Q: When I turn on the heater I get heat but only lasts about 10 min. then it blows COLD air and heat won't work at all? Any ideas about what would cause this?
A: Dont waste time with the thermostat,if it is faulty you will have other engine problems too.On these models of Ford the air conditioning is supposed to run all the time,i.e. the air first gets cooled down to get rid of the moisture,then heated up. but max to 32 deg.C There is a bimetal sensor/vacuum regulator under the dashboard, passenger side, which regulates the door for the heater core, it compares the temp. inside with the temp outside and opens or closes the door automatically. gets a temp. reading for outside temp by means of a small black hose comming out of the air cond. assy, after the fan, but before the heater core, find it around the passenger legs inside the firewall, if unplugged you will feel cold air comming out of the hole from the fan, trace it and will find that temp regulating vac. valve, quite a difficult affair, but that is the only way, then from that valve comes a transparent about 1/2 size hose, connected to the vac.motor for the heater door,try disconecting it, that will keep the door closed all the time and the heat will be full blast. Try fiddling with that bimetal spring, when you find the whole vac. valve/regulator assy. to reduce its sensitivity and send less vacuum to the vac.door motor. The whole repair is time consuming, because all the stuff is under and inside the dashboard,I have not found any reliable info or diagram in the library, or Chiltons, or Haines manuals..The bimetal sensor looks like a thin metal coil spring inside the regulator, one side attached to a primary vac. valve with a small black and the big transparent vac. hoses, other side to a plastic black lever for manual temp. setting, it changes its length with the temp. change and opens or partially closes the connection between the small black vac.supply hose and the transparent bigger size one for the door motor. Good luck with the repair.