vacum pump is located on pass. side innerfender. open the hood and turn the key to run and it will run for a few second's, just listen for it and you can find it. your problem could be related toi a bad pressure cycling switch, low refrigerant or a failing compressor. also, like was said before, make sure the condenser (in front of radiator) fin's are as straight as possible and clean. if it look's a little dirty, lowe's sells some cleaner for air conditioner's called coil cleaner, that will clean the dirt, dust and road grim out of it. here at home it's in the lawn and garden section. ask them for it.