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? 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. 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 Pic2 - no electricity going out of the little box 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.

So what is this little box and could it be the cause? 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. 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. That unit is a bowl of spaghetti for a homeowner to be expected to work on this while hot, potentially lethal situation where 1 error may be the last you make is not something I recommend you attempting. this units wiring while not bad is not user friendly and power sure isn'tBrowse other questions tagged hvac air-conditioning central-air or ask your own question.Air conditioner or heat pump won't start: What to check if your air conditioner or heat pump just won't start at all. Here we give a diagnostic sequence of things to check if the A/C is just not working.

Checking these simple items, switches and controls, including some you may not know about (overflow pan switch for example) may get your system running without a costly service call. This article forms part of our series on how to diagnose an air conditioner or heat pump that is not cooling: this article explains how to diagnose and correct air conditioning problems like lost or reduced air conditioner cooling capacity, reduced or no cool air flow, reduced or no actual lowering of the air temperature, or an air conditioner that won't start.air handling unit reviews Is there no cool air at all coming out of the supply registers? control board on ac unitIs the air conditioner or heat pump indoor or outdoor unit silent? ac unit 15 000If so it's not running.

Here is what to check first. Here are the details of what to check in what order if your air condtioner or heat pump doesn't start at all when you set the room thermostat to call for cooling: If the air conditioning system is still not working, or if the A/C system is running but cool air is not coming out of the supply check the following: Air conditioner won't turn on, or fan won't turn on or won't turn off. See THERMOSTATS for a discussion of how air conditioner thermostats work and how the air conditioner blower fan controls work. See MOTOR OVERLOAD RESET SWITCH just to be sure that the air handler blower fan motor has not shut off on thermal overload. And if your blower fan is driven by a fan belt and an electric motor, of course check to see that the drive belt is in place and un-damaged. If the blower fan belt is broken the electric motor will run just fine (you may be able to hear it) but the blower fan assembly itself won't be turning. If the air handler or indoor blower assembly does not start in response to a call for cooling the no-start problem is probably at the indoor thermostat or at the blower assembly itself.

If the indoor air handler blower runs but the outdoor compressor/condenser unit never starts then the problem is more likely there. If the indoor air handler runs but the outdoor compressor/condenser does not, see COMPRESSOR / CONDENSER DIAGNOSTICS 1. Check that electricity is on for the equipment, everywhere. Check all switches and controls, including service switches, including outside by the compressor, inside at the air handler, and fuses or circuit breakers in the electrical panel. See KEY HVAC SWITCHES service switches, circuit breakers, fuses, power 2. Check all of the safety and interlock switches: For example, condensate spilling into an overflow pan that uses a sensor switch can be enough to shut down your air conditioner. There are several switches and controls, both manual and automatic that can leave an air conditioner or heat pump turned "off" such as a blower compartment door interlock safety switch See A/C - HEAT PUMP CONTROLS & SWITCHES to be sure you have found and checked every manual or automatic electrical switch on the system both at the outdoor compressor/condenser unit and indoors at the air handler and duct system.

Electrical problems: air conditioning system won't start: it may sound silly, but is the air conditioner turned on? Has the cooling thermostat been set to "cool" and the temperature set below ambient room temperature? Do both the outdoor compressor/condenser unit and the indoor blower fan/evaporator coil unit have electrical power? Has the air conditioning electrical wiring been physically damaged or cut? Photo courtesy of Tim Hemm. Are the power switches on at these units, are the fuses good, are the circuit breakers in the "on" position, and is the thermostat set correctly? Air conditioner compressor problems, including compressor noises, hard starting, and burned-out compressors, are explained in detail beginning at COMPRESSOR & CONDENSING COIL and including topics such as 3. Check for a blown fuse locally inside the air handler, such as on or near a control board. 4. Check for a bad contactor or start relay inside the air handler or outside at the compressor/condenser unit

5. Check (or your service tech will check) for a bad or failed starter capacitor for the fan motor in the blower assembly or outdoors at the compressor/condenser unit could also be leaving your system shut down, failing to start a blower motor fan indoors or outside the compressor condenser unit's fan, or compressor motor. If an electric motor hums but won't start or won't keep running the problem could be a bad start/run capacitor. Of course a frozen bearing or burned-up compressor or motor or even low voltage can also mean a motor hums but won't start - we give links to those diagnostics in step 2 above. See CAPACITORS for HARD STARTING MOTORS Condensate pan switch lockout: an attic or other air conditioner air handler condensate drip tray or drip pan located under an air handler is installed to catch air handler condensate leaks if the normal condensate drain system fails. Some condensate pans have their own separate overflow drain (a proper installation) or share their drain with the normal condensate drain (an improper installation).

But on some air conditioning air handlers the installer may provide a condensate overflow pan switch rather than a separate pan drain line. In this installation the switch is designed to turn off the air conditioning system if it finds condensate water in the overflow pan. The idea is to shut down the air conditioner before there is a more costly leak into the building insulation or ceiling. Condensate leaks into the condensate pan can shut down the air conditioner. In tracking down an air conditioner condensate leak, I found that the the condensate pump drain line, a small-diameter PVC pipe, was clogged with water mold. That was why my air conditioner wasn't kicking on. It would of ended up costing at least a hundred dollars just for a service tech to fix something as simple as that. I had to take the pump apart and clean it. I took off the PVC drain line coming out of inside air conditioner and blow and clean it all out too. - Jacob Behrends, FL The central a/c in my Florida home (in late July) would not turn on and the temp in the house was well above the preset temp of 78.