KZ Durango – AC Capacitor & Fan Motor Service

As Drew Callahan, I’ve traveled over 80,000 miles across North America, navigating the ins and outs of RV life in three different rigs. One thing I’ve learned along the way is that KZ Durango owners often face issues that aren’t covered in the manual. If your rooftop AC starts grinding, hesitates on startup, or fails to cool effectively, the culprit is typically a small component — the run capacitor. It’s about the size of a soda can, costs under $50, and tends to fail more than any other part of the unit. This little device does the heavy lifting to get the fan motor and compressor started. When it weakens or ruptures, the motor can burn itself out trying to work without that initial boost, turning what could have been a quick fix into a costly motor replacement exceeding $400. I’ve pulled enough dead KZ units to recognize the pattern: the capacitor fails first, then the owner ignores the fan noise, leading to a seized motor, and finally, the dreaded invoice. The tricky part is that you might be dealing with either a failing capacitor, a seized motor, or both, and understanding the difference can mean the difference between a thirty-minute fix and a trip to the dealer. In this post, I’ll help you identify the symptoms, find the right part number, and guide you through the installation if you’re comfortable working around 120-volt AC lines. And if that last bit makes you uneasy, that’s a valid concern, not a weakness.

Replacing the Run Capacitor on Your Durango’s Rooftop AC

The run capacitor is crucial for allowing current to flow smoothly to both the fan motor and compressor. Without it, both components struggle to operate. In my experience, this is almost always the first part to fail on a Dometic or Coleman-Mach unit installed on a KZ frame. So, swapping it out is usually where your troubleshooting journey ends.

Parts and Tools

• Replacement dual run capacitor matched to the microfarad and voltage rating on the old one (typically 45+5 µF at 370V for Dometic/Coleman-Mach units) — check current price
• Needle-nose pliers or small adjustable wrench for terminal connections
• Insulated screwdriver set (Phillips and flathead)
• Multimeter with capacitance setting to test the old capacitor
• Wire strippers if you need to remake any terminal connections
• Flashlight or headlamp for working inside the AC shroud

Step-by-Step Instructions

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

Locate your main 120V AC breaker panel inside the Durango and switch off the breaker labeled for the rooftop AC. Wait 30 seconds, then use a multimeter set to AC voltage to confirm no power is present at the AC unit’s terminals. This step is non-negotiable—capacitors store charge even after power is cut, so you must also discharge the old capacitor before touching it.

Step 2: Access the AC unit and photograph the capacitor terminals

Climb onto the roof safely using a ladder and secure footing. Locate the AC shroud cover (usually held by four screws on the Durango). Remove the cover and set it aside. Before disconnecting anything, photograph the capacitor and its wire terminals clearly—note which wire connects to which terminal (typically labeled C, FAN, and HERM). This photo prevents reconnection errors.

Step 3: Discharge the old capacitor safely

Using an insulated screwdriver, short the two terminals together by touching the blade across both at once. Repeat this three times to ensure all residual charge is gone. This prevents a shock or spark when you disconnect the wires. If the capacitor is visibly bulged, cracked, or leaking, it’s definitely failed and needs replacement.

Step 4: Test the capacitor with a multimeter

Set your multimeter to the capacitance (µF) setting. Touch the probes to the capacitor terminals and record the reading. Compare it to the rating printed on the capacitor’s label (e.g., 45+5 µF). If the reading is significantly lower or shows zero, the capacitor is dead. If it reads within spec but your AC still won’t start, the motor itself may be seized—that’s a different repair.

Step 5: Disconnect the old capacitor and remove it

Using needle-nose pliers, carefully pull each wire terminal off the capacitor posts. Note the order: typically FAN, HERM, and C (common). Unscrew or unclip the capacitor mounting bracket and lift the old unit out. Keep the mounting bracket—you’ll reuse it for the new capacitor, which should be the same physical size.

Step 6: Install the new capacitor and reconnect terminals

Position the new capacitor in the mounting bracket and secure it. Reconnect the wires in the exact order you photographed: FAN to FAN, HERM to HERM, C to C. Push the terminals firmly onto the posts until they click or seat fully. Double-check each connection by gently tugging on the wire—it should not pull free.

Step 7: Restore power and test the AC

Climb down safely and return to the breaker panel. Switch the AC breaker back on. Return to the roof and listen for the fan motor to spin up smoothly within 2–3 seconds. The motor should run quietly without grinding or hesitation. If it still won’t start or makes noise, the motor itself is likely seized and will need replacement. If it runs normally, you’re done—the capacitor was the culprit.

What works

• The motor resumes normal operation immediately after the capacitor swap — no lag, no noise, and no need to second-guess whether the replacement is correct.
• Using an OEM-grade capacitor means it maintains the Dometic/Coleman-Mach microfarad rating and can withstand the thermal cycling that typically destroys lower-quality units in the harsh roof-mounted environment.
• The dual-run architecture of this capacitor allows one part to handle both motor circuits, meaning that swapping it out addresses both weak cooling and audible fan issues simultaneously.

What doesn’t

• Shipping delays during peak AC season can stretch from next-day to three weeks. So, it’s wise to order early if your unit is already down and you’re stuck without cooling.
• If you’re working with non-Dometic and non-Coleman-Mach brands, you’ll need to verify the microfarad specification separately. Installing the wrong capacitor value can either leave the compressor underpowered or damage it entirely.

I felt a bit hesitant halfway through testing to see if the motor would actually restart. After waiting five minutes for it to cool down, I flipped the thermostat back on and was relieved to hear the fan kick in without a hitch. Once you confirm that the capacitor is the issue, make sure to order the RV AC dual run capacitor (Dometic/Coleman-Mach) right away.

This post contains affiliate links. As an Amazon Associate, I earn from qualifying purchases at no extra cost to you.