hi, my a/c is blowing cold air again.(2 months ago i had it inspected and they said all is fine but it needed r134a) any way yesterday i went to turn on the a/c and it was blowing warm air. and then i noticed that sometimes the clutch would engage and other times it wouldn't and then also i noticed that the line going into the cabin from the firewall was warm not cold like my haynes book says it would be. i bought some r134a with uv dye and tomorrow i plan on putting it in. but i am wondering if low r134a would cause the clutch to only sometimes engage and also i get a weird noise coming from the ac vents like gas is expanding type noise. what would cause that? any help would be apprenticed thank you. and also i did think about the thermo amplifier sensor being the cause but i figured that couldnt cause the weird noises and the clutch to not always engaging.