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Heat pump iced up, blowing cool or on backup heat.

A trained tech should do energized checks, and a refrigerant-credentialed technician should do reversing valve and charge work.

Customers put it like this

  • The outdoor unit is a block of ice
  • It blows cool air on heat
  • Backup heat stays on all the time
  • The indoor unit we aren't using hisses
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Stop first if

  • Ice or water is on outdoor wiring or controlsKeep clear of it. A qualified person kills power at the disconnect while standing somewhere dry. Otherwise call a licensed electrician.
  • Panels must come off an inverter outdoor unitTreat it as live even when idle. A licensed tech locks out power, waits the label time, and measures the DC bus first.
01

Ask on the call

6

Homeowner? These are the questions a good technician will ask you. Having the answers ready makes the first visit count.

  1. Was it in heat or cool mode at the time?
  2. What was the weather like: humid, foggy or icy?
  3. Does the ice ever clear on its own?
  4. Do you hear a whoosh when it switches?
  5. Does it show a code?
  6. Is there one indoor unit or several?
02

Bring

5
  • Remote probe thermometers
  • Electrical meter
  • Clamp-on current meter
  • Clean filter
  • Flashlight
03

Check on site

6
  1. Record the mode and pull the wiring diagram.
  2. Judge any trip by the mode it happened in. Look at the coil that matters for that mode.
  3. On a multi-zone unit, compare what you see with the maker's documented routines first.
  4. A tech checks the valve coil and compares line temperatures across the reversing valve.
  5. A tech forces defrost by the maker's steps and watches the valve shift, outdoor fan stop and aux heat.
  6. If aux heat cycles, check airflow against the maker's minimum, then the limit. Remove every test jumper.
04

Keep on the record

5
  • Which mode it was in
  • Photo of the ice pattern
  • Line temperature readings at the valve
  • Defrost test result
  • Heater stage current

General guidance for a qualified person, not a finding about any home. The person on site decides.