MLK Weekend Cold Snap in Summerdale: Heat Pump Defrost 101

Right now, before MLK weekend, walk to your outdoor heat pump unit. Look at the coil. If you see ice forming on the bottom third, that's normal. If you see solid ice across the top of the unit, you have a problem. Here's how to tell the difference.

This post is direct instructions, in order. Read it, then go outside. Each section starts with what to do and what to look for. MLK weekend in Summerdale typically delivers the first sustained sub-35°F stretch of the year, and that's the test most heat pumps either pass or fail. The single-stage equipment standard in Highland Park, Lake Osprey, Summerdale Heights, and Caldwell Farms is particularly vulnerable to defrost issues because the systems were rarely tested below 40°F during commissioning.

Step 1 — Find your outdoor unit and inspect the coil

Walk outside. The outdoor unit is the big metal box, usually on a concrete pad near the garage or the side of the house. Look at the vertical fins (the coil) on the sides and back of the unit. They should be clean, mostly free of leaves and debris, and roughly the same color all the way around.

In normal operation during a cold snap below 40°F, you should see:

• Light frost or thin ice on the bottom one-third of the coil
• Some moisture or condensation on the cabinet
• Steam or vapor when a defrost cycle is running (good sign — that's the system working)

You should not see:

• Solid ice across the top of the coil
• Ice bridging between the coil and the fan grille
• Ice on the fan blades themselves
• A coil that's completely encased in white frost from top to bottom

If the coil looks bad, skip ahead to Step 6. If it looks normal, keep going.

Step 2 — Listen for the reversing valve

Stand next to the unit for two or three minutes. Wait for the system to start a defrost cycle (it'll happen within 30-90 minutes if outdoor temp is below 40°F). When defrost starts, you'll hear a distinct "whoosh" or "click" sound from inside the cabinet — that's the reversing valve switching the system into temporary cooling mode so the outdoor coil heats up and melts ice.

Listen for:

• A clean, single click or whoosh at defrost start
• A second click 5-10 minutes later when defrost ends
• Steady fan operation through the cycle (the outdoor fan stops running during defrost on most units, restarts after)

Listen against:

• Repeated clicking every few seconds (the contactor or reversing valve solenoid is failing)
• A grinding or scraping sound (fan blade hitting ice, or a bearing problem)
• A humming sound that doesn't resolve into normal operation (motor stalled)

Note any unusual sound and the time. Move to step 3.

Step 3 — Check supply air temperature inside

Walk back inside. Find a supply register near the air handler — usually a hallway or living room vent. Hold your hand 6 inches below it for 30 seconds while the system is running.

Normal supply temperatures with outdoor in the low 30s°F:

• Heat pump alone: 90-100°F at the register (warm but not hot)
• With aux heat engaged: 110-130°F (noticeably hot)
• During defrost: drops to 60-70°F for 5-10 minutes (this is normal — uncomfortable but expected)

If you have a thermometer, use it. A meat probe thermometer or any digital cooking thermometer works fine. Stick it in the register slot, wait 60 seconds, read.

Bad signs:

• Supply temperature consistently below 85°F when system is running and outdoor is 30°F+ — heat pump is undercharged or the coil is partially frozen
• Supply temperature drops below 50°F during defrost and stays there for more than 12 minutes — defrost cycle is malfunctioning or aux heat isn't engaging during defrost
• Supply temperature feels cold (under indoor room temp) while system runs — system is stuck in cooling mode, turn off immediately

Step 4 — Watch one full defrost cycle

Set a timer. Stay with the outdoor unit (or watch from a window) for 90 minutes if needed, until you see one complete defrost cycle.

Time the cycle:

• Start: reversing valve clicks, outdoor fan stops, vapor begins rising from the coil
• Middle: ice visibly melts off the coil; you can see water dripping or running off the bottom
• End: reversing valve clicks again, outdoor fan resumes, normal heating operation returns

A healthy defrost cycle clears all visible ice off the coil within 6-10 minutes total. If the cycle ends and significant ice remains on the coil, the defrost board is terminating the cycle before it's complete — common cause is a failed defrost sensor (the small disk-shaped sensor mounted to the coil that tells the board when the coil is warm enough to end defrost). That's a heating repair call, not a homeowner fix.

If you don't see a defrost cycle in 90 minutes and the outdoor temp is below 40°F, the defrost initiation circuit isn't working. The system is running entirely on heat pump mode against a coil that's accumulating ice — eventually the system will either fail outright or freeze the coil completely.

Step 5 — Check the area around the unit

Look at the ground around the heat pump.

