The most likely answer is that he disconnected a wire that he did not reconnect. You should take it back to the shop and let him reconnect it. He will know exactly where that wire is because he has done it many times.
I'm not a mechanic / technician but I was looking at fordparts.com and comparing the heater cores for the 1996 Ford Explorer and the 2000 Ford Explorer and they show the same part number ( so apparently the answer would be YES )
why is heater on 1995 explorer lukewarm
The air conditioner or heater continually runs.
the answer is air conditioner
BIOSPHERE
If your heater is a heat pump , then yes.
call a mechanic who couid repair it call a mechanic who couid repair it
It should be the same as my 1995 - at the firewall the heater hose nearest the drivers side is the inlet hose to the heater core
it could be the heater is leaking!
BIOSPHERE
Yes, a remote control is included with the LG 7000 / 3850 BTU Air Conditioner / Heater.
Take it to a mechanic.