Checking the power source Power supply fan is noisy or having interference Power supply light does not turn on or power supply fan does not spin Testing the power supply separately from the system Power supply light is on and flashes Ordering a replacement power supply This document pertains to HP and Compaq desktop computers. Figure : Power supply light If the small light on the power supply does not turn on and the fan in the power supply does not spin, and it looks like there is no power, see Power supply light does not turn on. If the small light on the power supply turns on, see Power supply light on or flashes. Computer Does Not Start (Windows 10, 8) Windows 7 Does Not Start Computer Does Not Start (Windows Vista) Resolving Startup Problems (Windows XP, Me, and 98) Checking the power source Figure : Power supply vent If you have tried all of the previous steps and the power supply light remains off, use the steps in the next section, Power supply light comes on or flashes, to reseat the cables and check the power switch connector.

If the power supply fan spins when the computer is turned on but the light does not turn on, see Power supply light comes on or flashes.lg window ac service manual Figure : Commercial PSUsbest ac units 2014 Figure : Consumer PSUsair handling unit package Figure : Example of common power connections If the LED is on solid If the LED is still flashing If the LED light is now off Figure : Find the Spare Number or Part Number If the part number is not listed on the power supply or is unreadable, follow these steps to use the HP PartSurfer website to find a list of power supplies that are compatible with your computer. If you use a power supply that is not listed on HP PartSurfer for that computer as a replacement, you risk voiding the computer’s warranty or damaging the computer.

Open the HP Parts Ordering website (in English). If necessary, select your country/region and language in the upper right corner of the page. Figure : Example of a power supply part listed on the HP Parts Ordering websiteWritten Written Written Why do we need cooling?The body core temperature is around 37°C and that of skin is 33.7°C but the body constantly converts chemical energy to heat. Hence to maintain this temperature we need to dump that heat in surrounding environment. Mechanism of heat rejection :Radiation : Q = constant * {(body temp in K)^4 - (surrounding temp in K)^4}Convection Q = h * Area of body *{(body temp) - (surrounding temp)}Evaporation Q = he * Area of body *{(body vapour pressure) - (surrounding vapour pressure)}   Out of which convection and evaporation play major role as temperature difference between the body and the surrounding is very small to carry out significant radiative heat transfer.  Convective heat transfer on the other hand plays important role.

It actually moves heated air from your skin and replaces it with cool surrounding air. In natural convection this happens due to density difference between hot air and cold air.    Evaporative heat transfer takes place as water from the body evaporates through pores in skin and takes away the heat of evaporation. The driving force for this mechanism is vapour pressure of water in surrounding air. Why air circulation is important?Convective heat transfer coefficient "h" in the equation depends on the velocity of air. Roughly it is related to velocity V as h=8*V^0.6. Evaporative mass transfer coefficient also varies roughly the same. Hence by increasing velocity of air around the body, we can dump more heat. This reduces the temperature difference required for heat transfer. Logically one can increase the set point of AC to higher temperature (27-28°C instead of 24-25°C) and still have same level of comfort. This will help AC to run the compressor for less amount of time.About the heat rejection from fan Fan motors are much more efficient compared to compressor.