 06/07
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NOTE − High−temperature PEPI disables W2, E and Y1 (in heat mode only)
when ambient temperature exceeds 95F.
Table 8. 81M28 Output Characteristics
(with electric heat backup and no outdoor sensor)
Mode Outputs Activated
First−stage heat pump − cool Y1, G, O
Second−stage heat pump − cool Y1, G, O, Y2
First−stage heat pump − heat Y1, G, B
Second−stage heat pump − heat (Combina-
tion of heat pump and electric backup heat)
Y1, G, B, W2
First−stage emergency heat E/W1, G, B
Second−stage emergency heat E/W1, G, B, W2
81M28 Output Characteristics (with electric or gas (dual
fuel) heat backup and outdoor sensor)
The above output characteristics become restricted when high and low bal-
ance points are used.
1. Balance points are used only when the outdoor temperature sensor
(46M98) is attached to the unit.
2. When the thermostat is in heat mode and a heat demand exists, if the
temperature measured by outdoor sensor is below the low balance
point, the heat pump is turned off and only the electric (or gas) heat
can cycle.
3. When the thermostat is in heat mode and a heat demand exists, if the
temperature measured by outdoor sensor is above the high balance
point, the electric (or gas) heat is turned off and only the heat pump
can cycle.
4. When the thermostat is in heat mode and a heat demand exists, if the
temperature measured by outdoor sensor is between the high and low
balance points, both the heat pump and electric (or gas) heat and can
cycle.
5. Emergency heat is enabled whenever it is selected by the user (and
a heat demand exists) and is NOT restricted by the balance points.
NOTE − See figure 7 for a detailed flowchart of Dual Fuel operation.
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