Diagnosing A/C Systems : Flooded Start

 Overview:

• Crankcase heaters are used in air conditioning systems to prevent refrigerant migration into the compressor's oil during the off-cycle, which can cause damage when the compressor starts up. This lesson covers the purpose of crankcase heaters, different types, wiring options, and how to check for proper operation.

Purpose of Crankcase Heaters:

• Prevent Refrigerant Migration: The primary purpose of a crankcase heater is to keep the compressor oil warm, preventing refrigerant from condensing in the crankcase during the off-cycle.
• Protect Compressor: By keeping the oil warm, the crankcase heater ensures that the compressor is protected from potential damage caused by liquid refrigerant mixing with the oil.

Types of Crankcase Heaters:

1. External Crankcase Heaters:

   • Description: Mounted externally around the compressor.
   • Function: Provides heat directly to the crankcase by warming the outer surface of the compressor.

2. Internal Crankcase Heaters:

   • Description: Installed inside the compressor.
   • Function: Heats the oil and refrigerant internally, often using the compressor’s windings.

Wiring Options for Crankcase Heaters:

1. Constant Operation:

   • Description: Some crankcase heaters are wired to stay on continuously, providing a small amount of trickle current to the compressor motor windings during the off-cycle to generate heat.
   • Advantage: Ensures that the oil is always warm, reducing the risk of refrigerant migration.

2. Ambient Thermostat-Controlled:

   • Description: Wired to line voltage but controlled by an ambient thermostat that cycles the heater on and off based on outdoor temperature.
   • Typical Setting: The thermostat turns the crankcase heater on when the outdoor temperature falls below 50-60°F.
   • Advantage: More energy-efficient, as the heater only operates when necessary.

Checking Proper Operation of a Crankcase Heater:

1. Voltage Check:

   • Procedure: With the system powered on, check for voltage at the crankcase heater terminals.
   • Interpretation:
     • Voltage Present: The heater should be operational; if it’s not heating, there may be a problem with the heater itself.
     • No Voltage: Indicates a potential issue with the contactor, thermostat, or source voltage.

2. Resistance Check:

   • Procedure: Turn off the power, isolate the crankcase heater by disconnecting one side of the wires, and measure resistance across the heater.
   • Interpretation:
     • Measurable Resistance: Indicates that the crankcase heater is intact and should function properly.
     • Infinite Resistance (OL): Indicates an open circuit, meaning the heater is faulty and needs to be replaced.

Common Issues and Diagnosis:

• No Heat: If the crankcase heater is not providing heat, it could be due to a lack of power supply, a faulty thermostat, or a failed heater.
• Checking Wiring and Components: If voltage is not present at the heater, check the contactor and source voltage. If voltage is present but the heater is not working, test for resistance to confirm if the heater is faulty.

Conclusion:

• Regularly checking the crankcase heater is essential for maintaining the health of the compressor. Proper diagnosis involves checking for voltage and resistance to ensure the heater is functioning correctly. This helps prevent potential compressor damage due to refrigerant migration, especially in colder environments.