We just bought a 2008 Honda Accord about a month ago. We noticed that when the ac is on, the car has a loud humming noise. Once you turn off the ac the sound stops. Last week, our ac started blowing hot air. We bought a DIY ac recharger but it wouldn't in take any of the product, the vavle stayed on the red area.
My car has 137000 miles.
My car has an automatic transmission.
To determine the exact fault, the system will have to be tested. You can obtain that service by requesting an a/c system diagnostic. If the a/c switch was set to "on" and you attached a can of refrigerant with an integral color-coded gauge, the reason the gauge displayed in the red (overcharged) zone is the compressor was not on (that’s an indication of the fault by the way; for some as yet undetermined reason your compressor is not coming on). What happens when the compressor is NOT on, is the LOW side pressure is actually way, way above that expected during normal re-charging. So, when you attach that gauge to a non functioning system the gauge necessarily reports the pressure as "off-scale" high (red). A functioning system has a LOW side pressure of roughly 35 PSI (high side could be in the neighborhood of 200 PSI) while, again, when the system is off, or not functional, low side pressure rises to a static value of roughly 70 PSI.
At any rate, the experience you are reporting with the recharge can suggests your compressor is not turning on. The noise you are reporting could be caused by faults in a lot of different a/c related components: the condenser fan, the passenger compartment blower, the compressor clutch, or the compressor itself. Your system has at least a partial charge so what the mechanic will likely do initially is turn the compressor by hand (with the car OFF) to see if it is seized. If it is not seized, and yet when the A/C switch is in the on position, there is no power to the clutch, that circuit has to be diagnosed. On the other hand, if there is power to the clutch, but no clutch operation (the a/c clutch mates the compressor itself to the drive pulley), then you need a new clutch. There are other checks that will be performed, if necessary, but the bottom line is if you request the diagnostic, the mechanic will pinpoint the fault for you and get this resolved. It is probably a reasonably circumscribed fault. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.