RV Air Conditioner Service & Replacement Guide (Dometic / Coleman-Mach)

RV Air Conditioner Service & Replacement Guide (Dometic / Coleman-Mach)

“Drew, my AC just died completely—it was cooling fine yesterday, and now it won’t even turn on. I’m not hearing the compressor hum or anything. Is the whole unit shot?” That’s the call I got from a friend boondocking near Sedona last month, and it’s also the exact moment I realized most RV owners jump straight to the worst-case diagnosis without running through the simple stuff first. Your instinct says compressor failure, so you’re already pricing replacements at $800 or $1,200. But nine times out of ten with a dead-silent unit, the culprit is something sitting on your roof that costs less than a tank fill-up. The real work isn’t throwing money at parts—it’s methodically testing what’s actually broken. With rooftop air conditioners, whether Dometic Brisk II or Coleman-Mach 8, that difference between “doesn’t work” and “here’s why it doesn’t work” can save you a thousand dollars and three days of aggravation. Let me walk you through the exact process I use.

The Capacitor That Stops Your AC From Even Trying to Start

When a capacitor fails on your Dometic rooftop unit, you won’t get a gradual decline in cooling or weak output—you get complete silence. The 60/5 MFD capacitor is what stores the electrical charge needed to spin up the motor itself, and the moment it dies, nothing happens when you flip the thermostat to cooling mode.

Parts and Tools

• Replacement capacitor matched to the microfarad and voltage rating stamped on the old one (typically 60/5 MFD for Dometic rooftop units) — check current price
• Needle-nose pliers or small wire strippers for disconnecting capacitor terminals
• Multimeter with capacitance setting to test the old capacitor before removal
• Insulated screwdriver set (Phillips and flathead) for accessing the AC shroud and terminal connections
• Masking tape and permanent marker for labeling wire positions before disconnection
• Safety glasses and work gloves for rooftop work

Step-by-Step Instructions

Step 1: Kill power to the AC unit at the breaker

Locate your RV’s main electrical panel and switch off the 120V breaker feeding the air conditioner. Wait 60 seconds to allow any residual charge to bleed from the capacitor. Even with power off, a failed capacitor can still hold a charge—treat it as live until you’ve discharged it. This step prevents shock and protects your multimeter.

Step 2: Access the rooftop unit and photograph the wiring

Climb onto the roof with your multimeter and camera. Locate the AC shroud—usually a plastic or aluminum cover held by four to six screws around the perimeter. Before removing anything, photograph the capacitor terminals and their wire connections from multiple angles. Note which wire connects to which terminal. This photo is your insurance against reassembling it wrong.

Step 3: Test the capacitor with a multimeter

Set your multimeter to capacitance mode. Touch the probes to the capacitor terminals. A good 60/5 MFD capacitor should read between 55 and 65 microfarads on the 60 side. If it reads zero, reads infinity, or the meter won’t stabilize, the capacitor is dead. If it reads in spec, the problem is elsewhere—stop here and investigate the thermostat, breaker, or contactor instead.

Step 4: Discharge the capacitor safely

Even with the breaker off, discharge any remaining voltage by touching an insulated screwdriver across both terminals simultaneously. You may see a small spark—this is normal and confirms the capacitor held charge. This prevents a shock when you grab the terminals with your bare hands during removal.

Step 5: Remove the old capacitor and label the wires

Using needle-nose pliers, gently pull each wire terminal off the capacitor posts. As you disconnect each wire, immediately wrap a small piece of masking tape around it and write the terminal it came from (C, FAN, HERM, or RUN). Capacitors are directional on some models—your labels prevent a reversed installation that won’t start the motor.

Step 6: Install the new capacitor and reconnect wires

Slide the new capacitor into the mounting bracket, ensuring it sits flush and level. Reconnect each wire to its original terminal using your tape labels as a guide. Push the spade connectors firmly onto the posts until they click or seat fully. Tug each wire gently to confirm it won’t slip off during operation.

Step 7: Reassemble the shroud and test the unit

Replace the plastic shroud and tighten all screws evenly. Climb down from the roof, return to your breaker panel, and switch the AC breaker back on. Set your thermostat to cooling mode and listen for the compressor hum within 10 seconds. Feel the air coming from the vents—it should turn cold within 2 to 3 minutes. If the compressor hums but no cold air flows, the capacitor swap worked but a separate issue (refrigerant, airflow) exists.

What works

• You’ll know immediately after swapping it in—compressor hums, fan spins, cold air flows. No waiting for a gradual restart or mysterious reset cycles.
• Your amperage draw snaps to normal the instant you engage the thermostat, so anyone pulling shore power will see the load spike right away and know the system is running properly.
• A replacement capacitor runs you around $25 instead of the $800–$1,200 you’d spend on a compressor swap you never actually needed.

What doesn’t

• You’ve got to pull out a multimeter and test the old capacitor’s actual condition before you order a replacement—guessing on specs means you end up with something that either won’t fit or fails the moment it draws real current.
• Aftermarket capacitors sometimes ship with terminal crimps that aren’t quite seated tight enough, so you need to double-check the connection is solid before you button everything back up or you’ll end up chasing intermittent start failures.

I second-guessed swapping just the capacitor on a 2015 Dometic unit because the owner had already convinced himself the compressor was seized, but the moment that new capacitor went in and the motor hummed to life, it was clear nothing else was wrong. Order the Fits for Dometic 3312195.000 Air Conditioner RV AC Motor Capacitor 60/5 MFD, Heavy Duty Air Conditioner Capacitor Replacement, Compatible with Dometic 3312195000 RV Air Conditioner Models and test it before you touch anything else.