What it is

A packaged heat pump puts the entire system — compressor, both coils, the blower, the reversing valve, defrost, and usually electric backup heat — into one cabinet. Instead of an outdoor condenser tied to an indoor air handler by a line set, it's all in one box that sits outside, either on a ground pad with the ducts coming through the back (common on manufactured/mobile homes) or on a rooftop curb (light commercial). Conditioned air leaves the cabinet through supply and return duct openings; refrigerant lines never leave the box.

It's the same heat pump refrigeration loop you already know — reversing valve, both coils swap roles by season, defrost in winter — just self-contained. Because the refrigerant circuit is sealed and charged at the factory, you don't braze or evacuate on a normal install; you set it, duct it, power it, and start it.

How it's built

Inside the single cabinet you'll find, in their own sections:

  • Compressor — scroll on most modern units, single-phase (residential/mobile home) or three-phase (commercial).
  • Outdoor coil and outdoor (condenser) fan — the section exposed to outdoor air, on the "weather" end of the cabinet.
  • Indoor coil and the blower — on the duct end; the blower pushes conditioned air into the supply duct.
  • Reversing valve, accumulator, bi-flow metering, and check valves — the same heat-pump-specific plumbing as a split heat pump, all inside the box.
  • Defrost board and coil sensor — to handle outdoor-coil frost in heat mode.
  • Electric heat kit — backup/auxiliary strips, very common on packaged heat pumps since they often serve manufactured homes with no other heat source.
  • Controls — contactor(s), transformer, sequencers/relays for the strips, and the low-voltage terminal block.
  • Single-point power and a duct/curb interface — one power feed lands in the unit; the ducts connect through the cabinet's supply/return openings (down-flow through a curb on rooftops, or horizontal/back-duct on ground units).

How it differs from its cousins

  • vs. a split heat pump: same refrigeration circuit, but no field line set, no field brazing/evacuation, and the blower is built in. Diagnosis is similar; access is different — everything's in one cabinet outdoors.
  • vs. a gas/electric package (gas pack): a gas pack burns gas for heat with a flue and combustion air; a packaged heat pump heats with the refrigeration cycle plus electric strips and has no combustion at all. No CO concerns, no venting, but it leans on electric backup in cold weather.
  • vs. a packaged AC: the packaged AC has no reversing valve or defrost and can't heat with the cycle.

How it's wired and ducted

Power: a single 240V feed (single-phase residential, or three-phase commercial) lands at the unit's disconnect/whip. Because the electric heat is inside the same box, the single-point MCA/MOCP on the plate covers the whole unit including the strips — that feeder and breaker are sized for compressor plus heat. Control: a heat-pump thermostat with R/C/Y/G/O(B)/Aux/E, exactly like a split heat pump. Ducts: supply and return tie to the cabinet openings; on a rooftop the curb seals the duct connection and supports the unit; on a ground/mobile-home unit the ducts run through the back or bottom.

In the field — sequence of operation

Functionally identical to a split heat pump, just self-contained:

  • Cooling: Y energizes the compressor and outdoor fan, O sets the reversing valve to cool (typical), the outdoor coil is the condenser and the indoor coil is the evaporator, the built-in blower moves house air across the indoor coil.
  • Heating: the reversing valve flips (de-energized, typical), the indoor coil becomes the condenser releasing heat into the supply duct, the outdoor coil absorbs heat from outdoor air. Strips assist on an aux call.
  • Defrost: the board reverses to cool, kills the outdoor fan, and energizes strips to temper the supply air while the outdoor coil de-ices, then returns to heat.

Normal values & targets

  • Charge: factory-sealed; verify against the plate with subcool/superheat for the mode and conditions, or weigh-in if you've opened the circuit. Don't assume a sealed unit is correctly charged after a long life — leaks happen.
  • Temperature rise on electric backup: the strip rise band on the plate, commonly ~20–50°F depending on KW and CFM.
  • Element current: ~21 A per 5 KW at 240V, staged.
  • Defrost interval: every ~30–90 min of frosting-condition run, terminating on coil temp.
  • Three-phase (commercial): all three legs present and balanced; check rotation on three-phase scrolls (wrong rotation = no pumping, loud).

Common faults & what they mean

  • No heat from the cycle, strips carrying everything. Reversing valve stuck/not shifting, low charge, or defrost stuck — same heat-pump faults as a split, plus check the strips aren't the only thing working.
  • No cooling. Compressor/contactor/cap failure, or reversing valve stuck in heat.
  • Outdoor coil freezes over in winter. Defrost not initiating — board, coil sensor, or low charge.
  • Water/air leaks at the duct connection or curb. A bad curb gasket or duct seal on a rooftop unit dumps conditioned air and lets weather in — a packaged-unit-specific issue. Condensate must drain off the unit, not pool in the base.
  • Whole unit dead. Single-point power problem — disconnect, breaker, or the one feeder. Since everything shares one feed, a tripped breaker kills the entire unit.
  • Strips won't energize. Sequencer/contactor, open limit, blown fusible link, or aux not being called.

Tech tips & gotchas

  • It's a heat pump in a box — diagnose it like a split heat pump. Reversing valve, charge, defrost, and electric backup are the same systems; you're just working in one cabinet outdoors.
  • Check the duct/curb seal on rooftop package units. Air and water leakage at the curb is a classic package-unit complaint that masquerades as low capacity. A split system never has this failure point.
  • Single feeder means single point of total failure. A dead unit with no lights at all is usually power — check the disconnect and the one breaker before opening the refrigerant side.
  • Confirm the reversing valve energized state for this unit before diagnosing heat/cool. Same gotcha as any heat pump.
  • Verify charge even on a "sealed" old unit. Years of vibration outdoors cause leaks; a packaged heat pump short on charge mimics a bad valve.

Safety / code notes

  • Single-point power: the unit's data-plate MCA/MOCP governs the feeder and overcurrent protection; a disconnecting means within sight is required per NEC §440. Lock out and discharge caps before service.
  • Recover refrigerant per EPA Section 608; never vent, even on a factory-sealed unit you have to open.
  • Rooftop work is fall-hazard work — follow fall protection and watch curbs/edges. The curb must properly support the unit and seal the duct opening; condensate drains per code, not onto the roof membrane.
  • Electric heat conductors/overcurrent per NEC and the plate; blower-strip interlock is a safety.