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- Run time
How long does it run in an hour?
Time it on a hot afternoon and put the figure in. The gauge says what that run time is telling you about sizing, airflow and whether the house is being dried out at all.
The gauge
Pick a genuinely hot afternoon — the hottest part of the day, doors shut, nothing unusual going on. Watch the outdoor unit for an hour and add up the minutes it actually runs. That single number tells you more about a system than any other thing you can measure without tools.
What that run time means
Running only a few minutes at a time means the coil barely gets cold before the thermostat is satisfied. The temperature comes down; the moisture does not. On this coast that is the difference between a house that feels cool and a house that feels cold and damp at the same time.
- Check the filter and the return first. Restricted airflow shortens cycles and is the cheapest thing to rule out.
- Check the thermostat is not in a draught, in sunlight, or above a supply register.
- If those are fine, the system is very likely larger than the house needs. That cannot be repaired — it is fixed at replacement, with a load calculation.
- A variable-speed or two-stage system is the usual answer where oversizing is confirmed, because it can run long and slow.
Cycles of this length give the coil time to get properly cold and pull moisture out of the air before the thermostat is satisfied. This is roughly what you want to see in ordinary summer weather here.
- If the house still feels damp at this run time, look at the airflow setting — pushing too much air makes a system better at cooling and worse at drying.
- Check the condensate is actually leaving the building. Water that cannot drain ends up back in the air.
- Nothing here suggests a sizing problem.
A system sized properly for this climate is supposed to run most of the hour when it is genuinely hot outside. Long cycles are how a house gets dried out, and a system that never runs long is the one with a problem.
- Since the house is holding temperature, this is the system doing its job rather than struggling.
- Long run times do cost more to run on a hot day. That is the weather, not a fault.
- Worth checking the coil and filter anyway — a dirty system reaches this run time on a day that should not need it.
The house drifting up while the system runs is the combination worth acting on: whatever the run time says, the system is not meeting the load. In the great majority of cases that is not because the equipment is too small — and the longer the run time, the more certain that is.
- Coil condition, indoors and out. A condenser packed with dust or a dirty evaporator will do exactly this.
- Refrigerant charge. Low charge from a leak produces this pattern and gets worse.
- Duct leakage in a hot attic, which throws away a large share of what the system makes before it reaches a room.
- Only after all three would anybody sensible talk about capacity — and then from a load calculation, not from a guess.
Run time depends on how hot it is outside, what the house is doing and where the thermostat sits, so one reading on one afternoon is an indication rather than a diagnosis. Time it over two or three hot days before drawing conclusions, and never use it on a mild day — short cycles in mild weather are normal for any system.
What the gauge cannot do
- It does not measure humidityIt infers a problem from cycle length. A cheap hygrometer in the room is a better direct measure and worth owning on this coast.
- It does not size anythingWhere a system turns out to be oversized, the replacement is sized from a load calculation — not by going one size down from what is there.
- It is not a reason to raise the setpoint and hopeIf the house is losing temperature with the system running flat out, something is wrong and it will not fix itself.