How to Fix Cracked Dometic RV AC Covers & Roof Vents: Complete Repair

Quick Take

For your 2022 East to West 1900MMK, both issues can absolutely be fixed without full replacements. The cracked Dometic air conditioner cover can be repaired using plastic welding techniques or high-quality epoxy specifically designed for outdoor plastics, which will save you the $180-250 cost of a new shroud. Your broken roof vent cap is likely made of UV-resistant ABS plastic rather than PVC, which explains why it's held up for four years but finally succumbed to sun damage. A replacement cap runs $15-25, but you can also repair small cracks with plastic repair compounds. The key difference between vent caps is the thread pitch and diameter - your East to West likely uses standard threading, but you'll need to verify the correct part for your model (verify with dealer) before ordering a replacement.

The materials used in both components represent compromises between weight, cost, and durability. While galvanized steel would last longer, it adds significant weight to your trailer's roof load and creates expansion issues with temperature changes. Modern UV-resistant plastics, when properly maintained with protectants, can provide 8-12 years of service life in most climates.

Common Causes

Your Dometic air conditioner cover cracking at four years is actually fairly typical for travel trailers that see regular road travel and varied weather conditions. Common causes include thermal cycling - the constant expansion and contraction as the plastic heats up in direct sunlight (often reaching temperatures exceeding 150°F on the roof surface) then cools rapidly during evening hours or sudden weather changes. This creates stress points, particularly around mounting screws and any areas where the plastic has slight manufacturing variations in thickness.

Road vibration compounds this problem significantly. Every bump, turn, and highway expansion joint sends vibrations through your trailer's frame up to the roof, causing the AC shroud to flex repeatedly. The mounting points become stress concentrators, and cracks typically start at screw holes or corners where the plastic changes direction. Your East to West uses a relatively lightweight frame construction, which can amplify these vibrations compared to heavier conventional construction trailers.

For the roof vent cap, UV degradation is typically the primary enemy. Even UV-resistant plastics generally break down over time when exposed to intense sunlight, particularly at high altitudes or in desert climates, though this can vary by specific plastic type and formulation. The plastic becomes brittle and loses its flexibility, making it susceptible to cracking from thermal expansion, hail impact, or even strong winds that can cause the cap to flutter. Additionally, many manufacturers use recycled plastic content in these components to keep costs down, which can reduce long-term durability.

Chemical exposure also plays a role in both failures. Road salt, tree sap, bird droppings, and even some RV roof cleaners can attack plastic components over time. The combination of UV exposure and chemical stress creates a perfect storm for premature failure, especially in the thin-walled areas of these components where manufacturing economics drive minimal material usage.

Preparation

WARNING: Use proper fall protection and ladder safety when working on RV roofs. Never work alone or in wet/windy conditions.

Before attempting any repairs, you'll need to thoroughly clean both damaged components and assess the extent of the damage. For the AC cover, remove it completely by unscrewing the mounting screws (typically 8-12 screws around the perimeter). Clean the cover with degreasing dish soap and water, then wipe down with isopropyl alcohol to remove any residual oils or contaminants that could interfere with adhesion. Examine the cracks closely with a flashlight - are they surface cracks, or do they go completely through the plastic? Surface cracks under 6 inches can often be repaired successfully, while through-cracks longer than 8 inches may require more extensive repair or replacement.

For the vent cap, determine whether it's cracked, completely broken, or just the spring mechanism has failed. Remove the cap by unscrewing it counterclockwise (standard right-hand threads are used on virtually all RV vent caps). Measure the thread diameter with calipers and count the threads per inch using a thread pitch gauge to ensure you order the correct part for your model (verify with dealer) if repair isn't feasible.

Gather your repair materials based on your assessment. For plastic repair, you'll need either a plastic welding kit ($25-40) with ABS welding rods (most RV components are ABS plastic), or a high-quality structural adhesive like 3M DP8010 or J-B Weld PlasticWeld ($8-15). You'll also need sandpaper (120 and 220 grit), clean rags, masking tape, and potentially a small piece of fiberglass mesh for reinforcement on larger cracks. If the damage is too extensive, budget $180-250 for a new Dometic shroud or $15-25 for a new vent cap.

