Heater/AC only blowing out of defroster vents

You may want to check the two water houses that feed the heater core. they both have to be hot. (they are usually located next to the thermostat housing.) If they are cold first check the coolant level. Fill up if needed, then you may have to check of there is an obstruction by the housing or the heater core is clogged up. I would first disconnect the hoses and see inside the thermostat housing with a lamp. Also blow some Air inside the heater core to see if flushing is needed. Well if those hoses are both hot then that must be a problem inside the cabin with the vents selection. Either an electric switch or cable. But there are already a few things to check first.

make him do it again... ?

I would return the vehicle to where the work was done. It sounds like something such as the blend door was not reinstalled properly, or something wasn't reconnected properly.

1st. make sure it is full of antifreeze/water. The defrost will be colder because the A/C comes on when defrost is turned on. The next thing is you may have a heater valve not opening as it should. Vacum or elect. heater valves have to open so hot water can flow for heat thru the heater core........hope this helps..

you may have abad slector door acuator.which is alittle motor bolted on the heater box.It move a door in box to direct air flow to right location.hope this helps.

Sounds like the blend door that diverts air flow inside the heater box is not working, or, the heater control valve on the heater hoses in the engine bay is not closing.

Maybe your dashboard vents are clogged, obstructed or stuck in close position somehow.

If not, check the air hoses that carry the cooled air to the main vents are not clogged, bent, ripped or simply detached.
If its practical for you, check if they are correctly placed, clean and general conditions are ok if you can.

If above are not the issue, go to check outlets of the A/C unit, its filters for the possible reason.

There is a flap that directs the air. the flap is controlled by a vacuum actuator. This is located inside the venting. The actuator is connected to little vacuum hoses that attach to the temperature control switch. Either the flap is stuck, or the actuator has gone bad.

Check the control cable that operates the diverter door in the heater box at both ends, to make sure that it operates the door when you move the control lever.

is it blowing threw the defroster if it is open the hood look on the left hand side of the fire wall there is a vacuum line there if it is broke blower will only come through defrosters if you have a vac canister it looks like a ball make sure the vacuum lines are good on it