Repair or Replace
Q1: Should I repair or replace my 14 year-old Carrier 10 SEER 5 ton unit in North Central New Mexico? (Model 38CK060330)
It is intermittently tripping the circuit breaker. When the breaker is reset, the unit runs for a few seconds, stops for a few seconds, then trips the breaker as it trys to restart. The technician replaced the small 24V line leading from the house to the compressor, stating that by moving it, he was able to force the compressor on and off.
A few days later I came home to find the breaker tripped again. This time the same tech brought a (compressor?) tester and says that, while the compressor checks out OK, he can't tell if the high pressure switch is bad or the wiring associated with it. (When bypassed temporarily, the unit runs OK.)
The cost of replacing the switch is about 25% of the cost of a new 13 SEER compressor, but he says the old 10 SEER inside coil would have to be replaced, too. Q2: Is a new "A Coil" replacement coil required, good practice or both?
Q3: If I elect to replace the entire system, would a new furnace also be in order? If so, any recommendations on AC? Furnace?
Q4: All this for a bad switch?
clean the condenser coil! No I would not change compressor. Verify that previous servicer did'nt overcharge unit. Find a new servicer, the problem you describe should have been fixable in 30 min..
A1: I'm a bit surprised this tech couldn't diagnose the problem the first time and fix it. I'm also surprised he didn't do a more comprehensive system checkout while there the first time.
A2: However, he is right, the unit and indoor coil are a matched set.
A3: Don't know. You never said how old the furnace was, how efficient, what fuel it uses, how much you run it, and what fuel costs are in your area.
I would get a second opinion, from someone else. If you feel they are competent and you are facing replacement, let them give you quotes. Make sure they give you various option quotes from 13 SEER on up, so you can run the numbers on long term cost-benefit. Then come back and post the various options to the pros here. Their opinions would help a lot in determining what's the path of least pain.
Follow-up for Q3: The furnace is a 14 year old Carrier Weathermaker 8000 natural gas unit. It runs October thru April. The gas bill for February was $171 (149 therms @ approximately $1.15/therm including taxes, fees and surcharges.)
Regarding the AC: Vendor 1 has provided two quotes. The first quote involves keeping the furnace and replacing the AC with a 13 SEER 5 ton Bryant. The condensor is model 123ANA060. The coil is model CNPVP06024AAU.
Vendor 1's second quote is for a new furnace and 15 SEER AC. The furnace is an 80% efficient 135,000 BTU Bryant model 312AAV060135. The AC condensor is model 165ANA060. The AC coil model number is unstated, replaced with a comment "matched cased."
The bad news involves a second opinion on the diagnosis from Vendor 2. The technician says that the compressor runs and that pressures looked good, but it "wasn't moving coolant." (Q5: How did he determine that? Q6: If it wasn't moving coolant, why did the AC still cool the house in those intermittent periods when the breaker doesn't trip?) By the way, the technician temporarily replaced the smoke-traced contactor and condensor to get the compressor to run.
Q7: Do I need a third opinion or should I continue to pursue quotes on a 13 SEER Puron Carrier system with a new furnace?
Follow your gut and start over and get someone who can do a better system checkout. I would not make any other decisions until you get that information. Feel free to (re)post that information.
Until then and as food for thought, I may be wrong but I think that Weathermaker 8000 is already 80% efficient. Vendor 1 may be right - you may need to replace the furnace to mate with a higher SEER unit. The pros here can give you a better idea why Vendor 1 is recommending that but my guess is because the higher SEERs need a variable speed fan. If so, don't be afraid to ask about an upgrade path to mate with a higher SEER unit. Carrier still sells that unit with a VS fan, so that may be possible. The pros here might be able to give you some ideas if doing that to an older system vice replacement.
I have no idea what your electric rates are but you should also consider a heat pump should you decide the a/c needs replacing. A heat pump might give you better heat economy than your current per therm cost (down to a certain temp) and be a good hedge against rising ng prices.