Yes, get a qualified technician out to take temperature and pressure readings. These and verifying that airflow is not an issue will tell you how much freon is in the system and where that freon is in the system.

Call the first company back and complain. If he added freon, what were the temps and pressures before and after? Why won't the unit shut off and why will it not get the temp below 79? What is the outside temp at that time? You got stung, time to fight back.

Threaten with the BBB if you have to, but get in touch with someone who knows how diagnose an a/c unit. You would be doing both techs a service by ratting on them.

Call them and tell them you want to know the following readings after they say your "system" is fully operational.

Condenser split
Condenser subcooling
Head pressure
Suction pressure
Evaporator superheat
Total superheat.

If the tech "doesen't know" what any of those are or tries to tell you they're not important, they fail at being an A/C tech.

'I asked him what was going on and he said the the return pressure to my outside unit was really high and he didn't know what would cause that.'
High suction pressure is usually an indication of weak valves. If that A/C technician doesn't know this then he's a dope! The first thing to do when you suspect something like an inefficient compressor is to pump the system down. If the compressor can't pump down, end of service call. It's compressor replacememnt time.

It could also be a result of a blatent overcharge. If you really really overcharge a fixed orifice or cap. tube system you'll have high pressure on both sides and will not have good cooling because of the high suction pressure and high evap. temperature. Get a different service company, the guy you have now is an idiot.

Blacknumberj1 is right but a new issue is brought up. Removing refrigerant, from a costumer viewpoint, means less cooling and the costumer will side with the serviceman that adds refrigerant, even if the real problem is size of unit etc. I've seen people fired over this issue, not that there are not bad servicemen. When you find one that gives you results ask for that person every time you need service and let him do his job

But the point is a system is designed to operate with a certian amount of refrigerant in it and overcharging it will make it not operate correctly. This may need to be explained to a consumer similar to having ice overflowing out of a cooler won't cool their drinks any better.

Proper refrigerant charge is critical. Too much or too little has an adverse impact. What has been previously suggested are some of the things that can be wrong. This could be a very simple problem also. If the filter is dirty, the A-coil clogged with dirt or, anything that prevents proper air flow THROUGH the coil, can cause high suction pressure.
Once you've established you have sufficient airflow through the coils, you can move to the next stage of diagnosis.
If the unit has been over charged or, run too long undercharged, excess oil could have entered the lines. This can reduce the inside diameter of the tubing, inhibit the transfer of heat, destroy or weaken the compressor valves (as Brandx has mentioned), clog the metering device.
Keith is right, many customers feel more refrigerant means more cooling and it's hard to convince them otherwise. I can't tell you how many residential customers call and say "I need you to come and add Freon to my air conditioner". As Blacknumber1 says, the correct charge is critical or it "ain't" gonna cool properly.

maryland irisman, I've seen your posts before and you strike me as a knowlwdgeable person in this trade. Thats why I'm totally surprised you are saying here lack of airflow across a coil will create a high suction. Nooo waaay in hell!! Just the opposite, your suction is gonna drop. And oil logging will not decrease the inside diameter of the refrigerant lines. You surprise me this time.

I had always understood that suction pressure was vapor pressure created by boiling refrigerant as it absorbed heat. If there is reduced airflow across the evaporator, both suction pressure and evaporator superheat will be low. Obtaining evaporator and total superheat is critical to diagnosing an A/C problem.

When an evaporator is oil-logged, the excess oil will form a puddle on the bottom of the line, creating a Venturi effect where the refrigerant will increase in velocity and carry the excess oil back to the compressor crankcase.

Please forgive my haste in answering and not trying to be too wordy. You're correct, under normal conditions, if there is no air flow through the evaporator, it will begin to ice up. I guess my focus is on the impression the unit may be overcharged. Once the works are hosed up, I didn't think it would do much good to discuss the proper operations of the unit. I am in favor of the pump-down method mentioned however, not all residential units have the valves to allow you to do that. If enough air is not moving through the coil, there will be a drop in the pressure and there will be a tendency to overcharge. This will inhibit the diagnosis for this particular unit...i.e overcharged or undercharged.
As you know, as you add refrigerant to a system it reaches a peak cooling plateu when properly charged. As more refrigerant is added, cooling starts to drop (temperature rise) since saturation and evaporation appear later in the coil and the temperature rises. Liquid refrigerant can begin to enter the compressor and migrate into the oil and can also begin to enter the suction side of the compressor. If the compressor attempts to compress the liquid (which it can't) the breaker will trip or, the compressor will go out on overload due to excessive amperage draw...if you're lucky, before it does much damage to the compressor or valves. The rising oil (from overcharge) or splashing (due to undercharge) can enter the intake also, creating the same conditions as liquid refrigerant. Perhaps one can be lucky and the condition that is caused by this situation is less damaging (to some extent) but will cause the evap. pressures to rise...a reed valve not completely closing due to liquid caught between it and the seat. If the reed valves are not damaged, they are weakened.
Yes, the oil does eventually return to the compressor. However, in this case (grossly overcharged), if it is continually being pumped through the system, it reduces the inside diameter of the tubing and, at the same time inhibits the tranfer of heat and there is still the chance of liquid refrigerant or oil entering the compressor.
At this point, to assure a proper diagnosis, this particular unit must be done by the book. I'm not an extremist so, I don't want to say this unit needs a new compressor (although it very well may). I also don't want to say it is exteremly overcharged. Before I would condemn it, I would make sure BOTH coils are cleaned. I would connect my ammeter to the common on the compressor. I would connect my high and low side guages. I would connect thermometers to the high and low side lines. I would measure the ambient temperature. Using the manufacturers chart for that unit, I would determine what the pressures should be. (so far, we're talking 5 minutes work unless coils, filters or fans need cleaning). I'd then start my diagnosis from there as to whether the unit is over charged, under charged or need replacing.
Anyone who cares to know how I would further diagnose the unit, please feel free to send me an email.

I don't understand why, when you get a "poor cooling call" the tech doesn't first find out what the actual cooling performance is, by getting cfm readings and input and output WB temps at the evaporator, instead of fooling with the charge first; very often there is nothing wrong with the unit, only too much load to cool. Also, it peeves me to think that the first thing they do is clean the condenser and the evaporator coils when they are not the problem. Even getting pressure and superheat and subcooling readings
alone are insufficient grounds to increase the charge. Isn't it simple to find out whether the condenser (and evaporator) is transferring the proper heat before doing an unnecessay cleaning and adjustment of charge.

All trouble shooting procedures must be performed in the proper order. If the suction pressure & also the head presuure are both too high it is an indication that the system is either overcharged or has too high a heatload being absorbed by the indoor evporator coil. There are "exceptions to my preceeding statement" as outlined in another of my web pages - Air Conditioning Excessive Airflow (& Heatload) - Excessive Charge -(now with a very low heatload.)

The first two checks are the outdoor air discharge temperature split through the condenser & check for hot air from the attic or elsewhere entering the return air. When the return chamber is under the furnace airhandler the air can be coming down behind the sheetrock into the chamber from the attic; that chamber must always be properly sealed & insulated if necessary.

Also, check for a very high humidity/latent heatload going through the cooling coil.

An authentic tech will not add refrigerant or remove it without verifying that the airflow CFM & correct heatload is passing through a clean evaporator coil.

The tech will also check the Super Heat & Subcooling temperatures. Also have a web page covering those procedures.

udarrell _ 2007

Here is a link that might be useful: udarrell.com