Your Vestar AC cycles on and off based on the sensor in your home. This is what keeps it at a constant temperature and if the sensor is not working then your Vestar AC does not know when to turn on and off. Sensor location can also be a problem. If the sensor is in a small room and the door is closed, that room might reach the desired temperature causing the AC to cycle off leaving the larger rooms too warm. Your sensor is usually best placed in the largest room.
If your sensor is not working properly, it can cycle on and off, with little time between activation periods. The home can be too cool or too hot, even if you adjust the temperature setting at the control panel. If you allow the system to continue on this unusual cycle, critical components may break down.
Turn off the Vestar AC, and remove power from it completely by shutting off the breaker at the main electrical panel. Access the indoor air conditioning unit's evaporator coil. It may seem hidden with a cover on it for protection. The sensor should be extremely close to the coil. If it is touching the coil or bending away from it, you have found your sensor problem.
Carefully bend the sensor back into place. It needs to be close to the coil for an accurate temperature account. Any unusual angles toward or away from the coil causes the erratic air conditioning behavior as seen before. Turn the breaker back on and activate the air conditioning. It should work normally now.