Changeover is the moment a rooftop unit stops making cold air and starts making warm air, and it happens because one part slides. The reversing valve is a brass body with a spool inside it that swaps the job of the two coils. In cooling, the ceiling coil is the evaporator and the rooftop coil is the condenser that dumps heat outside. In heating, the Coleman-Mach service manual describes those same coils relabeled: the outdoor coil becomes the evaporator and the indoor coil becomes the condenser. Nothing else in the box reverses. The compressor turns the same direction, the fan blows the same way, and the 20 ounce refrigerant charge never moves. A small 12 volt solenoid coil shifts the spool, and it takes its signal from the thermostat, either the O or B terminal on most controls or a reversing valve relay in the ceiling assembly on ducted Coleman-Mach plenums.
A heat pump does not create heat. It moves heat that already exists in the outside air into the coach, so as the outside air gets colder there is less of it to move and the outdoor coil starts collecting frost instead. Every manufacturer solves this the same way, by refusing to run. Dometic states it plainly: the Single Zone LCD thermostat carries a low ambient lock out that prevents heat pump operation below 30 degrees Fahrenheit, and the CCC 2 control hands the coach over to auxiliary heat below 30 degrees and will not give the heat pump back until the outdoor sensor reads above 35. Airxcel is blunter still, telling owners a heat pump will not operate at ambient temperatures below freezing and should never be treated as a total replacement for a furnace. The Coleman-Mach service manual puts its own shutdown at approximately 40 degrees.
The second most common false alarm is a heat pump that heats, then blows cold for a few minutes, then heats again. That is the defrost cycle, and Dometic publishes the exact sequence. When the outdoor sensor reads below 42 degrees Fahrenheit and above 30, the CCC 2 limits continuous compressor run time to 25 minutes. The unit then reverses flow into cooling for up to 4.5 minutes to melt frost off the outdoor coil. The display toggles between HP and Defrost while this happens. Flow then reverses back, and after a 30 second delay the fan resumes. Dometic's own wording in the Single Zone manual is that the user will temporarily feel cold air at the registers, that this is normal, and that it is not an indication of malfunction.
The order matters, because five of the six checks happen before anyone climbs on the roof. First is the outdoor temperature and, on Dometic systems, what the thermostat's own outdoor sensor is reporting, since a shorted sensor fakes a cold night in July. Second is configuration: the number 7 DIP switch that tells a Dometic power module it is driving a heat pump, or the sub-base position on a Coleman-Mach system. Third is the signal, metered right at the terminal board, looking for 12 VDC on the changeover output while the thermostat calls for heat. Fourth is the reversing valve solenoid coil itself, checked for resistance with the leads pulled, because an open coil reads infinite. Fifth is the valve body, read with an infrared thermometer for a temperature split across its lines. Only then does the compressor come into question.
What separates the cheap outcomes from the expensive one is where the fault sits relative to the sealed circuit, and the cheap ones are also the common ones. A failed changeover relay, a thermostat that never sends the changeover signal, or a corroded terminal board connection are each a part plus time, reached from the ceiling assembly or the thermostat sub-base without opening anything on the roof. A burned reversing valve solenoid coil runs longer, because the coil sits under the rooftop shroud and the unit has to be opened up there. A genuinely stuck valve spool is the branch that ends the repair: these are sealed capillary tube systems with no service ports, so the practical fix is a replacement rooftop unit rather than a valve, and that becomes a decision about the coach rather than about the part. Left alone, a coach with no changeover simply runs its LP furnace or its 5,600 BTUH heat strip all winter, which turns a one time repair into a recurring fuel bill.
Florida is the one place an RV heat pump genuinely earns its keep. Winter overnight lows across the peninsula sit mostly in the 40s and 50s, above every lockout threshold in the manuals, so a Florida coach can run heat pump heat on almost every cool night of the season. That is also the source of the confusion. On the handful of nights a front drops the temperature into the 30s, a unit that has worked for three months simply stops, and nothing has failed. The cooling season creates a second, quieter problem. A valve spool that spends nine months of sustained 90 plus degree heat parked in the cooling position is a spool that has not moved in nine months, which is exactly why a stuck valve announces itself on the first cold snap rather than at the height of summer.
The manufacturer's own spec table settles this. A 15,000 BTU Coleman-Mach heat pump draws 1,675 running watts in heating mode at 47 degrees outdoor, which at a metered rate near 15 cents per kilowatt hour works out to roughly a quarter an hour, and at most Florida parks that electricity is already inside the nightly site rate. A 30,000 BTU furnace at full fire burns about a third of a gallon of propane an hour, since propane carries roughly 91,500 BTU per gallon. At Florida bottle prices that is well over a dollar an hour. The catch is capacity rather than cost. That same heat pump makes 12,700 BTU at 47 degrees, while the electric heat strip that replaces it at lockout is rated 5,600 BTU, so the furnace remains the only thing that will hold a coach on a genuinely cold night.
We are fully mobile and come to you anywhere in Florida - campgrounds, storage lots, driveways and RV parks.
Call 888-759-1438No, and neither can anyone else. RV rooftop heat pumps are sealed systems with a capillary tube metering device and a factory charge, 20 ounces on a 15,000 BTU Coleman-Mach unit, and they leave the factory with no service ports to connect gauges to. If a rooftop unit has genuinely lost charge, the repair is a replacement unit rather than a recharge. Any shop offering to top one off is guessing at both the charge weight and the leak.
It depends on the brand, and the single number owners repeat is not universal. Dometic thermostats lock the heat pump out below 30 degrees Fahrenheit and restore it above 35. The Coleman-Mach service manual gives approximately 40 degrees, enforced by a freeze switch on the condenser coil that opens at 18 degrees plus or minus 6 of actual coil temperature rather than air temperature. Airxcel simply states a heat pump will not operate below freezing.
That is the defrost cycle, and it is normal. With the outdoor sensor between 30 and 42 degrees the control caps compressor run time at 25 minutes, then reverses flow into cooling for up to 4.5 minutes to melt frost from the outdoor coil. The display reads Defrost, then flow reverses back and the fan restarts after a 30 second delay. Dometic's own wording is that feeling cold air at the registers during it is not an indication of malfunction.
Usually not. Cooling is the reversing valve's unpowered rest position, so a unit that cools perfectly and never heats has already proven the compressor, the fan and the refrigerant charge are fine. What has failed sits in the changeover path: the thermostat signal, the reversing valve relay, the solenoid coil, or the valve spool. Three of those four are inexpensive parts, and the diagnosis is a meter reading rather than a guess.
Run the heat pump on any night forecast above the mid 40s, which in Florida is most of them. It costs a fraction of what propane costs per hour and it will hold a coach comfortably at those temperatures. Switch to the furnace when a front pushes lows into the 30s, because the heat pump will lock out anyway and the electric heat strip behind it is rated at less than half the heat pump's output.
Every figure on this page comes from a manufacturer document or a standards body, not from another repair site. Here is where each one comes from.
| Item | Price | What it covers |
|---|---|---|
| Service call | $299 | Includes the trip out to your RV and the first hour on site |
| Work past the first hour | Quoted after diagnosis | We tell you what it will take before we carry on |
| Parts | Quoted per job | Special-order parts may need a deposit before we order them |
| Written estimate | No charge | You approve the estimate before any work starts |
The service call covers the trip out to your RV and the first hour on site. Anything beyond that depends on what we find, and we quote it and get your approval before carrying on.
The price ranges on this page come from our own recent jobs across Florida, not from an industry average. What you pay depends on the rig, the parts it needs and what we find on site, so we give you a written estimate before any work begins and you approve it first.