Can any one suggest to resolve this problem?

1. frequent losing suction by pumps- partly due to common suction strainer choking in the sump, partly due to pump discharge check valve passing & air ingress from stand by pump.

2. pump discharge flow switch failure- the acting of flow switch cause stand by pump start

while facing this problem we are doing backwash from sump drain to clear strainer debris & increasing the sump level to 75% by forcing solenoid valves.

 

Strainer choking in the sump: Your water should not be dirty enough to clog that strainer except possibly after a ton of usage. Even then, if you live in an area where the unit has to be de-commissioned every winter it should be getting a thorough cleaning during spring commissioning. The evap cooler unit is behind the air filters so it shouldn't be getting clogged up with stuff coming from the air. I don't know where you get your water but it wouldn't be a bad idea to make sure your source is clean. Lastly, if you water supply is clean (which it should be) and your air supply is clean then I would look at the evap cooler media to see if it is shedding crumbling. There are companies that can test quality and specifications on that media for you. Donaldson is the only one that comes to mind but I know there are others.

Check valve: replace valve.
Flow switch: calibrate, repair or replace the switch.