i does not mean there is a leak somewhere. i have 368 janitrol A/C's i take care of every year and sometimes you run into one or two a year that just need a charge of refridgerant. you can also tell if the system has a leak in it while you are charging the system. the biggest part of the time i find a leak, the leak is coming from around the schrader valve. if you are having a leak you will have the problem again.

 

To DeckedoutF150; Do you have a C&D schrader tool? This is on of the best tools made for HVACR service. I've had a couple of other brands but they don't even come close to this brand. You can replace the Schader and not loose more than a thimble of refrigerant. PS they will not work on vehicle hi-side schraders.

 

What is the square foot of the area it is trying to cool...and what is the tonnage or btu of the unit?

 

Nobody mentioned about a dirty condenser coil, a more likely culprit.
Yes it is best to leave an A/C system on any time the night time temps are above 55 - 60 degrees. less humidity infiltration into the space. High humidity does more to raise your cooling bill than temperature. Cool air holds less humity.
System are size based on heat load not a degree an hour. Manual J and Manual M, heat load calculation books.
Air conditioner compressors do not need to be started like your car A/C. they are a sealed system. no air or moisture can get in. Car A/C are slghtly differant. They use a open type compressor, meaning the electric motor is not sealed within the refigeration system. Car A/C have shaft seals that can start to leak from not being lubricated. Also if you start you A/C when it is too cold out, damage can occure from liquid refrigerant in the compressor.
If a system needs refrigerant, it has a leak. I would like to know how you tell a system has a leak just by charging the system? Sharder valves need their caps, make sure it has a rubber seal or the cooper washer in the brass hex type caps.

 

well when you are charging system you got to shut the valves off on the manifold to let the preasure balance out. i usually charge the system a little then shut the valves off on the manifold to see if it is at the proper preasure. let it set for about 10 to 15 min and see what happens. also if you charge the system and it never seems to reach the proper preasure then you have a leak. the schrader valve you can tighten them some times but if not you have to evacuate the system and install another schrader valve them put a vacume on the system and recharge it. just putting a cap on the schrader valve or making sure the cap has a new "O" ring in it will not stop the problem. i have probly 10 units at work that i have added refridgerant to at the begining of the season and not been to since. also my system at home needed some R22 and i added to it at the mid point of the season and have not ahd to since. the problems i run into most are coils that are very dirty or a very dirty air filter. these could do anything from making the system freez up to not having enough air movement. i also run into alot of A/C breakers tripped in the apartment and its not cause of low preasure its usually cause the resident palys with the thermostat. if your coils are clogged your preasures will be off from what they should be accourding to figuring it on superheat or the 30 plus rule. cooler days are the hardest to figure out.

any HVAC guy that has been in the bussiness for a while should know to check for a leak when chargeing the system. its also pretty obvious when the schrader valve is leaking, the cap seems to just want to blow off into your hand.

 

DeckedoutF150,
If your pressures do not add up on charging does not mean a leak, what if your metering device is restricted, or you have a power element on a TXV slowly going bad ? the sure fired way to tell if a system does not have a leak before you charge is a micron guage.(digital read out or analog) If you can reach 500 microns, and hold within 15% it good. If the system has refigerant in it(under 20 psi static), use nitrogen and pressurise the system to >100 psi and go over the system with a Inficon D-Tek. Finds the leak every time.
http://www.inficonservicetools.com/r...gerant_339.cfm
I will call your BS about putting a cap on it will not solve the problem, came across a walk-in cooler with a 1/4" service port, no schrader vale in it, has held with no leaks for ten years and counting. Scharder valves are not intended to be leak free with out a cap.
I have been around long enough, worked on everything from fractional sized air conditioners up thru 120+ ton chillers, also reach-in to drive in coolers and freezers.
Hint of advise, don't use rules of thumb to determine your problem, prove what the problem is. Newer equipment does not work with the old rules, most manufactures give alot tighter specs. on the temperature and pressure readings you need to have to properly operate. Not trying to pick a fight, I have seen too many guys in the buisness just winging it.