Can you use the new refrigerant with the existing inside unit?

If so, what would be units that are compatible with my existing one?

My outside unit is a 3.5 ton unit, but I am going to need a 4 ton due to an expansion of an added room to the home.

Any suggestions would be greatly appreciated as I am widowed and disabled and have little money to spare, however living in Texas, air conditioning is a necessity.

If this is not a possibility, then any suggestions on which new unit to try to purchase would also be appreciated.

Thanks in advance for any assistance you may lend in my huge undertaking!

  • I have a 26-year-old Carrier 3.5 ton R22 unit. When it needs a new condensing unit (outside unit) I will replace the inside unit as well. (Our inside unit is the air handler, a/c evaporator with self adjusting expansion valve, and a natural gas furnace.) The inside units have a finite lifetime and it would not make sense to try to clean and modify the inside a/c unit to allow it to use the new refrigerant. Like you I will probably increase the capacity to 4 ton. Apr 13 '18 at 11:31
  • How old is your central unit? If your existing condensing unit will not handle the addition to the house, I do not think it makes sense to try to change the condensing unit. If the combined unit (condensing and evaporating unit inside) has five to ten years of life expected, then I would leave it alone and get one or two window units to cool the addition. Will your furnace heat the new addition? Where in Texas are you? Apr 13 '18 at 11:38
  • What is the square footage of your home ? 3.5 Ton unit works fine up to 1800 Square feet - I have a 1700 square foot home in FL with a 3.0 ton acdirect.com/…
    – Ken
    Apr 14 '18 at 5:38
  • My central unit is a 2005 model and is not the best in the world. Your post was most helpful. Apr 19 '18 at 23:03
  • 1
    I have seen several units that were changed from R22 fail in just a few years. Yes the evaporator was flushed but getting everything out of the line set and evaporator I believe is just about impossible so I won't modify a system that uses mineral oil (R22 and older Freon) the residue can cause early failure mineral oil and POE oil used in New systems don't mix. I believe the energy savings from a complete replacement will make up the cost difference in the long run because the components will be properly matched especially since you want a larger unit.
    – Ed Beal
    Dec 21 '18 at 15:23

Air conditioning systems must be thought of as just that, systems. If you get a 4 ton outdoor unit you must have a coil capable of 4 tons as well, often times I will upsize the coil slightly to get better air flow and a higher efficiency. Air flow is also a huge factor in whether or not you will actually get 4 tons of cooling in your home. If you have 3 tons of air flow and 4 tons of cooling you are effectively paying for 4 tons of cooling but only receiving 3 tons. The indoor coil is likely old and inefficient and will not match up well with the new outdoor unit in terms of efficiency. If you upsize the outdoor unit you likely will not have enough air flow to handle it. Your ducts are probably too small and your furnace blower may be too small. If you really can only replace the outdoor unit due to cost here are some suggestions. Make sure you have enough air flow. If you don’t, upsizing the outdoor unit will not help and just cost more money. Don’t pay any extra for a higher efficiency unit since you will not realize any of that extra efficiency hooked up to your old equipment. The higher efficiencies are only realized with complete systems. The old mineral oil will need to be flushed from the system since the new POE oil is not compatible. The metering device at the indoor coil will need to be replaced since it will not be compatible with the new outdoor unit. If you have capillary tubes as your metering device you will likely need a new indoor coil since it would be too costly to change those. Verify that your existing refrigerant lines are the proper size, many older systems had really small lines that don’t work well with today’s air conditioners. Getting quotes over the phone is never a good idea since there are so many factors involved. I could tell you a cheap price to get my foot in the door just to bump it up when I get there. That will likely exclude many honest companies that realize a price on the phone cannot be done. A cheap quote to just replace the condenser without checking the rest of the system for compatibility may be doing you a disservice. I would not automatically dismiss a higher bid as a scam but carefully compare all the details. And see what you are getting for your money.


Can you use the new refrigerant with the existing inside unit?

