'86 Ford Crown Vic heater system

logeorge · 10-06-2011, 06:56 PM

Does anyone know where to get information on the heater controls for '86 Crown Vic and Merc. Grand Marquis? We have one of each, both with automatic climate control. On the Ford it won't heat. I've checked the heater core and it is not plugged up. When the control lever is moved to "floor" the vent door opens and the blower stops running. The A.C. on the Merc blows cold going downhill, but blows hot air on an upgrade. I can't find anyone around here who will even look at them. Maybe because the cars are older than some of the mechanics.

Skyhawk · 10-07-2011, 11:27 AM

Look in your owners manual for the climate control self diagnostic system procedures. If the problem is not electronic, that is the control module, then it is usually vacuum related. You could have a line vacuum leak or a vacuum motor with a leak. The vacuum motors commonly develop an internal leak due to a pin hole in the diaphram. Just some thoughts.

grog11 · 10-07-2011, 01:09 PM

I found some information on the 1986 control panel at autozone, believe it or not. Looks like you do have a vacuum switch behind the automatic climate controller in the dash as Skyhawk suggested. Hope this helps,at least its a start.
Here is a link to the repair info section.
| Repair Guides | Wiring Diagrams | Wiring Diagrams | AutoZone.com

logeorge · 10-08-2011, 10:05 AM

Skyhawk: Thanks for the input. Unfortunately, neither the owners manual nor my Haynes manual give any clue as to the vacuum hose routing or location of the vacuum diaphragms that open and close the doors in the plenum. I'll probably need to find a factory service manual. The more I think about it, the more I think someone has had it apart to replace the heater core and mis-routed a couple of the vacuum lines. Replacing the core on these is a real chore. I've done several years ago,but not on these two vehicles. You about have to be a contortionist to get at some of the under-dash stuff. Being about 50 years younger would be a big help, but I'll get it, given enough time.

logeorge · 10-08-2011, 10:14 AM

Grog11: Thanks. I'll check Auto Zone out. I found the vacuum switch. It seems to be working and I can't hear any leaks. As I said to Skyhawk, I think the hoses on the Crown Vic have been mis-routed. I'll check the Merc for leakage at the vacuum reserve tank or hoses going to it as a first step and go from there.

Pletchaj · 10-08-2011, 09:14 PM

climate control issue vacum had a lincoln do a similar problem the up hill down hill ... fill the radiator, its low or has an air bubble so when you change grades water dosent feed into the system ... find the bubble

logeorge · 03-09-2012, 07:17 AM

I took out the heater plenum to replace the heater core. Unfortunately, neither the Haynes or Chilton manuals mention the fact that there is a second nut on the stud that attaches the plenun to the firewall. This is the stud that passes through the A.C. evaporator housing at the top corner, on the engine side of the firewall. It is mounted in the heater plenum and passes through the firewall and the evaporator housing. There is a second nut between the housing and the firewall. I presume it was put there to hold the plenum in place until the AC parts were installed. You can't see it and can't get the plenum out until it is removed. You can take off the evaporator housing(a lot of work) or open the hole up until a socket can pass through and onto the nut. That is is what I did, and later made a plate to cover the hole so the outer nut would have a bearing surface. Just a strip 1/4 " aluminum with a clearance hole for the stud. Opened the hole around the stud with a rotary file in a die grinder. Once the plenum is out, you will see there are four "doors" inside it, operated by vacuum motors. The ones on either end are mounted on rods and will probably be OK. The others are hinged by having a thin area which allows them to bend to open and close. These are probably broken. Mine were. I rehinged them by attaching a strlip of piano hinge, using spacers to get the pivot point where it was originally, 1/4" for one and 3/8" for the other. I drilled out the rivets holding the plenum halves together and used #10 screws to replace them. It seems to work OK, but I haven't been able to test it since reassembly. You don't have to take the dash clear out to remove the plenum, but do have to take the bolts out that are behind the top of the kick panels. It helps to be a contortionist, too. I haven't thououghly tested it because now there is a conn. rod knocking. Yes, I know I'll have more in the car than it's worth. I'm going to drive it, not sell it. Cars don't rust out here! Hope this helps someone! L. O. G.

Poppy · 03-09-2012, 08:10 AM

LOG,
Thanks for posting that bit of info.
Too often it seems that the manuals take you as far as you could get without them, and then leave out the little details that are needed to finish the job.
At any rate, I'm glad that you figured a way to make it work.

I recall once not being able to get a heater core out of one of my cars, and I ended up cutting out a portion of the heater box, and later repairing it with caulk, or duct tape, primarily because I couldn't get one or more of the screws, or bolts out.