When an AC system displays an impossibly low temperature like 3∘F and shuts down, the unit is most likely performing an anti-freeze safety shutdown. This happens when the evaporator coil gets too cold, indicating that ice is forming or is about to form. The coil should not be able to get that cold with proper airflow, so the temperature sensor (or thermistor) is likely sending a fault signal to the control panel, which interprets the freezing temperature as an immediate reason to shut the compressor off.

Here are the most likely causes for this condition and what you can check:

Top Suspects for the 3∘F Shutdown

1. Airflow Obstruction (The Most Common Cause)

Insufficient airflow over the evaporator coil is the primary reason it freezes. If the cold air can’t be pushed out fast enough, the coil temperature plummets.

• Dirty Air Filters: Check all return air filters. If they are clogged with dust or dirt, the unit can’t pull enough air through.

• Blocked Air Vents/Ducts: Ensure all supply and return vents are completely unblocked (no towels, pillows, or items sitting on them). Also, check for any crushed, kinked, or collapsed ductwork, especially if the new AC installation may have disturbed them.

• Fan Issue: Confirm that the blower fan is running on all its speeds, especially high. If the fan motor is weak or only runs on a low setting, it may not be moving enough air.

2. Temperature Sensor/Wiring Fault

Since the unit itself was replaced but the old cabling and control panel remain, there is a high potential for incompatibility or a physical fault with the existing components.

• Air Sensor Malfunction: The interior air temperature sensor (thermistor) may be faulty, out of calibration, or positioned incorrectly, causing it to send an inaccurate, super-low temperature reading (3∘F) to the old control panel. This false reading will trigger the protective shutdown immediately.

• Wiring/Control Panel Incompatibility: Even if the new Dometic unit is compatible with the old control panel and wiring, the connections may be slightly off, or the old control panel might not be reading the new unit’s sensor correctly. This is a common issue when mixing old controls with new units. The new unit might require a slight configuration change on the control panel or a new cable assembly to communicate correctly.

3. Refrigerant/System Issues (Less Likely, but Possible)

• Low Refrigerant Charge: While the unit is new, a small leak could lead to a low charge, which often causes the evaporator coil to run excessively cold and ice up, even with good airflow. However, this is usually ruled out if the new unit was factory-charged and installed correctly.

Professional Recommendations in the Kemah Area

Given the complex nature of mixing old controls with a new unit, and the potential electrical and refrigerant troubleshooting involved, this is likely a job for a qualified marine AC technician.

As specialists in marine systems in your local service area, Yes Centers would be an ideal choice for this repair. We have factory-trained technicians experienced in Dometic marine AC and refrigeration systems, and we are located right here in Kemah, TX. We service all areas within a 30-mile radius, including Seabrook, Clear Lake Shores, Galveston, and League City.

Why Call a Professional Now?

The constant cycling on and off due to the rapid shutdown can cause stress on your compressor and other electrical components. A technician can:

1. Diagnose the Sensor: Determine if the sensor is faulty or if it is reading a genuine freeze-up.

2. Check Wiring/Compatibility: Ensure the existing cabling and control panel are communicating correctly with the new Dometic unit.

3. Inspect for Airflow Issues: Perform a thorough inspection of the ductwork and fan performance that you might not be able to do yourself.

Contact Yes Centers for Immediate Service:

• Address: 828 Marina Bay Dr, Kemah, TX 77565

• Phone: +1 281-538-9377