How much does a defrost board cost?
$389–$589 installed in San Antonio. The board itself is $120–$280; the rest is diagnosis and labor. Almost always pays for itself within one winter just on the auxiliary heat electric bill savings.
San Antonio · Heat Pump Defrost Board Replacement Repair · Family-Owned Since 1996
Heat Pump Iced Over And Won't Defrost? It's The Defrost Board.
In winter, your outdoor heat pump unit needs to periodically reverse and melt ice off the coil. The defrost board manages that cycle. When it fails, the unit ices up solid and your auxiliary electric heat strips run nonstop.
Typical price
$389–$589
Time to fix
60–90 minutes
Urgency
High in winter — auxiliary heat burns electricity 3x faster
In plain English — what's going on with your heat pump defrost board replacement
When a heat pump runs in heat mode, the outdoor coil is the cold side — and on damp 35–40°F mornings, condensation freezes on that coil. Heat pumps have a built-in defrost cycle: every 30–90 minutes, the defrost board switches the system to cooling mode briefly (with the outdoor fan off) so the hot refrigerant melts the ice. Once a temperature or time threshold is met, it switches back to heating.
When the defrost board fails, the cycle never triggers. Ice builds up on the outdoor coil until airflow is completely blocked, the heat pump can't extract any heat, and your thermostat falls back on auxiliary electric strip heat. Your electric bill triples and your house still feels cold.
Replacement is $389–$589 installed. The board is $120–$280 depending on brand. We diagnose by watching the defrost cycle (or attempting to force it manually), checking the defrost thermostat sensor, and metering board outputs.
What it costs in San Antonio
$389–$589 — Includes new defrost board, sensor inspection, and full heat-pump cycle test. Our $59 diagnostic is waived when you approve the repair, so you only pay for the fix itself.
Symptoms you'll notice at home
If two or more of these sound familiar, it's probably your heat pump defrost board replacement.
Outdoor heat pump coil covered in solid ice
Heat pump runs constantly but house won't warm up
Electric bill spiked in December/January (aux heat running constantly)
Auxiliary heat indicator on thermostat is always lit
Defrost cycle never seems to kick in
Outdoor unit makes weird ice-cracking sounds
Why heat pump defrost board replacements fail in San Antonio
- Failed defrost timer/controller chip on the board.
- Defrost thermostat sensor on the coil failed (board never gets the 'ice' signal).
- Voltage surge from a storm.
- Aging board components (capacitors degrade over years).
- Mice nesting on the board (yes really — common in outdoor units).
How we diagnose and replace it
Here's exactly what a Carnes and Sons tech does at your house — no mystery, no upselling.
- 1
Force a defrost cycle manually
Most defrost boards have test pins that let us trigger a defrost on demand. If the system doesn't reverse and melt ice, the board is bad.
- 2
Test the defrost thermostat
The sensor on the coil tells the board when ice has formed. If the sensor is open or shorted, the board never sees the 'ice' signal even if the board itself works.
- 3
Verify all board outputs
Meter the reversing valve solenoid signal, fan signal, and W2 (aux heat) outputs during a simulated defrost call. Anything that doesn't fire means the board is bad.
- 4
Replace board and verify full cycle
Install matched OEM board, set dip switches/jumpers for your system. Wait for natural defrost or force one — confirm the cycle completes normally and house starts warming.
What Your Neighbors Are Saying
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Heat Pump Defrost Board Replacement questions San Antonio homeowners actually ask
Why is my heat pump iced over?
Either the defrost board failed (never triggers the cycle), the defrost sensor failed (board never sees the ice), or low refrigerant is freezing the coil even with a working defrost cycle. We diagnose to find which one.
Can I melt the ice with a hose?
Don't use hot water — thermal shock cracks the coil. Cold water from a garden hose will eventually melt it, but the ice will just come back in a few hours if the underlying problem isn't fixed. Better to turn the system to 'emergency heat' (which locks out the heat pump and runs only aux strips) until we get there.
Will the new board come with a warranty?
Yes — 1 year minimum parts warranty from us, often 2–5 years from the manufacturer. We'll always check if your system is still under manufacturer coverage.
Could it be something else?
Yes — failed reversing valve, low refrigerant, weak compressor, or bad outdoor fan can all cause symptoms that look like a bad defrost board. We test before condemning. A real diagnostic costs $59; throwing a $400 board at it without testing is gambling.
How long does a defrost board last?
10–15 years on average. Surge damage and outdoor temperature swings shorten that. A surge protector can add years.
Why is my electric bill so high in winter?
Aux heat is electric resistance heating — about 3x more expensive to run than the heat pump itself. When your defrost board is broken, the heat pump can't keep up, the aux strips run constantly, and your bill triples. Fixing the defrost board usually pays for itself in 1–2 months of bill savings.
Do you carry the board on the truck?
We carry common brands (Carrier/Goodman/Rheem). Proprietary or older boards we may need to order — usually same-day or next-day. We'll tell you up front.
Serving heat pump defrost board replacement repairs across the greater San Antonio area
We're based in Stone Oak and roll trucks across San Antonio and the surrounding Hill Country every day.
Carnes and Sons Air Conditioning
License TACLB29435E · Family-Owned Since 1996
401 E Sonterra Blvd Suite 375
San Antonio, TX 78258(210) 600-5091
San Antonio, TX 78258(210) 600-5091
Mon–Sat: 7AM – 8PM · Emergency same-day service
Cities & neighborhoods we serve
San Antonio · Stone Oak · Alamo Heights · Hollywood Park · Hill Country Village · Shavano Park · Castle Hills · Leon Valley · Helotes · Boerne · Fair Oaks Ranch · Bulverde · Timberwood Park · Garden Ridge · Schertz · Cibolo · Selma · Universal City · Live Oak · Converse · Windcrest · New Braunfels
Talk to a real person about your heat pump defrost board replacement
No call center. The owner or one of his sons picks up.
(210) 600-5091