So, you turn on your air conditioner to cool the place. The place does not get cool. So, you call the repairman.

He shows up. He checks your system. "I have bad news for you. Your compressor is bad," he says. "You need a new condensing unit. I can install it day after tomorrow, for $1500."

You, being the clever consumer, are suspicious. "Show me," you say. So he does. The cover is off the unit and you can see the compressor. He cycles it on. You hear and see the fan start, but quite obviously the compressor is sitting there and not running. Well, whatcha gonna do? It is not running. Must be bad. So, you sign the work order, and start figuring where you will cut back to pay for this sudden and expensive repair.

Well, congratulations, sucker. You have probably been had.

Compressors do go bad, of course. But most of the time, when the compressor does not start, it is not the compressor that is at fault. So, for your information and edification, here is my list of the things that keep a compressor from starting, ranked more or less in order of frequency of occurrence, with some indication of cost and time to make a proper repair. I will stick with those cases where the fan comes on and the compressor does not; if neither fan nor compressor runs the problem is obviously electrical and easily diagnosed.

Now, if you decide to try any of these repairs yourself, be certain you disconnect main power at the breaker panel before starting.

The most common reason that the compressor will not start is a failed starter capacitor. This part, depending, costs anywhere from $6 to $25 and can be purchased over the counter at any supply house. The skill level required to change it is low. Anyone can do it, if they properly identify the part and own a screwdriver and a nut driver. Some electrical tape and/or foam rubber helps here too. The capacitor is a metal can (usually silvery, but possibly painted grey, dark green, blue, or black)located in the electrical box inside the condensing unit. It will have two or three terminals on top, each with four mounting lugs, with wires going off to the compressor and (if three terminals) also to the fan motor. It will be held in place with a strap.

The easiest way to diagnose this capacitor is by swapping it with a new part. If you have a capacitor tester, you can use it. Otherwise, just get a new one. Remove the old capacitor (do not lose track of what wires go where) and take it with you. The supply house clerk can help you get the proper new part.

When installing the new part, which may be a different size than the old part, the foam rubber and electrical tape may come in very handy.

The next most common cause of a no-start is a corroded and broken electrical connection. This may occur anywhere on any of the wires associated with the compressor, but often is found at the connections to the compressor itself, under the cover on the compressor. The skill level to fix this is low. Parts cost is usually under a dollar but may run more if it proves necessary to replace any wires. Pop the clip that holds the electrical cover on the compressor off, then remove the cover. If there is a faulted wire, remove it from the electrical box, and gently work the corroded connector off the terminal. Be careful here; the terminal may also be corroded and if you break it you may find yourself with no way to make a connection to the compressor (which would require you to replace the compressor). Get an appropriate crimp-on terminal (auto parts store, Radio Shack, or Walmart), clean up the wire, crimp the new connector onto the wire, and put it back on the terminal on the compressor.

The next most common failure is with the thermal protector inside the electrical cover on the compressor. The skill level to repair this is moderate, and to replace it the skill level is low. However you might have to repair it because you cannot find a replacement. Typically, wires corrode off here and you will find it necessary to solder on a new connection. Use appropriate techniques (and rosin core electrical solder - not plumbers solder) and have at it. If you can find a new part, it will cost less than $5, typically, and saves you having to solder an old part.

Next on the list is any sequencing relays that are in the unit. These are not commonly found, but exist in some units. The skill level to make this repair is moderate to high, mainly based on the requirement to properly diagnose the problem. The skill level to actually swap the component out is moderately low.

There may be an electronic controller in the unit rather than sequencing relays. The skill level to diagnose this is high, and the skill level to replace it is moderate.

Next is the compressor itself. The skill level to diagnose this item properly is moderately high. The skill level and equipment requirements to replace it are very high.

Next on the list are any pressure or temperature sensors that may be present in the system. The skill level to diagnose and replace these is high, and the equipment required to replace them is moderate to very high, depending on the details.

Now, in some units with a lot of age on them, the compressor may run just fine when it runs, but is unable to start against the load of the system. For these you can obtain a hard-start kit. This basically is a device that stores more energy and, when the compressor is told to start, shoots more current into it for a second (gives it a "kick in the pants"). This overloads the compressor and if sustained would burn it out, but it is not sustained. Besides, when it gets to this point, who cares if it burns out. It won't start anyway.

The hard start kit costs about $40 and will often do the job. Of course, in this case you will probably be replacing the unit in a couple of years, but that is a couple more years for $40. Diagnosing this problem correctly is a fairly high skill thing. Installing the hard start kit is a moderate skill thing.

And that is it, more or less in order. As you can see, a compressor failure is a moderately low likelihood in any given case. The most common problems are things that just about anyone with a basic competence with tools can fix.

Jim Locker holds advanced degrees in physics, has designed and developed computer systems and software for over 30 years, and was a landlord for 20 years running up to a couple of hundred properties. He presently works as an independent computer systems consultant and works for Just So Software, Inc. whose site is here Article Source:

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