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Thermostat Wiring Diagrams for South Florida Homes

Common wiring configurations found in Miami-Dade, Broward, and Palm Beach County homes, organized by system type and era.

Standard Wire Color Reference

Wire Terminal Function Present In
Red R (Rh/Rc) 24V power from transformer All systems
White W (W1) Stage 1 heat Heat pump, gas furnace
Yellow Y (Y1) Stage 1 cooling (compressor) All AC systems
Green G Indoor fan (blower) All systems
Blue C Common (24V return) Smart thermostats
Orange O Reversing valve — cool Heat pumps (Carrier, Trane)
Orange B Reversing valve — heat Heat pumps (Rheem, Ruud)
Brown/Pink W2/Y2 Stage 2 heat/cool Two-stage systems

Critical: Colors are conventions, not standards. A white wire might connect to Y if the installer ran out of yellow. Always verify at both ends — the thermostat terminal AND the air handler terminal board.

Configuration 1: Standard AC (Most Common)

Found in: ~70% of South Florida homes with central AC and electric heat strip

Thermostat          Air Handler
─────────          ───────────
R  ←── Red ──────→  R  (24V hot)
Y  ←── Yellow ───→  Y  (compressor contactor)
G  ←── Green ────→  G  (blower relay)
W  ←── White ────→  W  (heat strip relay)
C  ←── Blue ─────→  C  (24V common)

Smart thermostat compatible: Yes, if C-wire present. If no C-wire (4-wire system): R, Y, G, W only. See C-wire solutions in main README.

4-Wire to 5-Wire Upgrade

If your existing cable only has 4 conductors (R, Y, G, W):

Option A — Add-a-Wire Kit:

  • Install add-a-wire module at air handler
  • Module converts one existing wire to carry both its signal AND the C signal
  • No new cable needed

Option B — Run new cable:

  • Replace 18/4 cable with 18/5 (adds blue C-wire)
  • Route through same path as existing cable (usually attic)
  • Tape new cable to old cable and pull through

Configuration 2: Heat Pump (Newer Construction)

Found in: Newer South Florida homes (2010+) with heat pump systems

Thermostat          Air Handler
─────────          ───────────
R  ←── Red ──────→  R   (24V hot)
Y  ←── Yellow ───→  Y   (compressor)
G  ←── Green ────→  G   (blower)
O  ←── Orange ───→  O   (reversing valve)
W2 ←── White ────→  W2  (aux heat strip)
C  ←── Blue ─────→  C   (common)

Smart thermostat setup notes:

  • Set O/B to "O" (energize on cooling) for Carrier, Trane, Lennox, Goodman
  • Set O/B to "B" (energize on heating) for Rheem, Ruud
  • If unsure: try "O" first — if heat and cool seem reversed, switch to "B"
  • Aux heat lockout: Set to 40°F in South Florida (prevents expensive heat strip use above 40°F)

Configuration 3: Two-Stage AC

Found in: Larger South Florida homes with variable or two-stage compressors

Thermostat          Air Handler
─────────          ───────────
R  ←── Red ──────→  R   (24V hot)
Y1 ←── Yellow ───→  Y1  (stage 1 compressor)
Y2 ←── Pink ─────→  Y2  (stage 2 compressor)
G  ←── Green ────→  G   (blower)
W  ←── White ────→  W   (heat)
C  ←── Blue ─────→  C   (common)

Notes: Stage 1 runs at ~67% capacity (quieter, more efficient). Stage 2 engages when demand is high. Most smart thermostats support this — configure in Equipment settings.

Configuration 4: Mini-Split (No Thermostat Wire)

Found in: Additions, condos, converted garages

Mini-splits don't use traditional thermostat wiring. They communicate between indoor and outdoor units via proprietary cables. Smart thermostat integration options:

  1. IR Blaster (Sensibo, Cielo, Flair Puck): Mimics the remote control via infrared
  2. Wi-Fi module (manufacturer-specific): Daikin, Mitsubishi, Fujitsu offer their own
  3. Dry contact adapter: Some mini-splits accept a thermostat via dry contact terminals

Troubleshooting Wiring Issues

Thermostat Has Power But AC Won't Start

  1. Check Y wire connection at air handler — loose terminal is the #1 cause
  2. Verify contactor is receiving 24V (multimeter across contactor coil)
  3. Check float switch — clogged condensate drain opens the safety float, breaking the circuit

Blower Runs But No Cooling

  1. Y wire may be disconnected at the air handler or condenser disconnect
  2. Check outdoor unit breaker
  3. Verify condenser contactor is pulling in (24V from Y wire)

Heat Won't Turn Off

  1. W wire may be shorted to R at a junction
  2. Check for damaged cable in attic (rodent damage common in South Florida)
  3. Verify thermostat is calling for cool (Y), not heat (W)

Short Cycling (Turns On/Off Every Few Minutes)

  1. Check for a shorted wire in the cable run
  2. Verify thermostat differential isn't set too small
  3. Check for refrigerant issues (low charge causes high-pressure cutout)

Safety

  • Always turn off power at the breaker before touching any wires
  • Thermostat wires carry 24V AC — low voltage but can damage equipment if shorted
  • If you see 120V or 240V wires near the thermostat location, those are NOT thermostat wires — do not connect them
  • When in doubt, photograph everything and consult a licensed HVAC technician