I have done a site search and no one seems to know for sure how the HVAC system on the big Merc and Crown Vic are controlled. One answer says it’s vacuum, another says it’s electrical, another says electronic via the BCM. Which is correct? Does it have an electric servo to move the flapper door(s) like the Taurus I’m familiar with? Even the BCM has to have something to tell to move the flapper doors.
In the car I’m looking at, the lines into and out of the evaporator are cold when A/C is selected and the compressor clicks in. That makes me think the issue is with air direction. All I have to do is figure out why.
The vent doors are probably powered by a vacuum source. On some of the fancier systems, the vacuum source motor can be switched by electric control. Do you see a vacuum hose headed from the intake manifold area of the engine and going in the direction of the HVAC doors through the firewall?
If the system is the automatic system the blend door is controlled thru the Electronic Automatic Temperature Control Module. If it’s the manual system the blend door is positioned electronically depending on where the temperature knob is set.
Blend door problems are common and a guy who spent some time examining the issue on his Lincoln determined it’s due to the stepper motor still tugging on the door no matter which stop the door is against.
On the EATC units it was recommended that to help things a bit that the min. 60 and max. 90 degree settings not be used and that the 65 and 85 settings be used instead.
The air out of the vents on A/C will be much colder than 65 anyway so that’s not an issue.
You can run a quick diagnostic test and if it has EATC may show a code for a blend door failure.
With the engine warm, push OFF and FLOOR at the same time and then quickly push AUTOMATIC.
The display will show gibberish for a while and then possibly show a code.
To clear the display push DEFROST.
EATC or non-EATC, I think the blend door operation is the same and the same failures occur. I’m not sure at all with this model of Mercury but I think that generally the blend door actuator can be accessed by removing the glove box. Changing it is a bit more difficult. That might allow you to get in there and make sure of the problem though and the heater path could be closed off manually as a temporary cure if the blend door is the problem.
It does appear to be the blend door actuator. Unfortunately fixing it requires removing the dash. It sits on top, directly under the dash pad. I’m not looking forward to this one.
Thankfully I’ve never had to go through that blend door fix with my Lincolns. I seem to remember vaguely from a Lincoln/Mercury site that the blend door may be accessible without totally removing the dash.
Maybe dropping the steering column, loosening the dash mounting fasteners, and sliding it back about 6 or 8 inches may provide enough wiggle room to change it?
The wonderful world of molded plastic…
On my 2005 Vic, sometimes the “temp” control knob will do nothing at all…Maddening when you want a little warm air defrost on a damp, rainy day…On this car, after it has been parked for an hour, the system works normally again…The guys on crownvicnet.net should be able to help…
