Forest River Impression – AC Capacitor & Fan Motor Service

Last summer, I found myself facing a hefty dealership quote of $380 just to diagnose and replace the AC capacitor on my Forest River Impression. With labor costs at $220 and parts around $45, I realized that I had to close the gap between what a shop charges and what I actually needed to spend. After traveling over 80,000 miles across North America in three different rigs, I’ve learned a thing or two about DIY repairs. When your rooftop unit starts that annoying hum without firing up, or the fan gives out during the sweltering heat of July, you’re left with two choices: shell out nearly four hundred dollars for a service call or spend just forty minutes with a wrench and a $25 component. The run capacitor and fan motor on these Forest River units have a predictable failure pattern, making both repairs well within the DIY realm once you know the signs to look for. This guide will take you through the diagnostic process, the exact steps for swapping out the parts, and the crucial safety precautions to avoid a shocking experience—because a charged capacitor doesn’t care if you’re trying to help yourself.

Why That Dual Run Capacitor Matters More Than You’d Think

The performance of your Forest River’s rooftop AC hinges on a component that most owners only become aware of when it quits: the dual run capacitor. This little piece is the electrical relay that tells your compressor and fan motor to kick in. When it starts to fail, you’ll notice the familiar hum (indicating the motor is trying to turn but is stalled), weak airflow, or a unit that endlessly cycles in an attempt to reach the desired temperature. At just $25, this part costs about what you’d spend on decent coffee for a week, and and in the Impression owners’ groups it is far and away the most common answer to “my AC won’t start”.

Parts and Tools

• Replacement dual run capacitor matched to the microfarad and voltage rating on the old one (typically 35+5 µF at 370V for Forest River Impression rooftop units) — check current price
• Needle-nose pliers or small wire strippers for disconnecting capacitor terminals
• Multimeter with capacitance setting to verify the old capacitor’s failure
• Insulated screwdriver (Phillips and flathead) for opening the AC shroud and terminal blocks
• Replacement fan motor (if motor bearings are seized or windings are burned) matched to your specific Dometic or Coleman-Mach unit
• Electrical tape or heat shrink tubing to insulate reconnected terminals

Step-by-Step Instructions

Step 1: Kill power to the rooftop AC unit

Turn off the AC breaker at your main panel and verify it’s off by attempting to power on the unit—nothing should happen. Rooftop AC runs on 120V AC and a charged capacitor can deliver a painful shock even after power is cut. Wait five minutes before touching any internal components to allow residual charge to bleed off. Take a photo of the wire positions on the capacitor terminals before you touch anything; this prevents reconnection errors that will damage the motor.

Step 2: Access the AC shroud and locate the capacitor

Climb onto the roof using a ladder and secure footing. Remove the four corner bolts holding the AC shroud (usually a Phillips head, 1/4-inch socket). Lift the shroud straight up and set it aside. The dual run capacitor is a cylindrical component mounted vertically on the frame, typically near the compressor. It has two or three wire terminals on top and a metal mounting bracket. Document its exact position with a photo before disconnecting anything.

Step 3: Test the capacitor to confirm failure

Set your multimeter to capacitance mode. Discharge the capacitor fully by touching an insulated screwdriver across both terminals for three seconds. Clip the multimeter leads to the terminals and read the value. If it reads zero, significantly below the rating printed on the side (usually 35+5 µF), or shows an open circuit, the capacitor has failed. A good capacitor will read within 10% of its rated value. This test confirms you’re replacing the right part, not chasing a motor problem.

Step 4: Disconnect the old capacitor and remove it

Using needle-nose pliers, carefully pull each wire terminal off the capacitor posts. If terminals are corroded or stuck, gently wiggle while pulling—don’t yank hard enough to break the post. Note the wire colors and positions (take a second photo if needed). Unscrew the mounting bracket bolt holding the capacitor to the frame and lift it out. Set the old capacitor aside; do not throw it in the trash—many recyclers accept capacitors due to their chemical content.

Step 5: Install the new capacitor and reconnect terminals

Position the new capacitor in the same mounting location and secure it with the bracket bolt, hand-tight first. Reconnect the wires to their original terminals using your photo as reference. The terminal positions matter: common (C) connects to the compressor, herm (H) to the compressor, and fan (F) to the fan motor. If your old capacitor had three terminals and the new one has two, or vice versa, stop and verify you have the correct replacement model before proceeding.

Step 6: Inspect the fan motor for damage or seizure

With the capacitor installed but power still off, manually spin the fan blade by hand. It should rotate freely with minimal resistance. If it’s seized, grinding, or won’t turn, the motor bearings have failed and the motor must be replaced—a capacitor alone won’t fix this. If the blade spins freely and you smell burned insulation or see discolored windings through the motor housing, the motor windings are damaged and replacement is necessary. A working motor will spin smoothly and silently.

Step 7: Restore power and test the AC unit

Climb down and turn the AC breaker back on. Set the thermostat to cool and listen for the compressor to start within 10 seconds—no hum, no delay. The fan should spin smoothly and airflow should be strong within 30 seconds. Let the unit run for five minutes and feel the condenser coils; they should be warm to hot as refrigerant cycles. If you hear a hum without the compressor starting, or the fan doesn’t spin, turn off the breaker immediately and recheck your wire connections against your photo.

Step 8: Reinstall the shroud and verify operation

Once the AC runs smoothly for five minutes with good airflow and no unusual sounds, climb back up and lower the shroud into place. Align the four corner bolt holes and hand-tighten all bolts before using a screwdriver to snug them evenly. Do not over-tighten; these are plastic shrouds and will crack. Run the AC for another 10 minutes from inside the rig to confirm stable operation, then you’re done. Most capacitor replacements solve the problem permanently; if the unit fails again within a month, the motor itself is likely failing.

What works

• Compressor fires up on the first demand instead of that hesitant pause where you can hear the motor straining before it finally engages.
• Fan delivers real cooling power—no more of that feeble trickle of air that makes you question if the unit’s even operational.
• Installation takes less than 10 minutes once you’ve safely discharged the old capacitor—just two terminal connections and one mounting bracket bolt, and you’re done.

What doesn’t

• Overnight shipping from big retailers can be a gamble when you’re boondocked 40 miles from the nearest town—plan for 3-5 days through an actual parts house, which means catching this issue early is key.
• Older Atwood or Penguin-branded AC units require different capacitor specifications—you must verify the microfarad rating (µF) and voltage of your original component before ordering, or you’ll end up with a part that fits physically but fails electrically.

When I replaced my first capacitor, I second-guessed myself because the new capacitor looked identical to the old one, but the AC was still underperforming. I later discovered that the shroud gasket was cracked and pulling warm air back in, so it’s essential not to assume that one fix will solve everything. Be sure to order the RV AC dual run capacitor (Dometic/Coleman-Mach) and test it in the shade with a temperature gun before concluding it’s not the culprit.

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