Why would your AC work but throw out cold air only in the top vents not through the front vents?

Usually it's because of a vacuum leak from a defective hose or a vacuum hose that is disconnected. Sometimes, if it has a vacuum canister, the canister is bad or the vaccum hose has fallen off or somebody forgot to reconnect the hose. Usually it is a very small hose that you will need to find, like 1/8 inch. This is caused by the vacuum from the engine intake manifold not getting into the cab. Check that vacuum line for soft spots, kinks or being disconnected. Good luckJoe The vacuum is used to activate vacuum motors which open and close doors in the air ducts. The doors control the flow of the air to the correct vents. For instance, warm air is sent to the vents below the windshield to provide a defrost function. Cold air is often sent to the vents on the front of the dash for air conditioning. After a period of time, the diaphragms in the vaccum motors will begin to leak causing the vacuum motor not to work. This is a common problem on 1980's Mercedes and can only be remedied by replacing the vaccum motor.

But, first check for loose or leaking hoses and fittings or a defective vaccum switch.

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