Coleman Mach RV Air Conditioner Not Cooling: Fix Every Failure

Check the Breaker First

' Both must be fully on. If either has tripped to the middle position, reset it by pushing it fully off first, then fully on. If it trips again immediately when the AC tries to start, you have an overcurrent condition — usually a seized compressor or a badly failed capacitor drawing too much current.

Do not keep resetting a breaker that immediately trips. That's the breaker protecting you from a short or a locked motor. If the breaker holds and the AC still doesn't respond, check the wall thermostat — confirm it's set to COOL, the setpoint is below room temperature, and the fan is on.

Then check that the thermostat wires haven't come loose at the wall plate (unscrew it and confirm all wires are seated).

Diagnose and Replace the Run Capacitor

The run capacitor is responsible for starting and running both the compressor and the fan motors. When it fails, the motor hums but can't overcome the startup resistance — you hear a clicking or buzzing sound, then the unit shuts off on thermal overload. Safety first: disconnect power at the breaker before touching the capacitor.

Even with power off, capacitors store charge — a fully charged RV run capacitor stores enough energy to cause a serious electrical shock. Use a screwdriver with a fully insulated handle and grip only the insulated portion — do not touch any metal part of the tool during discharge. Touch the blade across both terminals simultaneously.

You will hear a loud snap and may see a small arc — this is expected and normal. Keep your grip firm on the insulated handle throughout. After discharging, verify with a multimeter that voltage across the terminals reads zero before handling the capacitor.

Access: remove the rooftop shroud (4–6 screws around the perimeter, plastic or metal cover). The capacitor is cylindrical, silver or black, positioned near the compressor. Look for a swollen or bulging top, leaking dark oil, or a burnt smell — these confirm failure.

To test with a multimeter in capacitance mode: Coleman Mach units typically use a 35/5 µF dual-run capacitor. A reading below 90% of the rated value means replace. Replacement: match the µF rating exactly (35/5 µF).

Voltage rating of 370V or 440V are both fine — higher is acceptable. Cost is $15–35 from any HVAC supply. Reconnect terminals to the exact same positions: HERM goes to the compressor, FAN goes to the fan motor, COM goes to the common wire from the contactor.

Clean the Air Filter and Condenser Coils

A clogged air filter and dirty condenser coils together reduce cooling efficiency by 20–40% and can cause the compressor to overheat and trip its internal thermal protector, resulting in a unit that starts, runs briefly, then shuts off. The filter is inside the ceiling assembly directly below the rooftop unit — push the tabs on the plastic shroud and lower it to access the foam or mesh filter panel. Rinse under running water until clean.

Allow to completely dry before reinstalling — a wet filter restricts airflow. If the filter is torn or won't clean up, replace it ($8–15). For the condenser coils (rooftop, surrounding the compressor): remove the rooftop shroud, brush loose debris off the fins with a soft brush, spray no-rinse coil cleaner foam across the fins, wait 5 minutes, and rinse gently from the inside out with a garden hose.

Never use a pressure washer — it bends the aluminum fins and reduces airflow permanently. Straighten any bent fins with a fin comb. Perform coil cleaning once per season before the first hot-weather use.

Test the Fan Motor

Coleman Mach units have two fan motors: the evaporator blower (inside the ceiling assembly, circulates cooled air into the RV) and the condenser fan (rooftop, exhausts heat from the coils). A failing motor causes airflow problems, reduced cooling, and eventual compressor overheating. Signs of fan motor failure: grinding or squealing sound, the fan blade turns slowly or not at all, the unit clicks on and runs but airflow is noticeably weak, or the motor starts but stops after a few minutes.

Quick test: with power off, try to spin the fan blade by hand. It should spin freely with almost no resistance. Stiff or seized = failed bearings.

Listen during operation: a motor drawing extra current because of bad bearings often makes a low hum distinct from normal operation. Coleman Mach evaporator blower motors run $45–90. The condenser/fan motor is $80–150.

Match your model number from the data plate on the rooftop unit before ordering. Fan motor replacement requires rewiring the new motor to the same terminals and securing the fan blade to the shaft at the same depth.