2002 XLT V8, fix to vacuum heater valve
My 3rd-gen XLT had the heater control valve burst about 2 years ago, I replaced it but couldn't figure out why the new one wouldn't open/close when it should. I finally got around to it yesterday after reading this thread. I'm sure that for even more than 2 years my heater valve has been stuck open, so that the coolant is always circulating and even on max-ac the air is being heated and then cooled. Since I just had the AC compressor replaced (it was shot after 177k miles), I wanted to get this heater valve fixed.
Picture of dashboard apart, with red/yellow/blue/white vacuum control lines, and black supply line (from vacuum reserve):
Now, on my 02 XLT, the black supply line comes in thru the firewall, goes to the vacuum reserve, then joins the other multi-colored vacuum lines on the back of the mode-selector switch. However, on its way there there's a tee-off, and another run of black vacuum line goes off behind the air vents to parts unknown. That second black line is accompanied by the grey heater valve control line. See yellow-ish tee and grey line in this picture:
It seems as though the second black supply line and grey line go off to some sort of control-switch mounted behind the vents, and very hard to get to. I don't know what the design is supposed to be or do, but for years now it hasn't worked. So I came up with a work-around to tee off the white vacuum line (which has vacuum when Mode is Off or Max-AC, but no where else). I used a small (5/32nd) vacuum-line tee and 90deg elbows as shown here:
I first cut the second black vacuum line coming off the tee in the black supply line and sealed it off with a rubber cap. Then I cut the white line, and used the tee and 90deg elbows to join the grey heater valve line on to the white line as shown:
Then I put it all back together and tested it. see valve open:
and valve closed:
and yes, it seems to me that max-ac is colder now that the valve works. I don't know why Ford didn't do it this way, or how they intended the grey line to get vacuum, but I'm calling it done.