2001 ford focus heater blows cold air intermittently

HEATER NOT BLOWING COLD,NO HOT AIR FROM HEATER,A/C BLOWS HOT AIR,A/C NOT BLOWING COLD, COLD AIR FROM HEATER,BLEND DOOR ACUTATOR CLOSED,HVAC UNIT NOT OPERATING,
http://alltypesofpartsreplacing.blogspot.com/2012/12/heater-not-blowing-coldno-hot-air-from.html

you need a ac charge or the heater control valve is bad also check the compressor

The heater core has gone out, it's located under the passenger side dashboard

Sounds like whoever did the repair work did not install the solenoid correctly or did not reassemble everything properly. If you had heat prior to the repair, the heater control panel must have been working. The mechanic must make a better diagnosis than this.

does your blower motor work or it just blowing cold air?
if it does not blow then check the fuse, the motor may be bad
if it blows cold air only then check your coolant level
check to see if the heater hoses are hot on both of them
if the hoses are hot then you may have a blend door actuator bad

if all else fails, change thermostat, and bleed are from system if needbe.

could be your heater core controls your heat

check your coolant- if it is low, top it off. you could have an air bubble or the heater core could be clogged. if not the air mode door in the heater box might not be moving. that is the hardest and last to check

maybe the heater matrix could be at fault, thats the bit that controls the temperature in the car.

change the heater core