99 Jeep Grand Cherokee, Musty Odor When Heat Is On?

When I Turn On The Heat, I Get A Musty, Dirty Odor From The System. When I Turn On The A/c It Last For A Short Period But Then Clears Up ? Has Anyone Experienced This Problem?

When I Turn On The Heat, I Get A Musty, Dirty Odor From The System. When I Turn On The A/c It Last For A Short Period But Then Clears Up ? Has Anyone Experienced This Problem?
I had the exact same issue with my 98' Grand-Limited. About the only thing you can do is keep your air filter clean. Get a K&N filter if you dont have one already.

comes from water not draining properly from the ac condenser, there is a drain hose on the fire wall or under you could blow air through it, also you can buy spray can, not sure where, to spray into the air inlet, it should take care of the mould in there.

jeepmad, what exactly is cleaning your engine air filter or getting a K&N going to do for the air coming into the cabin? No, your engine air filter is not connected to your cabin air system. the odor is from bacteria mold and mildew in your HVAC ducts or on your evaporator core. you can reduce this problem by installing a cabin air filtration kit.
Part name: "Cabin Air Kit" Part number: 82208300 List price: $49.00
To get rid of the odor that is already there, I have used a product called "Pure Air" from interdynamics it's a pump spray and it is just a sanitizer to kill any bacteria in your air duct system. i got it for like $5 at a local auto parts store. all you do is spray it into the air intake below the windshield on the passenger side of the car, and with the recirculate turned on spray a mist into the passanger foot well.

Any spray sanitizer will work, I have been using Lysol for years, works great