I recently had a service call for no cooling on a 10ton rooftop. York. About 10 years old. It has two stages of cooling. I found that the first staged appeared to be low on R22. 15psi, suction, 100psi head. 50+ sh. The suction line temp was 77F. I continued to add 4lbs of R22 which brought my pressures up to 70s and 275h on a 75 degree day. the suction temp was 73 which makes a 33F superheat. Also forgot to mention this is a cap tube system.The second stage was running about the same pressures , 70s and 250h. but it had a 50 degree suction making a 10 degree superheat. The two stages are the same except first stage has a little more refrigerant. I have had this happen once or twice before where the suction line temp really doesnt change. On one of the systems i changed the liquid line dryer right before the txv. That brought the Suction temp down and the superheat down. The other didnt have a dryer. This system does have a liquid line dryer right before the cap tube. I just wondering if im in the right neigborhood again or if theres something im not seeing. Im affraid to add any more refrigerant already at 275 head on a 75 dgree day and the space temp is only 76 degrees.not much of a load.Any input would be great.