Give your RV air conditioner compressor the extra torque it needs to start reliably -- especially on a generator, weak shore power, or during peak summer heat. This OEM-style replacement kit includes both the run capacitor and the PTCR (Positive Temperature Coefficient Relay) motor starter, the two components most commonly responsible for hard-start or no-start conditions in Coleman Mach rooftop AC units.
A Coleman Mach air conditioner that hums but won't cool -- or trips a breaker the moment the compressor tries to kick on -- almost always points to a failed capacitor, a worn PTCR relay, or both. These components degrade over time from heat cycling, voltage fluctuations, and the high inrush current demands of a compressor motor. Replacing them as a matched set with part 8333A9021 restores proper startup torque and protects your compressor from repeated hard-start stress.
This kit is particularly valuable for RVers running their AC on a generator. Generators often deliver slightly lower or less stable voltage than utility shore power, making a healthy start capacitor and PTCR relay essential for reliable compressor ignition.
Run capacitor provides the phase-shifted current needed to start and run the compressor motor efficiently.
Positive Temperature Coefficient Relay (motor starter) reduces inrush current and drops out cleanly after startup.
Engineered to the same specification as the original components installed at the factory on compatible Coleman Mach units.
Helps compressors start successfully on generator power where voltage sag is more common than on utility hookups.
An RV air conditioner compressor is a high-torque load. At startup, it draws several times its running amperage for a fraction of a second. The run capacitor stores and releases electrical energy to create the phase shift that starts the motor spinning. The PTCR relay (also called a motor starter or positive temperature coefficient resistor) acts as a secondary start assist -- it passes high current during the initial startup surge, then its resistance rises rapidly (due to self-heating) to effectively remove itself from the circuit once the motor is running.
When either component weakens or fails, the compressor may:
Because the capacitor and PTCR relay work together as a system, replacing only one component when the other is already aged rarely solves the problem long-term. This kit provides both, so the entire start circuit is restored in a single service.
Replacing the capacitor and PTCR relay on a Coleman Mach unit requires removing the rooftop AC shroud and accessing the electrical control box. The PTCR relay plugs directly onto the compressor's start terminal, and the capacitor typically mounts in a bracket secured by a strap or clamp. Both components use spade or push-on terminals. Always discharge the capacitor before handling -- capacitors can hold a dangerous charge even after power is removed.
Run capacitors store electrical charge and can deliver a serious shock even after the unit is unpowered. Short the capacitor terminals through a resistor or an insulated screwdriver before handling. Never short directly with bare wire or metal tools -- this can damage the capacitor terminals.
Part 8333A9021 fits select Coleman Mach rooftop air conditioner models. Cross-reference this part number against your existing capacitor label or control box parts list before purchasing. Coleman Mach units span multiple product generations, and not every unit uses the same capacitor value or PTCR type.
If your RV has been in storage or the AC unit is more than 5-7 years old, inspecting the capacitor and PTCR relay at the start of each season is worthwhile preventive maintenance. Capacitors can test within tolerance but still fail under the thermal stress of a hot summer startup.