In normal use depending on the refrigerant the compressor was designed for, simply keeping the pressures in normal operating ranges will go a long way. The sudden BRRRR is often the starting relay turning back on. It uses the run current to know when to turn off when the compressor comes up to speed.
If the compressor was an R134a type, set the air compressor pressure regulator to about 35 PSI and don't pump over 450 PSI. Too high an inlet pressure with a high discharge pressure will overload and stall the compressor. This can lead to the motor overheating and burning out. Pressure well above 450 PSI on the outlet can lead to valve failure or a blown head gasket.
If the compressor is an R22 model, it will have a lower displacement (pumps slower) but will be able to take a little higher pressure on the inlet and outlet. You really need to limit the inlet pressure on the R134a models as they were designed for lower inlet pressures. High pressure will overload them and let out the magic smoke.
In simple terms of the volume of air, when you pump 1 atm (0 PSI) of air it will pump slowly and you can reach fairly high pressure without stalling the motor. When you double the inlet pressure to two atm (14.7 psi) you are asking the motor to haul twice the material up to a high pressure. This almost doubles the load on the motor. Increasing to 3 atm (29.4 psi) again increased the load on the motor and increases the pumping rate. If you feed it about that pressure for an R134a compressor and output about 150 PSI, your have the compressor in the normal operating range. When you shove 8 atm (7 bar or ~100PSI into the inlet and expect an outlet pressure above 300 PSI, you have it fatally overloaded. It will overheat and go up in smoke if it runs long that way. If you are lucky, it will stall, kick in the start, then trip out due to too high of current.
You may have burnt the insulation on the motor winding on the first try so the windings are stating to burn out. This may be the reason for the lower pressure on the second run.
It does help to know what you are doing when you play with a fridge compressor so you don't burn it up early in the life.
If you have an AC Wattmeter such as the Kill-a-Watt, you can monitor the power used by the compressor to tell when it is up to full load. Full load amps is marked on most compressors. When you exceed full power current, it will be overheating. This overload is what kills many AC compressors in a heat wave. The inlet pressure is high due to a hot room, and the outlet pressure is way too high due to the hot outdoor temperature. Sagging voltage from an electrical overload increases the compressor current and hastens the burnout.
Full load Amps is listed on the compressor nameplate as FLA. The maximum start current is marked as LRA which stands for Locked Rotor Amps.
Kill-a-Watt meter
But before i did that i poured in some synthetic motoroil (10W-40) and when i did come to about 500psi the compressor sounded wrrarrrr and then did shut down, i plugged out the hose and some oil dripped out (Only 1-2 drops). After 10 sec i plugged it in again and it worked again but this time only to about 300psi and the same sound again.
