Over time, your central air conditioner may encounter a problem with its fuses. Rather than spend days fending off the heat while you wait for an expensive electrician, follow the simple steps below to replace one or more fuse. Before you take your air conditioning unit apart, it is imperative that you know what kind of fuse you will be replacing. To examine your fuses, look for a switch near the compressor of your unit. Before you open the compartment, turn off the electricity source of your entire air conditioning unit. Turn off the circuit breaker that controls your air conditioner. Once the circuit breaker has been turned off, turn off the switch in your unit. Open the door located near the switch of your compressor. You will see two cartridge fuses inside of this door. The fuses will have wires connected to both ends. Use your voltage tester to test the 2 wires that are coming out of the disconnect switch, situated on top of the fuses. You should test both terminals using your voltage tester.

Test the bottom wires also. No voltage must register after testing the wires. Only then should you proceed. Use fuse pullers to take out the fuses. Take a look at the amperage written on each. Most fuses have a 30-amp label on them. Also, check the fuses if they are the standard, fast or delay-rated varieties. Purchase a similar pair of fuses as the ones that you took out. Make sure that you check the new fuses that you have for continuity. This will ensure that the fuses will work properly in a normal, undamaged air conditioner. Sometimes, only one fuse has to be replaced at a time, but for convenience sake, you should also replace the other fuse. It is easier to remove both fuses at the same time. Use your fuse pullers to insert the new pair of fuses. It is very important that the fuses are properly positioned in their clamps. If the wires of the clamps are not appropriately set on the terminals of the fuses, your air conditioning unit still won’t work. To find out if you were able to replace your fuses properly, turn on the circuit breaker of your unit as well as the thermostat.

If the unit works efficiently, you’ve done a good job. For years, my A/C condensing unit has blown a fuse once, maybe twice a year. It's 27 years old now and blew a few fuses last spring. Now it blows a fuse every few days. So, I replaced a bad running capacitor on the compressor and replaced a leaking capacitor on the condenser fan motor, still blows fuses every few days. Dangdest thing is that it has a very respectable amperage reading - 20 amps on each leg (it's 220v) even when it's very hot (105 degrees outside) and the fuse only blows in the evening when the temperature has gone down for the day! hvac unit rentalI thought that maybe it blew a fuse when cycling off and on, so, I tried just operating the A/C manually (turning it off when the inside temp was comfortable and on when I wanted some cooling) - still blows a fuse.replacing hvac units

I now wonder if the problem is with the fuse box or power supply. It is typical that after a day or two of replacing a fuse, the new fuse darkens - it still works, but can get quite dark. A blown fuse will be really dark and the nice clean copper is pretty scorched. I cleaned off the contacting surfaces of the fusebox and tightened the wires down. I'm now suspicious of a possible occasional voltage drop in our power supply. Wouldn't that spike the amps to my A/C unit and burn a fuse? ac air compressor for carA few weeks ago the power company installed a box to monitor power quality right outside my house. When I asked them what they were doing they informed me about monitoring the power and then asked me if I noticed lights flickering and so on. I thought I might monitor voltage last night to see if I might catch a drop (wishful thinking I guess). But anyway, just using a 120v receptacle, the volts were 120.0 volts to begin with, 118.8 volts when the A/C came on, went down to 117.4 volts, then ranged between those last two numbers 'till I turned the A/C off an hour later.

Then the reading was 120.9. First thing in the morning, the voltage was 123.0 volts So, there's quite a swing in voltage - I imagine that's normal, but I don't know. I'm up a hill, at the end of the power line in a city area. Here's the particulars of my A/C condenser - it's a 1985 Sears 3.5 ton (NCABA42AB01) - full load on condenser= 21.5 amps time delay fuse called for is 30 amps and that's the fuse I keep replacing. Anybody have any ideas - poltergeist, maybe? Update: It just blew a fuse again - mid day this time. I noticed that the fuse box was really hot - I measured it with an infrared thermometer - 220 degrees F! The condenser unit was buzzing, only one fuse blew - the other looks fine. I'm thinking I need to replace the fused disconnect. Long-term darkening of a fuse on a high-draw circuit like an AC is not unusual. However, darkening as quickly as you have described means the fuse is operating right at its limit for too long. The first thing I would do is call an electrician and have the fuse replaced with a breaker.

At least that way you don't have to touch a hot fuse to replace it. They may also find a problem with the wiring (corrosion or a break) that could explain your problem. Next is I would buy/borrow a multimeter that has an amp clamp on it. Measure the current used by various parts of your system (blower motor, compressor, condenser fan) as well as the main power feed to find out how much current you are pulling. This may help you identify which component is causing the problem. I would say look for a loose wire or a wire that is partially bare that is touching metal.check your ground wire and make sure that you have a good connection. Well I have a similar problem but with a brand new installation. Worked fine for 6 months then breaker tripped. Reset then 30 amp fuses blew. Replaced capacitor, still blew the fuses. It could be the relay that switches from start leg on the cap to the run leg on the cap, if the relay contacts are badly burnt it stays on the start leg, 5 volt drop is nothing I have worked in many areas that there is only 112V/ 224V with the motor starting and not having the phase corrction it cant make speed draws a little more power and also usually dosent cool as well (other than a loose