You should see:

• Wet concrete or wet ground from defrost runoff
• Maybe some ice on the pad or the ground if temperatures have been below freezing for an extended period
• Clear airflow above and around the unit

You should not see:

• Standing water or ice damming around the unit base (means the drain isn't clearing — common on units installed too low to grade)
• Snow or leaves piled up against the coil
• Anything stored or stacked within 24 inches of the unit on any side
• A tarp or cover on the unit (covers belong on units in storage, not running units)

Clear anything blocking airflow. The Foley service area notes cover similar inspection points for the slightly different equipment mix south of Summerdale; the Gulf Shores guide discusses why coastal units have additional considerations during winter operation.

Step 6 — If the coil is iced, do this

Stop. Don't try to clear ice manually with a hammer or screwdriver — you'll puncture the coil and turn a manageable service call into a major coil replacement.

Do this in order:

1. Go inside. Switch the thermostat from HEAT to EM HEAT (emergency heat). On most modern thermostats this is a button or menu option labeled "Emergency Heat" or "Aux Only." This shuts down the outdoor unit completely and runs the indoor electric heat strips.
2. Wait. Let the outdoor coil thaw naturally. With the system off and ambient temperature above freezing during the day, most ice clears in 2-4 hours. If outdoor temp stays below freezing, ice may not clear until the next warmer day.
3. Once ice has cleared, do not switch back to HEAT mode. The reason the coil iced is probably still present (failed defrost sensor, low refrigerant charge, defrost board issue). Running the system again in heat mode will produce the same result.
4. Call us. The service fee is $79; we'll diagnose the issue and quote the repair before any work begins.

Step 7 — If you have a Summerdale single-stage heat pump and outdoor will be below 32°F

Most heat pumps in Summerdale subdivisions like Highland Park and Lake Osprey are single-stage units sized for the original builder spec. They work fine down to about 35°F outdoor. Below that, the system runs continuously (almost no off-cycle), the auxiliary heat strips engage to make up the gap between heat pump output and demand, and the duty cycle stresses everything in the unit.

For MLK weekend with overnight lows forecast to drop to 28-32°F:

• Set a single steady setpoint. Don't run a nighttime setback below 65°F — the recovery from a 60°F setback to 70°F at 7 AM with outdoor at 28°F means the aux strips run for 90+ minutes straight, which costs more than just holding the steady setpoint overnight would have.
• Lock smart thermostat to 65-72°F. Same logic as the Loxley Thanksgiving post — you don't want a houseguest pushing the setpoint to 75°F and running aux for six hours.
• Replace the filter before MLK weekend. Restricted airflow during continuous operation is what causes high-limit lockout on heat strips.
• If you have any reason to think the system is marginal — odd noises this fall, longer-than-usual run times last week, a recent power-cycling issue — get a tune-up before Friday. Cold-snap weekends fill the schedule fast, so call early if anything feels off.

Step 8 — Plan for the worst case

If the system fails completely Saturday or Sunday of MLK weekend with outdoor temperatures in the 20s, here's what to expect:

• Call comes in to 251-383-HVAC. Emergency calls are answered 8am-8pm every day, including Saturdays at no extra charge.
• On-site diagnostic typically 30-45 minutes for a no-heat call. Most common findings: dead capacitor, failed contactor, locked-out defrost board, refrigerant leak.
• We'll diagnose the issue and provide a written repair quote before any work begins. Free second opinions on quoted repairs.
• For a 12+ year old system that fails completely during a cold snap, replacement math gets walked through on the same visit. The Orange Beach service overview and emergency HVAC page both detail how those decisions get made on site.

In the meantime, before the tech arrives:

• Switch to EM HEAT to keep the house warm with electric strips
• Close interior doors to rooms that aren't being used
• Use space heaters in occupied bedrooms (only on circuits not shared with major appliances)
• Don't run the oven for heat — gas ovens vent CO into a closed kitchen

Step 9 — After the cold snap clears

Tuesday after MLK weekend, walk back to the unit. Check the coil for any ice that didn't clear, any unusual debris, any water staining on the cabinet that suggests a refrigerant leak (oily residue near the service ports). Schedule a spring tune-up if you don't already have one on the calendar.

In my 13 years working Baldwin County HVAC, the pattern is consistent: systems that survive MLK weekend without an emergency call usually run fine through the rest of winter. Systems that have a borderline issue during MLK often produce a follow-up failure when a second cold snap hits. The Summerdale service overview walks through the full inland-Baldwin maintenance schedule.

Heat pump defrost is well-engineered when it works. Most of the failure modes are old sensors, old capacitors, and refrigerant charge that's drifted. None of them are difficult to fix when caught before the system is fully iced. Walking outside today, before the cold snap arrives, is the single highest-leverage thing you can do.