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How to Troubleshoot and Fix a Coleman-Mach RV Air Conditioner

If your Coleman-Mach RV air conditioner isn't cooling like it used to—or worse, not turning on at all—don’t panic. Many common issues can be diagnosed and fixed without a trip to the service center. In this DIY guide, we’ll walk you through how to troubleshoot and repair a Coleman-Mach AC unit, step by step.

? Common Coleman-Mach AC Problems (and How to Spot Them)

Before we dive in, here are the most common RV AC issues:

? Step-by-Step Troubleshooting Checklist

✅ 1. Check Power Supply

• Make sure your RV is plugged into shore power or your generator is running.

• Use a multimeter to confirm 120V AC is reaching the unit.

• Check your breaker panel—tripped breakers or blown fuses are often the culprit.

Tip: Coleman-Mach ACs require steady power. If voltage drops below 108V, performance suffers or the unit may not run at all.

✅ 2. Inspect the Thermostat

• If the display is dead or unresponsive, check the thermostat fuse or replace batteries (if applicable).

• Inspect wiring between the thermostat and control box for corrosion or looseness.

• Try resetting the thermostat by disconnecting power for a few minutes.

Pro Tip: Upgrade to a digital thermostat for better temperature control and diagnostics.

✅ 3. Examine the Control Board

• The control board (or relay board) is the brain of the system.

• Look for signs of damage like burnt spots, corrosion, or loose connections.

• If you hear clicking but nothing happens, a relay may have failed.

DIY Fix: Replace the control board (we carry OEM replacements at RVACGuys.com) — it's a plug-and-play job for most units.

✅ 4. Clean or Replace the Air Filters

• Dirty filters block airflow and can cause the system to freeze up or shut down.

• Remove filters from the ceiling assembly and wash with warm, soapy water.

• Replace filters if they're cracked, brittle, or permanently clogged.

✅ 5. Inspect the Condenser & Evaporator Coils

• Dirt on the coils restricts airflow and reduces cooling performance.

• Remove the shroud and gently clean the coils with a coil cleaner or compressed air.

Warning: Turn off all power before removing the shroud or touching internal components.

✅ 6. Test the Capacitors

• Weak or failed capacitors are a very common issue.

• Use a multimeter with capacitance testing to check both the start and run capacitors.

• Bulging, leaking, or cracked capacitors should be replaced immediately.

✅ 7. Listen for the Compressor

• If your fan runs but you don’t hear the low hum of the compressor, it may be:

  • Low voltage

  • A bad start capacitor

  • A failed compressor (worst-case scenario)

Try installing a soft start kit to reduce startup load and extend compressor life.

? Final Thoughts: Fix It or Replace It?

If your Coleman-Mach AC unit is over 8–10 years old, or you’ve already replaced key components, it may be time to upgrade. Newer models are quieter, more efficient, and easier to maintain.

Explore our top Coleman-Mach replacement units here.

? Recommended Replacement Parts (Available at RVACGuys.com)

• Coleman-Mach OEM Control Boards

• Start & Run Capacitors

• Replacement Thermostats

• Coleman Air Filters

• Soft Start Kits

✅ Keep Your Cool — The DIY Way

With the right tools and a little know-how, you can handle most Coleman-Mach RV AC issues yourself. Not sure which part you need? Contact us at RVACGuys.com — we’re happy to help troubleshoot or recommend the correct OEM replacement.