Safety preparation is crucial for roof work on your travel trailer. Set up on level ground and use proper ladder safety - ideally a stabilizing ladder with standoff arms to avoid putting pressure on your trailer's sidewalls. Have someone spot you, and never work on the roof in wet or windy conditions. The roof of your 1900MMK is designed for walking, but distribute your weight carefully and avoid stepping directly on the AC unit or vent assemblies.

Repair Steps

WARNING: When using plastic welding equipment, wear safety glasses and work in a well-ventilated area away from propane tanks and RV systems. Ensure propane is shut off and have a fire extinguisher nearby. Hot plastic can cause severe burns.

For repairing the cracked Dometic air conditioner cover, start by thoroughly preparing the crack area. Sand both sides of the crack with 120-grit sandpaper, creating a slight groove along the crack line and roughening the surface about 1 inch on each side of the crack. This provides better adhesion for your repair material. Clean the sanded area again with alcohol and allow it to dry completely.

If using plastic welding, set your plastic welder to the appropriate temperature for ABS plastic (typically 450-500°F). Practice on a scrap piece first to get the feel for the tool. Start at one end of the crack and slowly move the welder along the crack line, feeding the welding rod into the crack. The rod should melt and flow into the crack, creating a continuous bead. Allow each section to cool before moving to the next. Once the entire crack is welded, sand the repair smooth with 220-grit sandpaper and apply a plastic primer followed by matching paint or UV protectant.

For adhesive repair, apply the structural adhesive according to manufacturer directions. Most two-part adhesives require mixing in specific ratios - follow this precisely for maximum strength. Apply the mixed adhesive to both sides of the crack, then clamp or tape the pieces together. For added strength on larger cracks, embed a piece of fiberglass mesh in the adhesive on the interior side of the cover. Allow the full cure time (typically 24 hours) before handling or reinstalling the cover.

When reinstalling the repaired AC cover, inspect all mounting screws and replace any that show corrosion or damage. Use a thread-locking compound like blue Loctite on the screws to prevent loosening from vibration. Tighten screws in a cross-pattern to manufacturer specifications, and don't overtighten - plastic can crack under excessive clamping force. Apply a bead of self-leveling sealant around the base of the shroud to prevent water infiltration.

For the roof vent cap repair, small cracks can be repaired using the same plastic welding or adhesive techniques described above, or the cap can be replaced entirely if damage is extensive.ed using the same plastic welding or adhesive techniques described above. However, if the spring mechanism is damaged or the cap is extensively cracked, replacement is the better option. When installing a new cap, ensure the threads are clean and apply a small amount of thread sealant to prevent leaks.he threads match your existing vent body - forcing mismatched threads will damage the vent assembly. Apply a small amount of plumber's silicone grease to the threads for easier installation and removal in the future. The cap should tighten snugly but not require excessive force.

After completing either repair, apply a high-quality UV protectant specifically designed for RV applications. Products like 303 Aerospace Protectant or Meguiar's RV protectant create a barrier against UV damage and should be reapplied every 3-4 months. This maintenance step can significantly extend the life of both repaired and new components.

When to Get Help

Seek professional assistance if the AC cover has cracks longer than 12 inches, multiple intersecting cracks, or damage around the mounting points that affects structural integrity. A compromised AC cover can lead to water infiltration that damages your trailer's interior and electrical systems, making professional replacement the safer choice. Additionally, if you're uncomfortable working on the roof or lack the proper safety equipment, the risk of injury outweighs the cost savings of DIY repair.

For complex vent system issues beyond just the cap - such as damaged vent bodies, problems with the tank monitoring system connections, or suspected roof membrane damage around the vent - professional RV service is recommended. These systems integrate with your trailer's plumbing and electrical systems, and improper repairs can create expensive secondary problems. A qualified RV technician can also assess whether your roof structure has been compromised by water infiltration from the damaged components.

Consider professional help if you've attempted the repair but it's failing again within a few months. This often indicates underlying issues such as excessive frame flex, improper mounting, or more extensive damage than initially apparent. A professional can assess the root cause and implement a more permanent solution, potentially including structural reinforcement or upgraded mounting systems that better handle road stress.

Finally, if your trailer is still under warranty, check with East to West before attempting any repairs. While four-year-old components are likely beyond the standard warranty period, some manufacturers offer extended coverage on roof components due to their critical nature. Attempting DIY repairs on warranty-covered components can void coverage, so verify your warranty status first. Even if not covered, your dealer may offer discounted parts or labor for known issues with your specific model year.