Central Air Conditioning Repair Question

My AC went out recently, and I was disappointed that my Home Repair books (which are usually real good) have nothing to say about what to do. Does anyone know of a checklist that I can go thru before I call a repairperson? I hate to miss something obvious and then have to pay thru the nose for a needless repair bill.

My system is the type with the compressor and fan outside, and I’ve already checked the fuse box and replaced the fuses*. I also cleaned the filter, just in case. The fan still comes on, but no cold air. Anything else I should check for before calling the AC guy?

*Bsideds the circuit breaker, there is a dedicated fuse box right nect to the fan unit outside. It has 2 slow-blow fuses in it-- whenever the AC went out in the past, replacing these fuses fixed it.

Do you get any air blowing through the vents at all, or just no cold air?

Unqualified anecdotal drivel and WAGs follow:

AC deals with refrigerant which (I think) are classified as hazmat. The reason is you’re not supposed to go poking around with refrigerant and release it all into the atmosphere. Really pisses off the greenies what with all that ozone nonsense. I ran into a similar proble when updating my car’s AC to the newer class of refrigerant–I could buy the install kit, but the Chilton’s manual said nothing about the AC system except: “Have a qualified technician do your AC system.” I got it done, but I felt guilty and did much repenting. I planted a tree and used a manual lawnmower for a couple months until I felt better.

ahem…Anyway, that’s my WAG about why your books wouldn’t have the info: you ain’t s’posed to do anything to it. That said, anytime my house AC failed it was because of a broken coolant line. Cars I’ve had saw the compressor fail due to age. In any event, the problem is the same: the coolant isn’t getting compressed.

First course: call the AC guy and see if recharging your system is an option. If that doesn’t work, take out your other wallet and look into replacing the compressor. If these things are anything like washers/dryers it’ll cost as much to repair as it will to replace.

About 6 years ago the compressor in my heat pump stopped working. It would make all the right sounds and the blower motor inside the house would still move air, but since the compressor wasn’t working, it wasn’t cold air. The tech arrived and gave me two choices. (1) Adding a booster for $75 to give the compressor a “push” that it needed to start running, but no guarantee as to how long that would last since the compressor was obviously on its last legs. (2) Replace the compressor for several hundred $$.

Because the whole thing was close to 20 years old, I opted for the booster. The heat pump lasted for another 5 years before it broke down again and I decided to replace the whole magilla.

Replacement will be around $2500-3000, (That’s what it cost to have ours replaced two years ago) so repair is probably a good option.

If the outside unit is running, you’re probably just low on refrigerant. Not a DIY project. If it’s not running, the possible causes are numerous. You’ve covered all the DIY-able bases of checking filters, breakers and fuses.

Central air is just one of those few things in a house that the homeowner really shouldn’t attempt to mess with. You either can’t get the supplies or parts, or you can readily transform “not running right” to “will never run again” by not knowing what you’re poking at.

If you’re skilled at things electrical, then see if when the Tstat calls for cool there is voltage supplied to the compressor contactor outside in the condensing unit. If not, there’s a field wiring or control board problem. If there’s 24VAC at the contactor coil terminals and the contactor isn’t pulling in, the contactor is likely bad. If the contactor is pulling in and the compressor isn’t starting, then it’s likely either a start or start/run capacitor, or the compressor is toast.

If you aren’t skilled in things electrical, disregard the above paragraph as the electical trolls beneath the bridge are easily angered and will bite the unsuspecting. Sometimes fatally.

The only time my AC quit blowing cold air it turned out to be frozen up. I think the filter was clogged and that is what caused the freeze up. If you can shut it off altogether for a day or so and stay somewhere else, it will thaw if that is the problem. The nice AC guy that came out never even billed me and I’ve kept the filter super clean ever since. You don’t really appreciate AC till it’s gone. Good luck with it.

Thanks for the adivice, folks. I’ll poke around a bit tomorrow and see if any of the suggestions pan out. Forturnately, the heat wave we’ve been having here for the last month or so seems to have subsided…


and another thing that you might consider checking:

My central ac compressor stopped working. I trouble shot and found that there was no control voltage at the thermostat. I went up in the attic to inspect the 24 volt control transformer and found that the drip pan under the evaporator was full of water. This raised a float switch which disabled the system. The root cause was that the condensate drain tube was plugged with algae. Cleaned the tube with a plumbers snake and siphoned the water into a bathtub. (If the float switch hadn’t worked, I’d be staring at a ruined ceiling!)