1976 Tbird blows hot air with the AC on

[Spit6]

My friend just got a 76 Thunderbird with only 15k miles on it, and it has only one problem, air conditioning.
My friend has been begging me to help him fix the air conditioning since it's starting to get hot outside. After looking at it last night, it looks like the AC might be working, but the heat doesn't turn off. He sets the controls to 65 degrees, the compressor turns on, but it blows hot air, and the temperature stays the same when changing from AC to heat.
Is there some kind of switch for the heater core that controls the coolant flow through it, and is there an easy way to test it?

[mcm51]

Congrats to your friend on that '76, those are getting harder to find everyday that alone one with 15k on it.......I'm only gonna give my thoughts on this issue because your not getting a lot of reply's, I can't tell ya how to flat out fix it but here are some things to consider, "assuming" that the ac is working correctly, it would'nt hurt to get a gauge on that low-pressure side to be sure, if that's correct and we do know compressor is coming on, the next thing I'd do is get my head under that pass.-side dash while moving the climate control selector around and see if any lever's are moving at all, also listen to hear if any vacuum leaks are going on under there that would keep say the heater blend door from moving properly, the only other thing I could think of is, I don't know what they call them, maybe an actuator, but they are silver or alumium in color, there may be one or two under there all close to or near the heater core box, this round canister may even be located under the hood just in front of the passenger firewall, regardless of location, there should not be more than two of them, these canisters act as a modern-day blend door actuator, in my life, I've seen very few leaking vacuum but more just stop functioning properly and just need swapped out, they use to cost about $30.-40 bucks.........
I hate to be long-winded, but in short, make sure ac works, via, dripping on the ground, water droplets on the coolent lines under the hood AND probably most of all watch and listen what is going on around that heater box while moving the climate selector......
I have'nt worked on a '76 since I was a teenager, my father owned a '75, so I hope that maybe I gave ya some thoughts to think of, if this Bird was near me in the n. Fla. area, I'd sure be willing to give it a look....................

[Spit6]

I appreciate your response.
I know the AC is working because the car leaves a puddle of water under it when the AC is on. Next time me and my friend hang out, I'll see if anything is moving while he messes with the climate controls.

[mcm51]

ok great, we know ac is working proper, with pass. door wide open, lay on your left side were you can really get a good look all around that heater box and yes, have your friend move first the selector(heat,defrost, mix, that one) slowly from position to position stopping in each one for about 5 seconds before moving selector to the next selection, I know there's about 6 of them, once he gets all the way to the last selection on the right, go ahead and go back to off on that one, all the while he was doing this, you should have heard or saw movement around that heater box, this test will of coarse have to be done with engine running to provide the vacuum we need, now while you are down there you can always slip that cable off the blend door arm sticking out and move it with your hand just to make sure it's moving freely inside the heater box, lastly, with your head still down at the box, have your friend slowly move that temp. selector all the way to the right and then slowly all the way back to the left, just once should do it for you to see or hear something down there on that one...
Sorry I can't be of better help, I've not been around a mid-70's heater box since the mid-80's so I'm going by total memory here, all in all, my guess on your issue is that your dealing with a blend not working correctly and that can be caused by either a broken cable from either of the slide selectors or your dealing with a non-functioning vacuum canister,(round, silver in color), OR my last guess would be a faulty climate control unit/box, one of the three is all I can think of...........