There's a fuse under my hood that controls the heat, ac, defroster etc. a couple months ago they all stopped working. I checked the fuse and alas it was blown. I've bought replacement fuses with the same amperage (30) and when I start the car back up they start working for a bit and then blow within 5 minutes. What could be causing this? None of the other fuses in the box have this problem
The only fuse in the under hood box that may affect this is #19 (the Run Relay, Heating, Ventilation, Air Conditioning Blower).
If this is the one that keeps blowing, there is likely something wrong with the Blower Motor Control Module / Resistor or the motor itself.
Disconnect the blower motor and see if the fuse stays. If it does not blow, then the likely cause is the blower motor is starting to fail.
If it does blow with the motor disconnected, then it most likely the Blower Motor Control Module / Resistor causing the fuse to blow. This is a very common failure and replacements are readily available.
If both are disconnected and the fuse still blows, you have a short somewhere and will need to trace wires to find it.
You have to find the fault - this will mean isolating or disconnecting each device until it stops blowing and then dealing with the item that is at fault.
It could be all sorts of things (this is the fun part of electrics!!) a motor starting to seize, the A/c clutch failing / shorted, a wire chafed and shorting when one of the fan speeds is selected...
There are so many possibilities that a definitive answer is not possible but that is the process.