central air conditioner not cooling

I've been reading deja articles for hours on separate days - but I would like some quick advice if possible. I'll try to keep the story short.
Moved into a condo; very old Lennox upflow heating/2-ton air conditioning unit. <900 sq ft open space (no bedrooms/doors)
The air that comes out of the registers is _somewhat_ cold - but not cold as I like it to be. As a result, I can only maintain the indoors temperature at about 78, no lower. I would like to get down to 70 if possible (outside temp 80-95).
It appears that the previous owner did not have an air filter where the air got sucked in by the fan... so I put in a new filter. Due to the way the unit is positioned (basically inside a closet) - I'm not sure if having a filter is causing a problem by possibly restricting intake of air.
There is no icing on the pipes at the outside condenser unit as I can see. The alum fins on the condenser unit looks ok, free of debris. I had a guy come out and fill it with a pound of R22, he said it was low. I did notice some improvement, I can go down to about 76 now, but still I would like to go down further to 70. Am I asking the unit too much?
What else can I check to narrow down the issue. From reading some posts, how do I check evap coils (this coil is different than the condenser right?) & condensor/coil water drain (not sure where this is located)?
I realize that the AC guy is supposed to be doing this stuff for me, but to make a long story short I do not get to choose who comes by to diagnose the unit. In the event I do have to shell out money, I would like to be informed.
Thanks for any suggestions.
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On 27 Jul 2005 19:13:57 -0700, snipped-for-privacy@gmail.com wrote:

With a severe shortage of refrigerant, the low side can run in a partial vacuum. If there is a leak on the low side, air and moisture could have been drawn in when it was running low on refrigerant. Without fixing the leak and evacuating the system prior to adding refrigerant, the air and moisture wreaks havoc with the system.
You might not be able to choose which tech the contractor sends out, but you certainly can and should choose a different contractor!
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-john
wide-open at throttle dot info
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try evacuating for 1 hour and recharging the CORRECT manufacture's recommended amount of virgin R-22 freon
also, comb out all mashed-in places on condenser coil and evaporator coil
with unit off, clean condenser with 1/2 Alki-Foam, and 1/2 water mix leave on 5 minutes, rinse with hose http://www.virginiakmp.com/Spec/AKF1.pdf

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In alt.home.repair on Thu, 28 Jul 2005 03:02:58 -0400 "papaya"

I've tried that with what we call a butter knife, an all-metal knife with a slightly serrated blade that isn't sharp enough to cut meat.
And also a small screwdriver iirc.
And I bought a fin comb, and tried that too. One with several sides for different numbers of fins per inch.
It still seems to take forever. Is their a trick?
Should I use some sort of lubricant? What?
thanks..
Meirman -- If emailing, please let me know whether or not you are posting the same letter. Change domain to erols.com, if necessary.
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snipped-for-privacy@gmail.com wrote:

How much space is below the furnace closet floor? Lack of Return Air Grille Area could very well be restricting the airflow to & through the cooling coil!
Check thoroughly for hot air leaks from the attic down through the wall petitions to under the air handler! These are common problems I have found over the years of servicing A/C systems. If you have room put large return air filter grilles along the sides under the furnace closet floor, do so. This will allow you to have more open air return area for the lint loading of filters. (See Linked page.) If you can use the other return filter grilles, if airflow is then not adequate, remove the furnace filter.

Well, if your "Design Conditions" are similar to mine": 88-dry bulb, 73-wet bulb , around 49% Relative Humidity, then "a mere half ton 6,000-Btu/hr" window shaker with a floor fan setup like mine would get you to 76-F and to 50% RH even on high humidity days. Your unit is 2-tons or 24,000-Btu/hr, 4 times the capacity of mine! http://www.udarrell.com/airconditioner_current_temperature_btuh_charting.html
What do you want to bet that your 2-tonner is not getting anywhere near 2-tons of heat transfer from the indoor air to the outdoors! Also, it must not be reducing the humidity sufficiently or you would feel very comfortable at 76-F.
My 6,000-Btu/hr Whirlpool remote control room A/C only cost around $130.00 and cools well within the comfort zone around 920 sq. ft. on the hottest days imaginable, 112 Heat Index days! Am I a happy camper, you bet I am!
With the power disconnected check the blower wheel blades; if they are filled with lint then the evaporator coil is plugged and insulated too. No system should be charged with refrigerant until it is confirmed that the evaporator has an optimal heatload being absorbed by it!
The condenser may appear to be clean to you, but could be blocked between the fins and/or the fins cold be insulated by wrong cleaning methods such as using oil based detergents when it was cleaned in the past. (It is very old!) Both coils should be thoroughly cleaned with a good coil cleaner; the evaporator should be thoroughly cleaned with a good evaporator cleaner.
Only then, should the system charge be balanced: http://www.udarrell.com/ac-trouble-shooting-superheat-subcooling.html
Leave all, these jobs to a good tech! - udarrell
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Factors in the Correct Sizing of Residential Air Conditioning Systems -
Recommended Procedures for Proper Duct Sizing of Residential Air Conditioning
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If there has been no filter in your unit then for sure the evap coil is dirty. That being said, it does not explain the lack of cooling on the lineset or the air coming out of registers. You need a competent tech to come and check the whole system over. Could very well be a leak on an old system on the other hand techs who just "throw in a pound of freon" because they don't know any better are not helping the situation. Also the advice to " vacuum the system down and weigh in the charge" is useless unless you can find out where the system is leaking.
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