HVACopediaBosch · Heat pump · Defrost
Demand defrost
What happens, in order
- Demand defrost control watches the outdoor coil (T3) against outdoor air (T4), run time and high pressure
- Any one condition starts defrost (1) coil-to-air temperature difference reaches the target for 3 minutes: air 39F or above needs 18F, 30F or above needs 16F, 19F or above needs 14F; below 19F air with coil under 9F needs 80 minutes of accumulated compressor run
- (2) minimum run time elapsed 4 hours when air is below 23F; 2 hours when air is 23F up to about 40F (42F on IDS 2.0)
- (3) high-pressure saturation temperature stays below 82F for 20 minutes (Light and Premium Connected limit this to air between 14F and 29F)
- Display shows dF with the compressor frequency while defrosting
- Defrost ends when the outdoor coil reaches 64F for 1 minute, or after 8 minutes
- SW5 options shorten heating time 10 percent, or extend defrost (120 s on Light, 60 s on Premium Connected and IDS 2.0)
Timings and thresholds
| Item | Value |
|---|---|
| Delta T, air 39F or above | 18F |
| Delta T, air 30F or above | 16F |
| Delta T, air 19F or above | 14F |
| Delta T hold time | 3 min |
| Run time, air below 19F and coil below 9F | 80 min |
| Minimum run time, air below 23F | 4 h |
| Defrost end | Coil 64F for 1 min, or 8 min max |
| Low-pressure defrost trigger | Below 82F saturation for 20 min |
Codes you may see during this
Applies to: Bosch IDS inverter heat pump condensing units
Models
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Source: Bosch IDS Light (BOVA15, R-454B) installation BTC 762003308 D, 17 System operation; Bosch IDS Premium Connected (BOVA36-60-20) installation BTC 762003301 D, 18 System operation; Bosch IDS 2.0 (BOVA-36-60HDN1) service manual Rev3 07.2021, 10.2 Other operations. 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.