Location?...HP system with air handler or AC with furnace?...15-16 SEER complete system seems to be the sweet spot for best value and efficiency...

IMO

What are the sizes of the first and second floors? Are you saying you have a 3 ton condenser for upstairs, and 5 tons of cooling for downstairs?

What is the problem with the current American Standard system? Did you get a quote for repairs?

Our home is two story 3500 sq ft, larger bottom floor than upper. Both hvac units are in the attic. We live in a warmer temperature area of Los Angeles. The a/c runs on a two programmable thermastats controlled by a home automation system.

The 3 ton upstairs unit is a Carrier that was installed in 2010 which I believe is a two stage unit. The 30yr old Lennox was quieter.

Now the 5 ton American Standard Allegiance installed in 2002. It stopped cooling and the hvac company that installed the upstairs unit came to repair. According to the repairman (who I like) it has a leak and needed a hard start to get it cooling again. 5 lbs of refrigerant was added and it's working ok. Not perfectly AND the outside temperatures are in the high 80's today.

The unit had it's six month maintenance and filter change in April. It lost all that coolant in 5 months. He recommended a new condenser and coil. I have the complete estimate. It's over $5700 for a 14 seer unit. He did not recommend nor quote a new furnace. Can I up this unit to a 16 seer for more efficiency and lower utility bills? It's the unit that runs more often due to being downstairs and cooling the kitchen.

Is a Carrier Puron unit the optimal choice?

Air handler or furnace? Identify and provide brand and model number.

IMO

My first suggestion is to find a HVAC contractor who is interested in finding and repairing the leak. The guy you have is only interested in selling you refrigerant, coils, and condensers. He should have done this first and then decided whether it makes sense to fix the leak or not.

A 5 ton condenser should be large enough to cool the entire house. If the ducts and air handler was in a conditioned space you could probably get away with 4 or 4.5 tons. You need to find someone who will do a load calculation rather than just replacing what you already have.

I would inspect the duct work in the attic and see if it needs to be fixed or upgraded before spending money on a more efficient condenser. You will most likely need a variable speed air handler in order to reach a SEER 16 rating. How much money are you spending per year on cooling the house? You should look at that before deciding whether you should invest in a more efficient unit.

Carrier/Bryant makes good equipment, as well as Trane/American Standard. It is disappointing your current AS only lasted 13 years. It could have been due to initial installation problems. Trane/AS, as well as others, have had problems with failing coils. The new coil design materials are greatly improved.

Let me look for the original invoice with all the info. The tech told me that the coil had "oil"? on it indicating that was ready to fail as well. It wouldn't start without him installing a hard start --whatever that is. I'm not pleased that I wasn't forewarned before incurring repair bills. I might have held off doing the "fix". He said this should keep it going for a few more months. Yes?

The furnace is a 100,000 BTU 2-stage 80%(Model AUD100R960K) with a 14 seer condenser (model 4A7A4060A1000A). I spoke with American Standard today and its definitely out of warranty. Am Standard did confirm that it's a Freon condenser and not Puron. Ironically, I must stay that today it's working like a champ. I guess the shot of 5lbs of Freon did the trick-- for now!

I was satisfied with the Carrier installer and they have continued to maintain both systems. The original installer on the Am Standard changed hands and became slimey. That's why we bid the second system with a new company when we did our remodel. The duct work was upgraded and changed both in 2002 (when the unit was moved up to the attic) and again in the remodel of 2010.

How large is the second furnace? Whatever it is the combination is over sized for your climate. I thought load calculations were required in California.

Mike, I really don't know how i would possibly figure out load calculations. I left that up to the last professional who came to us via our contractor. Our upstairs unit is 3 1/2 tons at 95,000 BTU. It has a 14 seer compressor is made by carrier.

Refrigerant commonly leaks out of the A coil which is not repairable. You might get it replaced if it leaks right back out.

Thank you Mike, air-conditioning is my much bigger concern here not heating--- it doesn't get that cold here, you're right. We also have inadequate insulation, especially compared to other parts of the country. These are not two new systems. these are systems which of been replaced individually over time .

A different HVAC contractor just left and he said that load balancing is done in all new construction, but we aren't ripping out and starting from square one. We have a lot of windows-- only a few double panes, wood construction and live in a hot area of L A It's not about our need for heat. It's all about the a/c.

That is the point I am trying to make. You live in a climate that has mild winters, yet the furnaces are grossly over sized even for a house in a cold climate. This is red flag for any HVAC contractor who would do this.

I don't understand the comment about load balancing. Does he mean the equipment is sized properly?

How many days during the year does the temperature go above 95 degrees?

Your furnace appears to be XL80, a 2 stage furnace with a conventional blower with 5 ton rating. You should verify this. A badge should be on the furnace near the control door. If correct, I would have high stage on that furnace disconnected. Because the blower is conventional you are limited to a correctly sized 13-14 SEER AC condenser with matching evap coil. If you don't already have one, I would add a pleated filter media cabinet.

IMO

Mike, there are at least 4+ weeks of temps in the 90's and 100's. That can vary from month to month. We need the a/c quite often-- from a spring burst through fall.

Tiger, yes, it's definitely a 2-stage. We spoke with someone in depth about what we have and he is going to check which seer level we can use. He said that we can upgrade the furnace if we want the 16 seer, but he will send us quotes using different equipment. We are empty nesters who love our home, but I don't know if we will remain here longer than 10 years. It would be nice to lower our power bills, however if we have to spend $6-7,000 more to do that, it's not necessarily a good financial move. Decisions decisions. How long does a furnace last?

You can not go higher SEER than 13-14 with existing furnace. If keeping existing furnace have dealer disconnect high stage of furnace. Add pleated filter media cabinet if you don't already have one.

IMO

Would that be an Aprilaire? We have that!

Yep....just fine!