Good Mr. Claudio, I also note that if a Tandem type compressor is damaged, it must also be replaced by another Tandem type compressor of the same capacity. As you have noticed when you see those 2 compressors, they are joined together by a thick copper pipe (equalizer) and the function of that pipe is to keep the oil level between both compressors at the time of turning on and off. oil is usually migrated or the most critical point is when the compressors are turned off, since the oil migrates from one compressor to another if that pipe (equalizer) were eliminated or you would put 2 compressors without that pipe, the compressors would eventually be damaged since one of them would run out of enough oil for lubrication. When installing 2 compressors in Tandem, you should always install the oil equalizer tube and that is why there are Tandem type compressors, since a normal compressor cannot install that pipe. a Tandem compressor and a normal compressor cannot be installed in a circuit with compressors in parallel due to the oil problem. In the Tandem systems that I check, those of 10 Ton, they use 2 compressors of 5 Ton each connected in Tandem and when turning on the # 1 compressor after 15 seconds it turns on the # 2, the low pressure is at 75 lbs and turning on # 2 the pressure drops to 65 lbs. In other Digital systems that use 4 compressors, 2 in Tandem per circuit, there is a single compressor and then according to the cold requirement of the premises, the remaining others are switched on. This type of Tandem system has more disadvantages than advantages ... since damage to one of the compressors will contaminate the other compressor and could also be damaged, that is among other things. One of the advantages is that if you have a 10 Ton system of a single compressor, that compressor would always be working at full load and moving just that whole amount of gas (by weight) and the compressor would get hotter and work harder, instead with the compressors in Tandem, they share the load and the work. in theory it is said that the compressors in Tandem have greater cooling efficiency.