You can try the heating and air conditioning forum here:

http://ths.gardenweb.com/forums/hvac/

The unit put in was probably of builders(low) quality. They should last 10-15 years. I doubt is was a 50 ton unit. Maybe 5 ton in a house with 3500 sq ft.
You may have to replace the air handler due to compatibility with the new compressor. Figure between $5000.-6000., worse case scenario.
Ron

Sorry, yes, 5 ton. Our house is 2500 square feet. You are probably spot on that it is a builder low-quality unit. We figure 10-15 years with normal use for most people, but we use it far more than normal people I think. We have it on nearly 24 hours a day (on auto, 69 at night, 73 during the day)), year-round.

Is the compressor what's in the backyard and the air handler what's in the attic? I just want to educate myself a bit before calling a service company.

" Is the compressor what's in the backyard and the air handler what's in the attic? I just want to educate myself a bit before calling a service company."
Yes.
Visit some A/C sites and do some reading. An educated consumer does better then one who is not. As you meet with these A/C guys, ask questions. You will gain knowledge from each encounter. It would be better if you could do this before or after the summer season.
Ron

Is it possible to replace just the compressor? Since that is what is making the horrible wailing, I have to assume that the whole *system* doesn't need to be replaced, just that.

What would be your limit of repair costs where you think it would be better to replace? It's still cooling well at this point, but sounds like something is slowly killing it.

A service call now for preventive maintenance could result in your current unit in lasting years longer.

The wailing could just be a bearing on the fan or motor shaft. See if you can turn the unit off and go out and spin the fan blade.
Service call is a good suggestion. Don't even hint at replacing the compressor to the service guy. Let him diagnose it for himself. You could hint at the bearing issue.
Ron

The life of HVAC equipment is 20 plus years. The equipment we install normally has a 10-year all parts warranty. A 5-ton system could be as low as $5,500.00. And, location will dictate price.

Phillip

So, an update. As I type a new air conditioner is going in. It finally died on Wednesday night. It would turn on, but would pop the breaker 5 minutes later for power overusage (never had happened before). Then it would make noise but not spin. Scary. The blades were also rusted from years of sprinklers hitting it (backyard has since been remodeled when we put the pool in and that no longer happens) and the motor was bad.

We got an American Standard Empire Ultimate Allegiance 18 seer 5 ton. No idea what the seers means (dh knows, I guess the higher the better?) and 5 ton is what we had before. They are also replacing all the components in the attic (coil, etc) and are putting in a new thermostat. They only thing they aren't replacing is the furnace. It was $5000 more and we hardly use it - no need to replace it. We have a 5 bedroom 2-story house, 2500 square feet.

I guess it's a good thing in the long run considering how heavily we use AC but to save up for a year for my son's braces seems stupid now. We got a second opinion on Friday and it was MORE. I guess I'm bound to get ripped off no matter from what company because of where I live (South Orange County, affluent area although we are FAR from affluent - just bought at the right time in the 90's). $8000. Just lie to me and tell me I got a fair price.

snookums,

As a (perhaps comforting) datapoint for you: Our 5 ton heat pump died just recently. We ended up having a Carrier Infinity 19 seer 5 ton unit installed, including the outside unit, and the air handler, and a new thermostat (that from the looks of it is smarter than I am.) as well as new pipes connecting the outside unit to the inside unit. The total cost for this (leaving out the new steam humidifier, which hasn't been installed yet) is $7894.

So assuming your system is about the same quality as mine (and I think american standard is the same as trane; and trane and carrier are often recommended as the brands to install.) I'd say you did indeed get a fair price.

Although I would say you got the short end of the stick in that your old unit only lasted 8 years. My old system seems to have lasted 27 years before sputtering to a halt.

What is theaverage cost of replacing a condenser and evaporator coil in San Antonio, Texas? I have a 2.5 ton condenser unit with a 2.0 ton evaporator unit in the attic, which I know don't work well together. I'm looking to replace bothe units with the correct size. I have gotten a $4000 estimate, so far. Is that reasonable?

Have an old rental house with 15-20 year old Bryant...very small unit...House is only 1000 sq ft and one story. Unit looks like on last legs. What is right size for small one story In Indianapolis. What kind is best? What can I expect to have to pay? Know any good places to shop in Indianapolis? Thanks

My home's Air Conditioner stopped cooling. The technician says the compressor need to be replaced.
I
have Lennox unit, 20 years old. The price quoted for replacing with a
generic comparable compressor 14 seers, costs $3689.00. Is it
reasonable?

jaromeiginla33: Absolutely not. I'm doing my research as I need a new compressor as well and the part seems to be in the $650-$1050 range depending on tonnage and BTU, plus about $250 labor. I am also looking at how it is installed and if you can solder copper pipe you can do it yourself, then call an HVAC guy to cycle the freon(3 times) for you for $100.