A process called flushing is done to achieve this - the inside coils (Evaporator) AND the lines that feed the Evaporator are cleaned out with a solution - it is also done with nitrogen. The flushing not only removes old refrigerant, but also the old oil which can be detrimental to the new compressor.

There are some caveats to this as pressures of the new refrigerant will be higher and therefore you will face the possibility of a leak and then need to replace the unit.

My outside unit is a 3.5 ton unit but I am going to need a 4 ton due to an expansion of an added room to the home.

[Do you really need to upsize your unit Sizing Calculator at this Link uses the J-Model Sizing Calculations][1]

Now here is the issue you have with upsizing your unit.

The inside unit is most likely a 3.0 / 3.5 ton evaporator and normally an orifice is what changes the performance capacity for the evaporator.

You will not be able to install a 4 ton unit and expect to have 4 ton cooling capacity EXCEPT you install an Evaporator that is capable of 4 Ton Capacity.

Also upsizing you have another issue depending on your unit and the piping originally done - you might not have the correct pipe diameter from outside to inside unit (called a line set) - in which case the line set will need to be replaced as well. (if they don't do this - you will have issues (a higher electric bill as well as wasted money on a 4 ton unit operating at 3 ton levels).

Here is my advice:

Replace both the inside and outside units with a new unit - and also the line set going from inside to outside unit - if you spend a little more money and get a 16 seer unit - there might be tax credits available, not much but perhaps enough to Just offset the cost difference. You can also look into the utility company and see if they offer credits for more efficient units. Some units can run on Gas lines - so the possibility is the gas company might give you a break (or the furnace for that matter gas/ electric they might give you a break for using a gas furnace - perhaps even pipe it up for you (they expect a customer buying gas instead of electricity.. crafty way to get new business. sometimes the state will give you a credit for an energy efficient unit.

Depending; you could get a little or a lot, now if you only get a little how does it sound worth it if you only get tax credits that basically is a wash out?

Your electric bill will be lower (how much depends on how cold you keep the house and how hot it is outside) but expect at least $15/month ($150/yr) aka known as Grocery money.

A Typical 4 Ton unit from a reputable AC place will run you about $5000 to $10,000 .. I have just replaced a complete unit / except the line set [3.5 ton] for a property in another state the total was $5400. If I had replaced the unit here in the home I live in the price tag would have been $3500. There can be big differences so shop around.

Here is what these AC companies like to do - they like to schedule to come out (they do have good reasons for this - but more on why you should not do that up front). That is the sales pitch and the pressure to sign on the dotted line as well as how many people you would be willing to have come out and give you an estimate of cost?

I would venture most people would have 1 or 2 come out and rarely a 3rd..

DON'T let them come out - just tell them you want to know the rough cost over the phone for replacing the entire unit Air Handler/ Evaporator , Condensing Unit and Line Set with a 4 Ton Unit. Get the rough prices and the brand and types of units - try to keep the same type of unit and SEER rating across the board with all of them.

After you get that rough phone quote (some might not be willing to rough quote - just go ok and move on) - select 3 of them that gave you a rough quote and have them come out and give you the complete written estimate from a home visit.

I called around many people would not quote anything over the phone and insisted to come out (I am sure I would have had the $8,500 to $10,000 quotes at that point) along with the sales pitch and the yes ok I will work with you and drop to $7500.. after getting my [3.5 ton] unit installed / furnace ($5400) an ac person told me I got a REALLY good deal and for what I asked for I should have been hearing $7000 and up and he was right that was what a lot of them told me. [1]: https://www.acdirect.com/ac-package-unit-learning-center-ac-sizing-calculator

  • Thanks Ken, my daughter is also disabled and a student and my son is just starting out on his own, I am sure that if they were able they would be the first to lend a hand. I love the idea of asking over the telephone! I will do this, I also found out that there are grants for people like myself and am attempting to avail of these. Your post was most helpful. Apr 19 '18 at 22:59
  • @RhondaHaddockNorthcutt glad I could be a help. On this site if a post is helpful we mark the up arrow, if a post was the answer for us we click the check under the arrows. So if you will please mark one or the other or both..
    – Ken
    Apr 22 '18 at 0:34

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