Yep, a leak I put a 10 oz can in last July 3, and the system worked fine all the rest of that summer. That time the A/C was just low, not "too low" and it was still cooling, just not as much as it should. The additional (without gauge) refrigerant brought the delta Temp up to specs. The trouble shooting of no clutch engagement led me to just add another 10 oz can to see what happens. The engine was running with the A/C switch "on" and it took only 10 seconds of the fill (these cans can take up to 10 minutes to empty on a nearly full system) for the clutch to engage and about 3 or 4 minutes to empty the can. I'll let it run this way for a few days and see what happens (it is cool here in NJ right now - in low 40s this morning). If it holds for a week I'll just top off using a guage and some anti leak. If I can get the car through the hot weather of 2013 for under $50 invested, I'll take it and worry abvut next summer if the car and I are both still around. Both of "us" are Senior Citizens. Up to 2009 I had always taken my purchased new cars to a shop to have the A/C serviced. I have kept all cars purchased new for at least 10 years, the 2004 is obviously coming up on 10 years - so new car is on the possible solution list. A 1999 Mazda was my first time adding refrigerant myself, it worked out fine there too - also just added a can to increase cooling, and it worked. I traded that car in before much of a test on the pump-up, but I did keep that car through that summer that I added the refrigerant.

Keep in mind that air conditioning moves heat from inside to outside, at a specific rate as per the BTU capacity of the system. It's constantly fighting against the heat load that's generated inside the house by cooking, lights, use of appliances (hair dryer, etc.) and electronics (computers generate heat) ... and heat that radiates in through walls and roofs heated by sunshine, windows, doors, etc. Other variables are involved such as humidity levels (squeezing moisture out of the air requires removing heat but the effective temp of the air doesn't drop ... latent heat). Units are sized to exceed the heat load under "normal" conditions so the temp inside the house can be reduced. There's a "balance-point" at which the indoor temp holds steady, the heat load exactly matches what the system can pull out. If the heat load exceeds the unit's capacity, as may happen during extremes of weather, the indoor temp will increase, although it will still of course be cooler inside than out. Setting the thermostat cooler will not have an effect in that situation ... it won't make the system run "harder" to remove more heat*, the system is either ON and removing all the heat it can, or it's OFF and removing none. A way to determine if the unit is functioning within normal limits is by checking the intake air temp (at the filter grill) and the output air (at the closest register). There should be a reduction in temp of about 16F to 20F ... which is the heat removed as air flows through. If the differential is less than 15F (more or less), then there may be a problem. Checked mine (5-ton, 60,000 BTU system) a few mins ago, 78F in, 57F out. *Except maybe in the case of a two-speed system if it's running on low speed and setting the thermostat cooler triggers it to high speed ... but in such a situation the system would likely already be running on high speed.

Here are the model #s: A/C Before- Goodman CK36-1A, A/C After- Carrier 24ABB336A340. Although, for some reason when I put my serial number in Carrier's warranty website, it said the model number was 24ABB336A003 (don't know if that's a problem). Coil Model Before- unknown, Coil After - Carrier CNPVP3617ALA. I don't know if they did a calculation to determine the size or if they just went with 3 tons because that's what we were replacing, and it had worked fine. Is there an inexpensive tool to measure the air flow out of each register or do just HVAC people have those? We know we had dampers in at least one duct back when we first moved in. Do those ever get messed up in the process of replacing the coil?

Not quite the same thing but I changed the door on my KA dishwasher and, when I ran it after the tech left I noticed that the heating unit was on, and it did not cool down. I opened it etc. but I still felt the heat on. I called our electrician (neighbor and friend) and asked if it would burn out and catch fire. He told me to throw the breaker. I turned the breaker back on the next morning to see if it was still heating and it was fine, and has been fine ever since. Maybe the unplugging will reset it, just like throwing the breaker did for me. Our electrician said that with a lot of the new electronics sometimes it needs to be reset, just like a router.