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I have two AC units--one for upstairs and one for

Customer Question
Hi, I have two...

Hi, I have two AC units--one for upstairs and one for downstairs. The fan for the one for upstairs has been starting and stopping every few seconds, even though the temperature is set to below what it is. This isn't happening for the downstairs unit. Any thoughts on why the fan for the AC unit upstairs is doing this? Thank you!

Contractor's Assistant: Did you double-check the thermostat? And what about the unit's filters?

I did check the thermostat--it's set at 72 and the temperature is at 76, so it should be running. I just changed the filters so they aren't clogged or anything

Contractor's Assistant: Do you plan on doing the work yourself?

Not necessarily, but if it's something simple, I am ok with fixing it myself

Contractor's Assistant: Anything else we should know to help you best?

No, it's just the fan starting and stopping problem

Submitted: 8 months ago.Category: HVAC
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Answered in 12 minutes by:
9/30/2017
HVAC Technician: Regan Land, HVAC Technician replied 8 months ago
Regan Land
Regan Land, HVAC Technician
Category: HVAC
Satisfied Customers: 768
Experience: Over 20 years of experience, NATE Certified, Licensed HVAC Contractor, Certified IAQ Specialist
Verified

Hello and welcome to Just Answer. My name is ***** ***** I'll be happy to assist you today. Is it the indoor blower or the fan on the outdoor unit that is giving you the problem?

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Customer reply replied 8 months ago
Fan on the outdoor unit
HVAC Technician: Regan Land, HVAC Technician replied 8 months ago

Okay, thank you. Do you hear the compressor running when the fan turns off? Or is it silent when the fan turns off?

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Customer reply replied 8 months ago
I believe the compressor is quiet when the fan isn't running...
HVAC Technician: Regan Land, HVAC Technician replied 8 months ago

Strange - do you feel comfortable removing the panel on the outdoor unit? If so, go ahead and do so and watch what's happening when the fan turns on/off. There's a contactor in there (that the main power coming into the unit connects to) that I'd like to see if it's pulling in and popping out or if it stays pulled in the entire time.

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Customer reply replied 8 months ago
I'm nor comfortable doing that partly coz it's slushy there...I thin I'll just call a tech guy
HVAC Technician: Regan Land, HVAC Technician replied 8 months ago

I completely understand - but if you feel comfortable let's try one thing inside before you call a tech out. Can you remove the face of the thermostat to expose the wiring? It's low voltage there so won't hurt you. If you're comfortable, remove the yellow wire from the Y terminal and put it in the R terminal with the red wire. Then check the outdoor unit and see if it's still short cycling.

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Customer reply replied 8 months ago
We have a nest thermostat, so not sure if this can be done?
HVAC Technician: Regan Land, HVAC Technician replied 8 months ago

It can. Connecting the wires together will bypass the themostat, so you won't put the face on while they're bypassed. You can just slip the yellow wire into the terminal with the red wire.

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Customer reply replied 8 months ago
Not sure how to open the nest thermostat. Do I just pull the cap off?
HVAC Technician: Regan Land, HVAC Technician replied 8 months ago

Yes, just pull the face of the thermostat directly away from the wall

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Customer reply replied 8 months ago
Ok done. When you say remove yellow wire and put it in with the red wire, do I force it in there? There's not much space for an extra wire
HVAC Technician: Regan Land, HVAC Technician replied 8 months ago

You should be able to get two wires in there - If not, you can remove the red wire and twist them together or someone can hold the wires together while someone else watches the outdoor unit.

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Customer reply replied 8 months ago
Ok. So what would be a good sign after they are wired together?
HVAC Technician: Regan Land, HVAC Technician replied 8 months ago

We're hoping the outdoor unit will stay running

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Customer reply replied 8 months ago
Nope, it switches on and off--like before. Also, I noticed that for the unit that's working the pipe out of the compressor is cool/cold, but not so for the unit that switches on and off--maybe because it only runs in short spurts
HVAC Technician: Regan Land, HVAC Technician replied 8 months ago

Okay, looks like the problem will be with the outdoor unit. The unit has to run for a bit before the suction line gets cold. There's a good chance that the unit is low on refrigerant and when the compressor comes on it pulls refrigerant down low enough to trip the low pressure switch - then when the comressor turns off the pressures equalize and resets switch which allows the unit to come back on. I would definitely recommend you turn the thermostat off until a technician can check the system. If the compressor is turning on and off like that it could damage it causing a very expensive repair.

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Customer reply replied 8 months ago
Ok thank you!
HVAC Technician: Regan Land, HVAC Technician replied 8 months ago
You're welcome!
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