You can't without specialized tools. Best you can do is call another servicer for another diagnosis/opinion, although I wouldn't say anything up-front about ABT's diagnosis so as to insure the new guy finds it himself.

What about the freon level. He indicated that the freon level is low. I could get the report and compare it to the full capacity f the unit? ABT also did the serivice last year. I could get a report of those. Thanks.

A tech who sets aside self-interest by recommending replacement instead of costly repairs is golden! Replacing Freon is a short-term fix unless the leak can be found and closed. At 21+ years your AC is likely in its final days, more so if any owners skipped tune-ups. Google your model’s typical life span. Newer units may be quieter, more efficient and use less energy. I wouldn’t replace it until it actually starts to underperform, but use this time to research replacement brands and installers. Avoid an emergency install if you can! Our AC died one sweltering August while my kiddo was housebound recuperating from surgery. No decent local installer had my ideal model and size in stock, so I had to compromise. These days AC units may be in even shorter supply like so much else.

I disagree with many of the responses above.

I wouldn't waste any money "diagnosing" or repairing such old equipment. The essential diagnosis is that it's old and beyond the expected useful life. Your money is better spent with a capable HVAC contractor with good references, who can remedy the problem by installing new and properly sized equipment. Good luck.

Servicers check refrigerant level by connecting/reading pressure gauges. The unit's specifications label may reference it by weight (lbs and/or ounces) and the only way to check that is by pulling the refrigerant out of the unit for weighing it. The charge needed in a given system to attain proper operating pressures may vary depending on the length of the lines between the indoor evaporator and outdoor condensor, unlike a window unit or automobile on which the layout is a fixed factor.

Did the tech say how much refrigerant is needed and provide a price quote?

He was said he could not tell but the pressure was down. I am having ABT send me their notes so I can compare the notes from last year vs this year.

I don't neccessarly agree nor disagree with above advice but I didn't see an answer to your question " How can I check up on his story? Should I just get his report? I have a general principle of how AC works, but I don't have the background. What should I be looking for?"

There's no way for you to measure the level but you can do a couple of things that are actually better than knowing level. After unit has been in operation (cycling on and off as it is supposed to over 2 or more hours), touch large copper line between outdoor unit and building. It should at least as cold as the warmest drink you would drink without adding ice. Preferably it is as cold as a drink fresh out of fridge or with ice in it. If large line is exposed to air,it should be sweating or very near sweating on humid days. I wouldn't worry about freon if that's what I found. I said I wouldn't worry about "FREON",that doesn't mean everything else is as it should be "OR" that freon is definatly at full charge. It might very well need a touch of freon after one or more other issues have been addressed but for now freon is ok.

Another thing you can do is use and accurate thermometer to record temp of air being drawn into indoor unit (basiclly room temperature) but reasons I won't get into, should be tested at intake grill. t Record temperature at any discharge grill and subtract that number from intake temperature. Any less than 17*F difference on a unit from the 90s and back will have to run continous on a hot day and might still not cool enough. 20*F is what i would expect so anything more would make me happy dance. As with first test,this doesn't mean performance can't be improved,it simply means freon isn't likly an issue for the moment. If you truly do have a basic understanding and are hungury to know more about" checking up on" a preventive maintenance service,we can talk about it.

I hope that's a little closer to answering your question than advice to give up and buy a new one.

Is the system functioning (cooling) adequately? If so, leave it alone. If it's low on refrigerant, cooling should be impaired and/or you should see icing on the line coming into the condenser (or icing up of the evaporator coil).

If you can confirm you have a leak, then you should look at replacing the system. At that age, its R22 which is horrendously expensive to "top up" and leaking R22 is just plain awful for the environment.

Ask for a written repair quote. If they refuse then I suspect it is a scam. If the refrigerant is low you would notice the AC would not be cooling as it did in the past.

The second year, they said there is freon level has dropped, so he suspect some sort of leak. He indicated that he can top it off but the issue is that if there is a leak, it may need topping off again. Because the unit is from the 90's, it may be better to replace it than repair.

Based on what is being said it simply sounds to me this tech is planting seeds of doubt more along the lines of *because the age of the equipment is old.*

I made a repair to a 2005 run of the mill builder grade Lennox AC yesterday. The problems were all electrical, upon starting the unit surprised the Freon (R22 variety) was fine.

Later that same day different house different unit... 2012 Lennox builder grade model the Freon (R410a variety) was low.

That being said, some things can mimic a system being low on Freon... so just looking like it's low and being low is two very different things.

Calling a tech of a company is dangerous way of doing things because that tech is primarily put under the wringer to sell these days. They do it a myriad of ways. They will never get called out on this when the system is older especially if the unit is R22.

What's the difference? I am a Texas licensed HVAC contractor.

The tech is looking for his next commission "sales" check. The company he works for is looking for work to keep install crews busy. The busier they are, the more likely the company owner makes a profit.

How hard is it for a single one man shop to turn a profit? Yes, I am in this for profit. Stop kidding yourself. No one does this for free.

You want to replace something that needs replacing. You want to fix something that needs fixing. Do the temperature drop tests as stated earlier up in the thread. If in range of a 15-20 degree drop. The system is likely ok. If only a 15 degree drop, it's not as good as it should be but still within specification.

I service the Katy, Texas area. Open Memorial Day.... making it one day to remember as it were.