Bad thermostat or vent problem?

My car is a 1998 Hyundai Accent GL with approx. 175,000KM
I just got a new head unit installed by a place in town that does that kinda stuff and when I got the car back, the heater was not working. The climate controls are the older type sliders that go from left to right and I have it all the way in the red but all I get is cold air. I know that when he installed the unit, he pulled out the middle part of the dash (where all the climate controls are) and pretty much everything came out with it. Now the car audio place claims that all the vents are opening and closing like they sould and that my thermostat needs to be replaced. Well when I turn the car on the tempature gauge rises about 1/2 way in like 10 min (normal for eastern Canada at this time of year). Also, my thermostat housing unit and the pipe that comes out of it and goes into the top of the radiator is hot, however the pipe that comes out from under the radiator stays cold. And the two pipes that come out from behind the motor in through the firewall are hot.

So does this sound like a faulty thermostat or like he screwed up my vents? Is there anything else I can check for that would reinforce my argument with him?

I’m almost positive that the temperature select knob is connected to a cable and that cable runs back and connects to a flap that opens and closes, check the cable to see if it is connected still or take it back to them and have them check, since they caused all the problem in the first place.

Than you for the reply. I acctulay tore the thig appart today and it turns out he forgot to attatch the pulley to the latch that opens up the valve for the hot/cold air intake. I'll certainly make a BIG fuss with this guy. I'm also filing a complaint with the Better Business Bureau.