RV Air Conditioning That Will Not Keep Up

A rooftop RV air conditioner working in a Florida panhandle August is doing about the hardest job it will ever do. When it stops keeping up, the cause is usually airflow or power rather than a dead compressor.

Work through it in order before assuming the worst.

Filters first

The return air filter is the single most common cause of a unit that runs constantly and does not cool. It is easy to reach, it is cheap, and it gets ignored for years.

A clogged filter restricts airflow across the evaporator, which drops capacity and can freeze the coil. A frozen coil produces exactly the symptom people describe as the unit not cooling.

Coils

The condenser coil on the roof packs with dust, pollen and debris, and a coil that cannot reject heat cannot cool the inside. Cleaning it is straightforward and it makes a real difference.

The evaporator coil inside can also foul, particularly if the filter has been neglected.

Power is the other half

Air conditioners need voltage to run properly. On a marginal campground pedestal, long extension cords, or a generator that is not keeping up, low voltage makes the compressor work hard, run hot and eventually shut down on thermal overload.

Symptoms of low voltage are a unit that starts and then stops, dimming lights when the compressor kicks in, or a unit that will not start the compressor at all while the fan runs fine.

Running an air conditioner on low voltage is how compressors die. If the pedestal is marginal or you are on a long cord, a voltage monitor is worth having and worth paying attention to.

Capacitors

Start and run capacitors are a common failure on rooftop units and they produce a specific symptom: the fan runs, the compressor hums but does not start, and the unit blows warm air.

It is a relatively small part and it is one of the most frequent repairs on these units.

Frozen evaporator

If the unit cools for a while and then output drops off, then recovers after being off for a period, the coil is icing. Causes are restricted airflow from a dirty filter or coil, low refrigerant, or running the unit when the outside temperature is too low for it.

Ice on the coil means the unit is not moving enough air across it.

Ducted versus non-ducted

On ducted systems, blocked or collapsed ducting reduces output at some vents while others work fine. That is a duct problem rather than a unit problem, and it gets misdiagnosed regularly.

Check whether all vents are open and whether output is even across them.

Realistic expectations

A rooftop unit is sized to hold a temperature difference from outside, not to make a hot rig cold quickly. A coach that has been sitting closed in a Florida parking lot all afternoon takes a long time to pull down, and a single unit on a large rig may never fully catch up on the hottest days.

Shade, reflective window covers, running the unit before the rig gets hot, and keeping vents closed all matter more than people expect.

Refrigerant

These are sealed systems. If refrigerant is low, there is a leak, and most rooftop units are not serviceable in the field for refrigerant. A unit that is genuinely low is usually a replacement rather than a recharge.

That is why the airflow and power checks come first — they are the fixable causes.

Two units and one generator

Rigs with two rooftop units frequently cannot run both on a single generator or on a 30 amp pedestal. Trying produces breakers tripping or both units running badly on inadequate power.

Knowing what your service actually supports, and managing which loads run together, prevents damage as well as frustration.

Soft start devices

Compressor startup draws far more current than running does, which is what trips breakers and what a marginal generator cannot supply. Soft start devices reduce that inrush and are a common addition on rigs that camp on limited power.

Worth knowing about if you are regularly on a 30 amp pedestal with two units.

Before you call it dead

The order that finds most of these is filter, coils, voltage, capacitor. Three of those four are things an owner can check or clean, and they account for the large majority of units that will not keep up.

A compressor that has genuinely failed is the least common answer, not the first one.

If your unit is not keeping up and you have checked the filter and the coils, call (850) 495-0366. Dispatch is answered 24 hours and James comes to the rig wherever it is parked.