HVACopediaBosch · Heat pump · Startup
Crankcase heater and reversing valve behaviour
What happens, in order
- Crankcase heater turns on when line voltage is first applied and discharge temperature (T5) is below 53.6F, or after the compressor has been off 3 hours with outdoor air below 41F or T5 below 53.6F
- Crankcase heater turns off when T5 reaches 60.8F or when the compressor starts
- After a long cold shutdown, leave line voltage on with the thermostat off for at least 12 hours before running the compressor
- Reversing valve is energized in heating and de-energized in cooling
- On the first heat call after power-up the unit runs about 1 minute in cooling so pressure builds enough for the valve to shift
- A pressure equalizer valve balances the system before compressor start
Timings and thresholds
| Item | Value |
|---|---|
| Heater on threshold | T5 below 53.6F |
| Heater off threshold | T5 60.8F or higher |
| Off-cycle trigger | Compressor off 3 h |
| Cold shutdown preheat | 12 h minimum |
| First heat call cooling run | About 1 min |
Applies to: Bosch IDS inverter heat pump condensing units
Models
More Bosch heat pump sequences
- Demand defrost · Defrost
- Manual (forced) defrost test · Defrost
- Oil return and force (charge) mode · Other
- Operating limits and compressor protections · Other
Related
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Source: Bosch IDS Light (BOVA15, R-454B) installation BTC 762003308 D, 17 System operation (17.3, 17.5, 17.6); Bosch IDS Premium Connected (BOVA36-60-20) installation BTC 762003301 D, 18 System operation (18.5, 18.6). Written in our own words; timings can differ by model and software version, so check the manual for your exact unit.
For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.