4
DATS Temperature / Resistance Chart
Table 3. DATS Temperature / Resistance Chart
Sensor
°C °F (ohm)
VDC
(Volts)
Sensor
°C °F (ohm)
VDC
(Volts)
-6.6 20 46,134 1.513 46.2 115 4,169 0.304
-3.9 25 39,869 1.425 49.0 120 3,749 0.277
-1.1 30 34,520 1.335 51.8 125 3,368 0.252
1.7 35 29,936 1.247 54.5 130 3,037 0.229
4.4 40 26,104 1.161 57.3 135 2,750 0.209
7.2 45 22,764 1.077 60.0 140 2,489 0.191
10.1 50 19,842 0.993 62.8 145 2,250 0.174
12.8 55 17,406 0.916 65.7 150 2,033 0.158
15.6 60 15,294 0.842 68.5 155 1,847 0.145
18.4 65 13,442 0.772 71.3 160 1,678 0.132
21.2 70 11,849 0.706 73.9 165 1,536 0.121
23.9 75 10,501 0.647 76.8 170 1,397 0.111
26.7 80 9,282 0.589 79.7 175 1,272 0.101
29.5 85 8,233 0.537 82.2 180 1,170 0.094
32.3 90 7,322 0.489 85.1 185 1,070 0.086
35.0 95 6,523 0.445 87.8 190 982 0.079
37.8 100 5,819 0.405 90.8 195 895 0.072
40.6 105 5,193 0.368 93.4 200 829 0.067
43.4 110 4,654 0.335
Pressure Switch
(Required for heat pump applications.)
NOTE: Outdoor unit (heat pump) will not operate if
pressure switch is not installed)
HIGH PRESSURE
SWITCH (27W13)
NEW SERVICE
VALV E DEPRESSOR
TEE (LENNOX 87071)
Figure 5. Tee and Vapor Line High Pressure
Switch
A eld-provided HFC-410A high pressure switch (catalog
number 27W13) is required for applications with a Lennox
heat pump. This switch protects the system in the event a
high pressure condition occurs in the outdoor unit during
heating mode. The switch operates in tandem with the
factory installed high pressure switch, but connects to the
iHarmony control instead. The switch is an auto-reset type
that opens at 550 psig and closes at 425 psig.
NOTE: If a pressure switch is factory installed in the
outdoor unit, do not remove the switch or switch
wires.
The damper control module pressure switch may also
be fastened directly to the vapor valve service port using
a eld-provided tee adapter. This line becomes the
discharge line in heat pump heating mode. Recommend
using pressure switch valve tee adapter (catalog number
87071).
Other conditions:
• Pressure switch status is used only for the heat pump
heating and does not have any affect on non-zone
demands.
• Heat pump will stop after the pressure switch status
remains open for 60 seconds.
CAUTION
High Pressure Switch must be installed on open side of
tee rst to prevent refrigerant loss.
Pressure switch 27W13 should be installed near air
handler or indoor coil. If installed at outdoor unit, a separate
2-wire conductor must be used for communicating outdoor
systems.
Staged Heat Pump Units
Should the pressure switch open during heat pump
heating second stage operation:
• Lennox communicating thermostat will downstage the
heat pump from second-stage to rst-stage heating
operation in order to bring the system pressure down to
a point where the switch closes again.
• If the unit is already running in rst-stage when the
pressure switch opens, the unit will shut off.
• If the switch closes within 60 seconds, then the Lennox
communicating series thermostat may send a demand
for second-stage heat pump if needed.
• If the switch does not close within 60 seconds, the
Lennox communicating thermostat stops heat pump
heating and satises the heating demand with backup
heat (backup heat is either electric or gas) regardless of
the ambient temperature being above the high balance
point.
The heat pump is used again on the next call provided
the pressure switch has closed; otherwise backup heat
is used on subsequent heating calls until the pressure
switch closes.
Modulating Heat Pump Unit (XP20 and XP25)
If the pressure switch opens during heat pump heating
operation:
• Lennox communicating series thermostat will respond
by sending a HP heat demand with the demanded rate
equal to the current rate 25%. (i.e. the switch opens
during a 90% heating demand,
• Lennox communicating thermostat then sends a
demand for 90 25 = 65%) If new calculated rate is below
the minimum for the unit, minimum demand is sent.
• If the switch closes within 60 seconds, then the Lennox
communicating series thermostat may change the
demand for the heat pump as determined by the DATS.
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