RV AC not cooling: the check, the cause, and the cost

A rooftop AC that will not cool on a 95-degree Montgomery County afternoon is one of the most common calls we get, and most of the time it is a $200 to $350 capacitor, not a $1,200 to $2,500 replacement.

Check this first (five minutes)

Does the fan run? No air movement at all: check the breaker or the pedestal power before assuming the unit is broken.
Fan runs, a hum, then nothing starts. Classic capacitor symptom. The compressor is trying and failing to start.
Look through the return grille for ice on the coil. Ice means restricted airflow, usually a dirty filter or a dirty coil, not necessarily a broken compressor. Turn the unit off and let it thaw before running it again.
Feel the vent air temperature versus room temperature. A rooftop unit only pulls the air about 15 to 20 degrees below ambient by design, so on a 100-degree day, 80-degree vent air can be normal, not broken.
Note any smell. Musty on startup that fades: mold on the coil. A hot electrical smell: stop running it and call.

What is usually wrong

What you find	Likely cause	Fix and cost
Fan runs, compressor hums and stops	Failed start or run capacitor	$200 to $350
Ice visible on the coil	Restricted airflow, dirty filter or coil	Clean and clear: $200 to $400
Musty smell on startup	Mold on the evaporator coil	Coil and pan cleaning: $200 to $450
Water dripping inside on a humid day	Clogged condensate drain	AC service: $200 to $450
Runs constantly, never quite cools	Undersized unit for rig, or low refrigerant	Diagnose on site before quoting
No sound, no fan, no power at all	Breaker, power source, or control board	$150 to $600 depending on cause
Compressor fails to start, capacitor tests fine	Likely compressor failure	Replacement: $1,200 to $2,500

Ranges from the pricing page, on top of the $75 to $150 trip fee and $125 to $190 hourly labor.

Why this happens in Montgomery County

Rooftop units here run under two stresses most of the year: Texas heat, which shortens capacitor life and pushes the unit near its cooling limit on the hottest afternoons, and Gulf Coast humidity, which grows mold on a coil that stays wet between cycles for most of the muggy season, roughly mid-April into late October. Pedestal or storage-yard power sagging on a hot afternoon, when several rigs run AC at once, also stresses starting components. An EMS or surge protector that also catches low voltage helps here.

What to expect on the call

Tell us whether the fan runs, whether you saw ice, and whether there is a smell. That narrows the diagnosis before we arrive. We work on site across Conroe, Montgomery, Willis, The Woodlands, Magnolia, New Caney, and Huntsville. The AC repair service page covers what a full diagnosis or replacement involves, and the repair cost calculator prices your specific symptom now.

Frequently Asked Questions

My AC fan runs but the compressor does not start. What is that?

Almost always the start or run capacitor. It is the most common rooftop AC failure we see, it runs $200 to $350 to fix, and it is a same-visit repair when the part is on the truck, which it usually is.

There is ice on the coil. Should I keep running the AC?

No. Turn it to fan-only or off and let it thaw. Running a frozen coil forces the compressor to work against restricted airflow, which is how a simple airflow problem turns into a compressor failure.

Why does the air smell musty when the AC first kicks on?

Mold on the evaporator coil, from humidity condensing on a coil that never fully dries between cycles. A coil and drain-pan cleaning, usually $200 to $450, fixes it and is not a sign the unit needs replacing.

How much does it cost if it turns out to be the compressor?

A failed compressor on a rooftop unit is a replacement conversation, not a repair, since swapping a compressor on a sealed system is not economical. Full unit replacement runs $1,200 to $2,500 installed for a standard 13.5K to 15K BTU unit.