How to Add Coleman Mach Heat Strips to RV AC Unit - Heat-Ready Control Box Installation Guide

The Quick Answer

Yes, you can typically upgrade Cool-Only Control Boxes to Heat-Ready versions and add Coleman Mach Electric Heat Strips to both your 13.5k BTU and 15k BTU A/Cs while retaining full furnace functionality. You'll need to replace your cool-only control boxes with Coleman Heat-Ready Control Boxes (pricing varies), checking compatibility with your specific Mach units. For your configuration, you can keep the bedroom setup simple with one thermostat controlling A/C and heat strip, while the main cabin can use an advanced WiFi thermostat that can control A/C, heat strip, and furnace with configurable backup options.

What's Causing This

Your current Cool-Only Control Boxes are designed specifically for air conditioning only and lack the electrical connections and control circuits needed for electric heat strips. These control boxes contain the main electrical contactors, capacitors, and control logic that manage the A/C compressor and fan motors, but they're missing the heating element contactors and safety circuits required for heat strips. Verify compatibility between your specific control box and heat strip models before ordering.

The good news is that Coleman designed their system with upgrade compatibility in mind. Your Mach 3 Plus and Mach 15 Plus units (verify exact model numbers on unit labels) have the physical space and mounting points for heat strips built right in. The electrical infrastructure in your RV should also support this upgrade since modern RVs typically have 30 or 50-amp service with adequate wiring capacity. Perform electrical load calculations to verify your panel capacity before installation. Heat strips typically draw 15-20 amps each, so two strips plus existing loads may exceed 30-amp RV service capacity. Calculate total amperage: existing loads + heat strip amperage (see manufacturer specifications) to ensure it doesn't exceed your RV's electrical panel rating.

The complexity comes with integrating multiple heat sources (heat strips and furnace) through a single thermostat in your main cabin area. Most standard RV thermostats can only control one heating source at a time, which is why you'll need a more sophisticated control system for your main cabin setup while keeping the bedroom simpler.

Tools You'll Need

• Digital multimeter for testing electrical connections
• Wire strippers and electrical tape
• Phillips and flathead screwdrivers
• 10mm and 7/16" wrenches for A/C unit removal
• Cordless drill with bits for thermostat mounting
• Wire nuts and electrical connectors
• Label maker or masking tape for wire identification
• Flashlight or headlamp for working in tight spaces

Step-by-Step Fix

Phase 1: Control Box Upgrades

1. Order compatible Coleman Heat-Ready Control Boxes and heat strips (verify current part numbers and pricing with Coleman)
2. Turn off power at the main panel and verify it's off with your multimeter. WARNING: Working on A/C refrigerant systems may require EPA certification and proper refrigerant handling procedures
3. Remove the A/C shrouds and follow manufacturer procedures to safely access the control boxes by removing electrical connections only
4. Take photos of all existing wiring before disconnecting anything
5. Remove the old 8330-752 boxes and install the new 8530-752 units using the same mounting points
6. Reconnect all original A/C wiring to the corresponding terminals on the new boxes

Phase 2: Heat Strip Installation

1. Install the 37203-4551 heat strips in both A/C units following Coleman's instructions
2. Connect the heat strip power leads to the heating terminals on your new 8530-752 control boxes
3. Verify all connections are tight and properly insulated
4. Test each system individually before proceeding

Phase 3: Thermostat Setup

1. For the bedroom: Verify your existing thermostat supports heat strip control, or replace with a compatible model. Run appropriate thermostat cable as specified by the control box manufacturer
2. For the main cabin: Install a Coleman 9630-3362 WiFi thermostat ($200) which can control A/C, heat strip, and furnace with priority settings
3. Configure the main cabin thermostat to use heat strip as primary and furnace as backup, or vice versa, depending on your preference
4. Set up the WiFi connectivity through the Coleman app for remote control

Phase 4: Testing and Configuration

1. Test each zone independently in both cooling and heating modes
2. Verify the main cabin can switch between heat sources as programmed
3. Check that the furnace still operates independently when needed
4. Set up backup heating logic in the advanced thermostat settings

When to Call a Pro

Call a certified RV technician if you discover that your RV's electrical system doesn't have adequate amperage capacity for the heat strips (amperage requirements vary by heat strip wattage - see manufacturer specifications), or if you're not comfortable working with 120V electrical systems. The heat strip installation involves working with high-amperage heating elements, and improper installation can create fire hazards.

Also consider professional help if you want to integrate additional smart home features or if your WiFi thermostat installation requires running new thermostat cables through finished walls and floors. Some RV service centers specialize in HVAC upgrades and can complete this entire project in a day while ensuring all work meets RV electrical codes.

Professional installation typically costs $800-1200 in labor, but ensures proper load calculations, code compliance, and warranty protection on both the equipment and installation work.