My brother-in-law has a 87 camaro and the heat doesn't work. It has a new thermostat, both top and bottom hoses are same temperature after the car warms up, doesn't seem to be a problem with the heater core. I noticed the other day that when he moves the tempertature control from 'cold' to 'heat' there is a cable under the dash on the passenger side that moves. It looks like it shoulc be connected to something but I can't tell what. Any ideas?

There is a door under the dash and that cable should hook up to it. It's a door just like the door on a icecube machine on a refrigerator so just reach under there and pull it down you should feel heat connect the cable to it also

There are basically two ways that temperature control works. The cable controls a valve on the heater core or a damper. This must use a damper.

Vacuum usually controls the mode of the system or where the air gets discharged.

First is the cable flexing or acutally moving?

If it is moving along the length it is not secured. Which might be just simply slid the cable housing into a slot or tighten a little bolt and clamp the cable down again.

If it is secured cable just flexing then undo and try moving the handle or attachment point of cable end. If you get heat then adjust the cable to full heat on dashboard and full heat on damper and tighten cable hold downs or cable end depending on the specific system you have.

If no adjustment is possible at either end of cable then buy a new cable.

Ps: you can always try a penatring oil on the cable might be just lightly seized and not moving fully

I think the heater core is shot. Tell him/ner to lift the carpet on the passenger side and see if it's wet there. Do the widows fog? If so, have heater core replaced.

The windows don't fog and he has checked to see if the carpet is wet. No sign that the heater core is bad. Could the heater core just be 'clogged'?

If both hoses from heater core are the same temp hot then the core is good.

If the cable is not hooked up then it will not move the heater control flow valve.

Check to see if any of the damper doors or vavles move.

If they not moving they are not working.

I did work on older truck with same prob not heat. I removed both heat core hoses from eng and water pump and ran water from garden hose backwards through the system.

I have run into plastic bags plugging up the hose as someone let it get into the rad core... Don't ask me how... I just fix it.

Good luck

This is a common problem. Take it to a mechanic and have them "reverse flush" the cooling system.