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6. Protection functions:
● Outdoor coil temperature protection (T3)
i. If T3 > 143.6F, compressor is de-energized
ii. If T3 < 129.2F, compressor is energized
● Ambient temperature protection (T4)
i. If 50F ≤ T4 < 140F, unit can operate in cooling
ii. If -4F ≤ T4 < 86F, unit can operate in heating
iii. If T4 < 6.8F, heat pump will provide 24V control to indoor unit energizing electric heat (if installed.
● Discharge Temperature (DT) protection (T5)
i. If DT > 239F during cooling mode, the compressor will stop.
ii. If DT < 194F during cooling mode, the compressor will restart.
iii. If DT > 221F during heating mode, the compressor will stop.
iv. If DT < 167F during heating mode, the compressor will restart.
● High pressure protection (HPS) (mechanical open/close pressure switch)
i. HPS opens at P > 580psig, the compressor and outdoor fan stop.
ii. HPS closes at P < 435psig, the compressor and outdoor fan restart.
● Low pressure protection (LP)
i. If Low Pressure < 43.5 for 5 minutes during cooling mode, the compressor and outdoor fan will stop.
System will attempt to run again after 6 minutes.
● Module (inverter) protection (TF)
i. If TF > 176F, the compressor and outdoor fan will stop.
ii. If TF< 145F, the compressor and outdoor fan will restart.
4. Compressor Crankcase Heater Description
Refrigerant migration during the OFF cycle can result in noisy start-ups, therefore a crankcase heater (CCH) is
used to minimize refrigerant migration thereby minimizing start-up noise and/or bearing “wash out”. All CCHs
must be installed on the lower half of the compressor shell. Its purpose is to warm the compressor on the OFF
cycle, driving refrigerant from compressor. At initial start-up or after extended shutdown periods, allow CCH to
be energized for at least 12 hours prior to compressor operation by applying line voltage to heat pump with
thermostat OFF.
● CCH operation energizes:
1. First time line voltage is applied and compressor discharge temperature T5 < 104F.
2. In process of defrosting.
3. Compressor stops running for 4 hours and outdoor ambient temperature T4 < 50F or T5 < 104F.
● CCH operation de-energizes:
1. Compressor discharge temperature T5 ≥ 113F.
5. Reversing valve operation:
● Reversing valve energizes during heat mode and de-energizes in cool mode.
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