My air conditionaing unit booklet includes three different reference numbers. They are as follows: 38CKB(N), 38CMB, 38BRB Split-System Air Conditioner. Do the numbers represent the furnace, top floor unit, and bottom floor unit? If so, what number would I use to locate the unit that needs the compressor (top floor)? Also, what is the cost for replacing a 3.5 ton Carrier compressor?

I would get the part number right off the compressor inside the unit. Many times during production the compressor brand or model number changes.

Cost of replacing a compressor varies depending upon weather it is a burn out, needs additional parts (capacitors etc) replaced. The area you live in and the labor rate.

You will probably be better off replacing the entire outside uint since the cost of replacing a compressor alone can be quite expensive and with a new unit you will get a 5 or 10 year warranty.

My air conditionaing unit booklet includes three different reference numbers. They are as follows: 38CKB(N), 38CMB, 38BRB Split-System Air Conditioner. Do the numbers represent the furnace, top floor unit, and bottom floor unit? If so, what number would I use to locate the unit that needs the compressor (top floor)? Also, what is the cost for replacing a 3.5 ton Carrier compressor?
Carrier labeling using the "38" refers to the outdoor unit. Depending on why you are replacing compressor depends on if you should replace compressor or entire system. I agree with Hvac1000... sometimes it is not money well spent on a compressor out of warranty. And if you are getting compressor only replaced make sure it is with a valid company, there is a lot of "responsible" work to do when replacing compressor right.

My air conditioner is not working. It was diagnosed today and the technician determined the compressor is out. He recommended replacement. The quote is $2300 including labor and part. The unit is a 3 ton unit. My hour is 10 years old and unit is our of warranty.

My air conditioner is not working. It was diagnosed today and the technician determined the compressor is out. He recommended replacement. The quote is $2300 including labor and part. The unit is a 3 ton unit. My hour is 10 years old and unit is our of warranty.

I answered your single post. See comments above which pertain to your situation.