Tech Tips :

944 Heater Problems

    The first thing to look at is the heater valve.  16 Valve: It is located near the oil filter at the end of a metal pipe running along the cylinder head.  8 Valve: Centered between the head and firewall.  Start the car and watch for the lever on the valve to move to the closed position.  This should be done with the heat turned OFF at the control panel.  If the lever moves, then you need a heater valve.  The o-ring inside the valve is not sealing.  However, if the lever does not move, the problem is likely a vacuum leak.

    There are three common locations for leaks on these cars.  First, check the hose connection at the vacuum reservoir (the black canister next to the battery.)  If that line is connected properly, then move to the firewall.  There are two rubber elbows on the firewall were the hoses pass through.  Often an oil leak will soften these elbows causing them to become loose, lose their seal and create a vacuum leak.

    The next most likely cause is the control panel.  These panels are usually replaced as opposed to repaired.  Or the electric vacuum switch behind the glove box could possibly be the problem, but this is not typical.  

    Another possibility is that you are not getting full heat, and rather a warm blend of air.  Look under the dash on the driver's side.  Next to the console is an electric servo with a metal link that connects with a plastic clip.  These clips often break.  Simply replace this clip to allow the fresh air door to modulate again.