What it is

A heat pump is an air conditioner that can run backwards to heat, so it does double the work and carries components a straight-cool system doesn't have: a reversing valve, a defrost control, and usually electric auxiliary heat. PM on a heat pump covers everything a cooling tune-up does plus those heat-mode-specific items. Because it runs year-round, a heat pump genuinely benefits from a look before both the cooling season and the heating season.

How it works

Everything that wears on an air conditioner wears on a heat pump too — caps, contactors, coils, drains — except a heat pump piles on more run hours and more stress. On top of that, heat mode introduces failure modes that simply don't exist on a cooling-only system: a reversing valve that sticks or leaks internally, a defrost board or sensor that won't clear frost from the outdoor coil, and auxiliary heat strips that may not be coming on (or may be stuck on, which quietly doubles the electric bill). A normal cooling PM never touches any of that, which is why a heat pump needs its own checklist.

In the field

Do the full cooling-PM sequence (filter, capacitor metering, condenser/coil cleaning, contactor, amp draws, condensate, electrical, charge verification) and add these heat-pump-specific steps:

  1. Clean both coils and respect the outdoor coil's heating role. In heat mode the outdoor coil is the evaporator, and it has to absorb heat from cold outdoor air. A dirty outdoor coil kills heating capacity and messes with defrost. Clean it like it matters in winter, because it does.
  1. Verify the reversing valve actually shifts. Command heat and cool and confirm the valve swaps and the system changes modes. A reversing valve that hangs between positions, or leaks internally, robs capacity in both modes — a classic "it kind of cools and kind of heats but never well."
  1. Test the defrost cycle. Confirm the defrost control initiates and terminates properly — the unit should switch to defrost, melt frost off the outdoor coil, and return to heating. A bad defrost sensor or board leaves the outdoor coil iced into a block, and the customer loses heat.
  1. Confirm auxiliary/emergency heat operation and staging. Verify the strips energize when they should (on a call for aux/second stage and during defrost) and — just as important — shut off when they shouldn't be running. Stuck-on strips are an invisible money leak; never-on strips leave the home cold on the coldest days.
  1. Check the balance-point/staging logic where applicable. Confirm the controls bring on supplemental heat appropriately for the home and equipment, and that any outdoor sensor or lockout is sane.
  1. Verify charge by the manufacturer's method and conditions. Heat-pump charging is fussier than straight cool — verify the way the maker specifies, and remember cold-weather charging has its own rules.
  1. Check the outdoor unit's drainage and mounting. In heating, the outdoor unit makes condensate (and defrost meltwater). Confirm it drains away and doesn't pool and refreeze around the base, which can damage the coil and fan.
  1. Document mode-by-mode — cooling readings, heating readings, defrost behavior, and aux-heat amps.

Normal values & targets

Residential heat-pump ballparks — defer to the equipment:

  • Auxiliary electric heat: strips draw heavy current (often tens of amps per strip); verify draw matches the nameplate kW when energized, and zero when they should be off.
  • Reversing-valve solenoid coil: ohms out to a typical small-coil resistance; compare to spec and confirm it actually moves the valve.
  • Defrost: initiates and terminates on the board's logic (time/temperature or demand); outdoor coil should be clear of frost after a cycle.
  • Cooling-mode split: ~16–22°F like any AC; heating performance is judged by the maker's method and the conditions, not a simple split.
  • Capacitor / amps / line voltage: same targets as a cooling PM (cap within ±6%, amps ≤ nameplate, ~240V nominal).

Common faults & what they mean

  • Weak heating, weak cooling, both lukewarm: reversing valve leaking internally or not fully shifting.
  • Outdoor coil iced into a block in winter: defrost not working — sensor, board, or reversing-valve issue during defrost.
  • Sky-high electric bills, house warm enough: auxiliary strips stuck on or staging logic bringing them in constantly.
  • House cold on the coldest days, strips never engage: aux heat not energizing — wiring, relay/sequencer, or control problem.
  • Water pooled and refrozen under the outdoor unit: drainage/mounting problem from defrost meltwater.

Tech tips & gotchas

Always make the reversing valve move during a PM. Commanding both modes and confirming the swap takes a minute and catches the sneaky "underperforms in both seasons" complaint that techs chase forever. An internally leaking valve looks like a charge problem until you realize it's hot and cold on the wrong sides.

Watch the auxiliary heat in both directions: it has to come on when needed and go off when not. A stuck contactor or sequencer feeding the strips can run up a brutal electric bill while everything "seems fine." Reading aux amps when they should be zero is a great catch.

Don't skip the outdoor coil cleaning thinking it's "just the condenser." In winter that coil is the evaporator absorbing heat from cold air — a dirty one tanks heating capacity and confuses defrost.

Time your visits to the seasons. A heat pump earns a spring look (for cooling) and a fall look (for heating and defrost) because it has two complete operating modes that each fail in their own way. Selling a single annual visit on a year-round machine leaves half its failure modes unchecked.

Cold-weather charge verification is its own skill — don't trust a quick gauge read on a frigid day; follow the manufacturer's cold-ambient procedure or wait for suitable conditions.

Safety / code notes

  • Auxiliary/emergency electric heat strips pull heavy current — confirm conductors, breakers, and sequencers are sized and rated per the nameplate; HVAC and electric-heat circuits fall under NEC Article 440 and Article 424 for fixed electric heating.
  • Lock out and discharge capacitors before electrical service; prove dead with a verified meter.
  • Outdoor-unit condensate/defrost water disposal shouldn't create an ice hazard or undermine the pad; mechanical-code drainage principles apply (IMC; Indiana enforces the IMC).
  • Verify the disconnect is in sight of the outdoor unit and the unit is grounded.