96 Crown Vic Heater Control Problem

[Captain 203]

My heater blower only works on HIGH! WHEW!! and the vent control only comes out of the defrost area. If I turn the blower to any setting but high it stops. And no matter where i set the location control (vent, mix,etc) it still only comes out of the defrost areas. Where do I start?

[ModMech]

You have two seperate problems.

1) Blower speed, the fix for this is either the resistor block, or the switch. Unless you are skilled in electrical troubleshooting, there is no real way to tell which is the problem. So, for about $10, replace the resistor block (they are the most common cause anyway). It is located under the hood, RH side near the large aluminum colored A/C accumulator (has 4 wires attached to it, and fits into the air handeling box).

2) The loss of mode control is most likely due to either a bad selector (30% chance) or a leak in the vacuum supply sustem (70% chance). The vacuum supply comes from the engine via a GREEN (as I recall) small diameter plastic tube that run behind the engine and thru the firewall somewhere near the throttle pedal. These often become disconnected. One way to find were it is unplugged (or leaking vacuum) is to run the engine and listen for a slight hissing noise, follow it to the vacuum leak. Aside from that, find the rubber hose/plastic tube that runs from the LH footwell area under the dash to the HVAC control head, and repair any leaks you find as you go.