AC unit won't turn on: both inside blower fan and outside fan unit won't turn on. It is as if I had gone to the circuit breaker and cut the power to the whole HVAC system, but I didn't. I've been searching around and saw that in most cases, either the inside or the outside unit won't turn on, but I have not found a case where both won't turn on.

The outside unit has a disconnect box that contains no fuse. I've double checked that the rabbits didn't somehow manage to take the connector piece out...

I've also replaced the old mercury-based thermostat with a new digital, battery-powered thermostat, which didn't help. I can hear the clicking sound it makes to turn on the AC, but nothing else happens.

It was working fine 5 days ago. I turned it off for 5 days straight, and now it won't turn on again.

I'm trying to get an HVAC pro to come and take a look, but they're booked until next week. Is there anything else I can check in the mean time?

EDIT: I'd like to open up the access control panel to check for fuse locations, but I cannot figure out how to do so. Here's a picture of what I assume to be the panel door. I've tried prying it open from all 4 sides with a flathead driver. It also doesn't slide in any direction. Any suggestion?

access control panel door

Additionally, I've verified that there is electricity in the unit. There is voltage in that the exterior white wire going from the box to the thermostat (see picture) and there's also voltage going through the disconnect box and into the outside fan unit...


I was able to take the control panel door off, and found that it's getting no electricity. As you can see in pic1, the exterior white wire is live and it goes in the little box with the black push switch to the left of the picture. However, in pic2 the three internal wires (green, white, and black) going out of the box are not live.

Pic1 - electricity going into the little box

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Pic2 - no electricity going out of the little box

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Additionally, the red status light that used to be on all the time (which I didn't recall till now) is now off.

Pic3: red status light no longer on.

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So what is this little box and could it be the cause?

enter image description here

  • Do you have a volt meter or multimeter? Are you comfortable poking around in the HVAC equipment?
    – Tester101
    Jun 12, 2015 at 18:59
  • Do you have a furnace, or air handler? If you have a furnace, does the heat work?
    – Tester101
    Jun 12, 2015 at 19:00
  • I don't have a meter... but I will pick one up this evening. I have a furnace, although it's currently too hot (~90 F) for the heater to come on.
    – Zoomzoom
    Jun 12, 2015 at 19:12
  • Did you check the breakers to make sure they're not tripped? Sometimes when they trip, they don't move all the way to the OFF position, so they can appear to be ON.
    – Tester101
    Jun 12, 2015 at 22:42
  • Thanks, I've flipped the breaker switch off and on several times to no effect. I've called the tech and they'll come next week to diagnose the problem. I'll report back what the problem is.
    – Zoomzoom
    Jun 13, 2015 at 18:02

1 Answer 1


As it turns out, the box in the last picture is a safety measure which cuts the electricity when the panel door is removed. Turns out, there were a couple of screws on the outside that secure this box that were missing. Why? I did it (DOH!). I removed them a few days back when trying to open this panel door so that I can do the "G wire to C wire" switch for a new thermostat. Well, put those back and it's working now.

  • 1
    Glad you figured it out, you probably saved yourself a couple hundred bucks, and an embarrassing service visit.
    – Tester101
    Jun 16, 2015 at 1:59

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