5 Tips For When the Outside AC Unit is Not Running But Inside is

juan molina
3 min readNov 25, 2020


There are several reasons why the outside ac unit may not be running, while the inside unit is. This article will go over the 5 top things you might want to try, before calling out a professional.

Tip One

Sometimes there are power surges due to lightening strikes. In this case, you might find that a breaker might have been activated. Just check in your breaker panel to see if the breaker for the outside ac unit is in the off position. In this case, all you need do is to flip the switch back to the on position. If by chance, the breaker flips off again, you have an electrical short in the system. This would be good time to call on a professional.

Tip Two

Sometimes there occurs a Brown-Out. This is when one of the two power lines to the outside ac unit looses power, for just a second. This causes the compressor, inside the unit, to stop running. As soon as the power turns back on, the compressor attempts to activate again, but pressure, that has been built up in the system, serves as a restriction to the compressor. This may keep the compressor for turning on, and with power flowing to the compressor, that causes a situation that is called “thermal overload.” In this state, the compressor over heats and a safety switch, that most units have built in, will prevent the compressor from turning back on.

In this case, go to the breaker box, and locate the breaker to the outside ac unit, and shut it off for up to two hours. In this time, the compressor will cool off, and the switch will turn back to its normal mode, allowing the unit to run again. Turn the power back on and check. If at this time the unit is not running, got to the next tip.

Tip Three

Some installers may place a safety float switch at the inside unit. That switch may be wired up to shut the outside unit down, if the drain line fills with water and is not draining. To check, Most float switches have a removable top, that lifts off, remove it and check for standing water. Usually, if that’s the problem, you will notice that the outside unit has started running gain.

To handle this problem, apply a wet/dry vacuum to the outside drain line. Wait several minutes, to see if the unit turns back on. You can also check by the inside unit to see if you can hear the vacuum at that point. You may want to consider having professional do a deep clean of the drain line, since usually, a clogged drain line is mainly caused by a type of calcification that occurs in standing water.

Note: If the inside unit is in the attic, I do not recommend that you try going into the attic. Only apply the vacuum, and check if this works for you.

Tip Four

Sometimes, landscapers get too close to the outside unit, and snip the control wires. These are low voltage wires that control the outside unit, and if snipped, do not let the unit turn on. In this case, you must shut the power down to inside unit at the breaker. This will prevent the transformer, that’s inside the inside unit, from shorting out. At this time you may reconnect the wires. Just note to not allow the two wires, of the control wires, to touch. This will cause the transformer to short. You may insulate the wires with black tape, but wire nuts are the preferred method.

Tip Five

Some older Rheem units have a reset button on the exterior of the outside unit. Simply depressing it will cause the unit to reactivate.

What To Do If All Else Fails

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