The short answer
When a Rheem AC in Northern Virginia won’t turn on, first work out which half isn’t running. If nothing runs, inside or out, it’s usually the thermostat, a breaker, or the float switch that shuts the system off when the drain backs up. If the indoor fan runs and the outdoor unit sits silent, it’s usually the outdoor unit waiting out a five-minute delay, a tripped disconnect, the contactor or the capacitor, or a fault code on the outdoor board.
Which half isn’t running?
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Swipe to see all columns →
| What you see | Usually | Start with |
|---|---|---|
| Nothing runs, thermostat blank | No power to the thermostat | The breaker, the furnace or air handler switch, the float switch, the thermostat batteries |
| Nothing runs, thermostat on | The thermostat isn’t calling | Mode set to cool and the setting under the room temperature |
| Indoor fan runs, outdoor unit silent | The outdoor unit isn’t starting | The five-minute wait, the outdoor breaker and disconnect, then the contactor or a lockout |
| Outdoor unit hums, fan doesn’t spin | A weak capacitor or the fan motor | Turn it off so the compressor doesn’t overheat, then call |
| Both run, the air isn’t cold | Refrigerant or airflow | The filter, ice on the indoor coil |
The $67 Heating Check
We check your furnace, heat pump or boiler before winter. Through December 31. See the offer
The five-minute wait is normal
After the outdoor unit stops, Rheem’s boards hold the compressor off for about five minutes so it doesn’t restart against pressure. On Rheem’s single-speed heat pumps, the two lights on the board flash back and forth during that wait. If you just changed the thermostat or the power blinked, give it five minutes before you call.
The float switch
In summer the indoor coil pulls gallons of water out of the air every day. If the drain line clogs, a float switch in the pan or the drain line cuts the system off so the water doesn’t come through a ceiling. Water in the pan under the coil, or around the furnace or air handler, means that’s why. Our condensate drain guide walks through clearing it.
Codes on the outdoor unit
Rheem’s variable-speed outdoor units show a two-digit code on the board, and on an EcoNet system the thermostat shows it too, ending in _O. For an AC that won’t start, the ones that matter are 27 (low line voltage), 48 (no voltage at the compressor, usually the contactor), 4 or L4 (the compressor couldn’t start) and 21 or 29 (a pressure switch tripped). The full chart is in our Rheem heat pump and outdoor unit codes.
The contactor and the capacitor
Most outdoor units that won’t start come down to two parts. The contactor is the switch the thermostat closes to send 240 volts to the compressor and fan; when its contacts pit or its coil fails, nothing happens outside. The capacitor gives the compressor and fan motor the kick to start; when it weakens, the unit hums and won’t spin, or starts slowly. Both are among the most common no-cool calls we run in July, and both are quick repairs once they’re tested.
What you can safely check
- Set the thermostat to cool, a few degrees under the room temperature. Replace its batteries if it has them.
- Check the breakers for the indoor and outdoor units, and the disconnect switch on the wall by the outdoor unit.
- Change the filter if it’s gray. Our filter guide covers sizes.
- Look for water in the pan under the indoor coil or a tripped float switch.
- Wait five minutes after any change.
- Reset once: turn off both breakers, the one for the outdoor unit and the one for the indoor unit, wait about a minute so the boards fully power down, then turn them back on.
What not to do
Don’t push the contactor in with a stick or a screwdriver to force the unit on. It’s 240 volts, and if the capacitor is the problem, forcing it overheats the compressor. Don’t keep resetting a breaker that trips again. If the indoor coil or the big copper line is covered in ice, set the system to off and the fan to on and let it thaw before anyone runs it again.
What a technician does
We check the line voltage (Rheem’s variable-speed units need 187 to 253 volts), test the capacitor in microfarads against its label, check the contactor and its coil, and read the board’s fault history. Once it runs, we put gauges on to see whether it’s short of refrigerant. You get the price before we fix anything.
Have a heat pump? Our heating check is $67 per system, through December 31: furnace, heat pump or boiler.
Related: Rheem EcoNet thermostat codes, thermostat not working, the thermostat C wire, AC repair, every brand in our error codes guide and our Rheem page.
Every code meaning here comes from Rheem’s own documents: P14 and P15 manual, A17 troubleshooting and P20 manual.
Call or book
A repair visit starts with a flat $99 diagnostic, or $250 after hours, and you get the price of the fix before we touch anything. Call (703) 997-9757, day or night, and tell us the code you counted, or book online from goswiftpro.com/cookiesoffer by November 30 and a box of warm MOLTN cookies comes with the heating check. Every current deal is on our offers page. Rated 5.0 stars across 1,138 reviews on Google, Angi, Yelp, the BBB and Facebook, Virginia Class A license 2705192276.
Questions people ask
Why won’t my Rheem AC turn on?
If nothing runs, check the thermostat mode and batteries, the breakers and the float switch on the drain. If the indoor fan runs but the outdoor unit doesn’t, wait five minutes and check the outdoor disconnect; after that it’s usually the contactor or the capacitor.
Why is my Rheem outdoor unit not running but the inside fan is?
The thermostat is calling but the outdoor unit isn’t starting. The usual causes are a tripped outdoor breaker or disconnect, a failed contactor, a weak capacitor, or a pressure or voltage lockout on the board.
Not one you should press. The reset is the power: turn off the breakers for the indoor and outdoor units for a minute, then back on. A lockout that comes back needs a technician.
Why does my Rheem AC wait before it starts?
The board holds the compressor off for about five minutes after it stops, so it doesn’t restart against pressure. That’s normal after a power blip or a thermostat change.
