A rooftop Air Conditioner may look ready to run from the outside, yet an electrical problem can be developing inside its compressor. During this Air Conditioning repair project in Las Vegas, Fast Affordable Air inspected a Rheem rooftop package unit and tested the electrical condition of its LG compressor.
The most important finding came from an M500 megohmmeter. The meter showed a reading in the red “Bad” range. This indicated that the electrical insulation inside the compressor was severely weakened. Accurate testing helped identify the real problem and reduced the chance of replacing unrelated parts that would not restore dependable Cooling.
Fast Affordable Air is a licensed HVAC contractor serving Las Vegas, Henderson, North Las Vegas, and surrounding communities in Clark County. Similar diagnostic services are explained on the company’s Las Vegas AC repair page.
Inspecting the Rheem Rooftop Package Unit
The first photos show the complete Rheem Heating and Cooling unit installed on a flat roof. This is called a package unit because the major heating and cooling parts are housed inside one large outdoor cabinet. A traditional split system has separate indoor and outdoor equipment.
Rooftop equipment faces direct sunlight, wind, dust, rain, and intense roof temperatures. Las Vegas heat can make the roof much hotter than the surrounding air. That extra heat places more stress on the compressor and other electrical parts.
The technician inspected the cabinet, outdoor coil, roof mounting area, conduit, refrigerant tubing, and access panels. Conduit is the protective tube that shields electrical wires from sunlight, sharp metal, and weather. The area around the unit was also checked to make sure technicians could safely reach its service components.
Opening the HVAC Cabinet
The next photo shows the package unit with its service panels removed. Opening these panels provided access to the compressor, electrical compartment, refrigerant lines, blower section, and control wiring.
The compressor is often described as the heart of an AC system. It moves refrigerant through the Cooling circuit. Refrigerant is a special fluid that collects heat from the indoor air and carries that heat outdoors. If the compressor cannot start or operate safely, the central Air Conditioner cannot provide dependable cooling.
The technician looked for damaged wires, burned connections, loose terminals, oil marks, rust, and signs of overheating. These visual checks are important, but a compressor can have internal electrical damage without showing an obvious problem on the outside.
Checking the Electrical Disconnect and Fuses
Another photo shows the open electrical disconnect mounted on the package unit. The disconnect is a safety switch that allows electrical power to be shut off near the equipment. This helps protect the technician while the Air Conditioning system is being inspected.
The disconnect contains two cartridge fuses. A fuse is a safety device that stops the flow of electricity when the current becomes too high. The technician inspected the fuses, terminals, and wiring for heat damage and loose connections.
A failed fuse can stop an AC from running, but replacing a fuse without finding the cause may only lead to another failure. A compressor with damaged internal insulation may pull excessive power, trip a breaker, or cause a fuse to open. That is why the compressor needed a separate electrical test.
Inspecting the LG Compressor Connections
A close-up photo shows the LG compressor and its three electrical terminals. These connections are commonly identified as start, run, and common. They provide power to the motor windings inside the compressor.
A winding is a coil of insulated copper wire that helps create the magnetic force needed to run the motor. The insulation around these wires should stop electricity from leaking into the metal compressor shell.
The technician isolated the compressor connections before testing. This helps prevent other wires and controls from affecting the reading. The terminals and wire ends were also checked for corrosion, looseness, and heat damage.
Testing Compressor Insulation With an M500 Megohmmeter
The last two photos show an M500 megohmmeter being used at the compressor. A megohmmeter, sometimes called a megger, measures electrical insulation resistance in megohms.
Think of insulation as the plastic coating around an extension cord. It keeps electricity inside the wire. If that coating becomes weak, electricity can leak where it does not belong. Inside a compressor, damaged winding insulation may allow electricity to travel toward the metal shell. Technicians call this a short to ground.
The M500 displayed a reading below 20 megohms in its red “Bad” range. This is a serious warning that the compressor’s winding insulation is no longer providing strong electrical protection. Heat, age, moisture, acid inside the refrigerant circuit, or years of electrical stress can contribute to this condition.
The reading should be compared with resistance, voltage, amperage, terminal condition, and manufacturer information. Amperage is the amount of electrical current a component uses. These additional checks help confirm whether the compressor has failed and whether compressor replacement or complete rooftop-unit replacement is the better choice.
Why Accurate Compressor Diagnosis Matters
A weak or grounded compressor may cause several problems:
- The Air Conditioner may not start.
- A breaker or fuse may repeatedly trip.
- The compressor may start and then shut down.
- The HVAC system may run without producing enough cold air.
- Electrical parts may overheat.
- Energy may be wasted during failed starting attempts.
Finding the electrical problem before installing capacitors, contactors, or other unrelated parts helps avoid wasted repair costs. It also protects the rest of the Central Air Conditioning system from repeated electrical stress.
Once the failed compressor or package unit is correctly replaced, the Cooling system can be tested for proper voltage, refrigerant charge, airflow, and temperature change. Correct operation can provide steadier indoor comfort, safer performance, and better energy use. Information about preventing developing problems can also be found on the Fast Affordable Air maintenance page.
Project Summary
- Inspected a Rheem rooftop package HVAC unit in Las Vegas
- Opened the cabinet and examined the internal components
- Checked the electrical disconnect, cartridge fuses, and wiring
- Inspected the LG compressor and its electrical terminals
- Isolated the compressor for insulation testing
- Tested the windings with an M500 megohmmeter
- Found a reading below 20 megohms in the red “Bad” range
- Identified serious compressor insulation weakness requiring further repair or replacement evaluation