1990 Cadillac Brougham Heater

Check for control valve in heater core coolant lines. Check for operation. Also remove glove box and check air mix door for proper movement from hot to cold.

I was thinking the same thing and checked the heater control valve earlier. I noticed there is a fitting coming of the back for a vacuum line but there is no line to it. Looked around and couldn't find a hose anywhere that was off or looked like it went to it. Does it (control valve) have to have vacuum for it to work? How will I no if the valve is bad? It looks like the valve threads into the intake. Is that true and if so is it hard to take out?

It needs a vacuum line to operate it. Look around the area for broken line. If none try to manually open valve if you can. Check then for heat. If that works you can use a tie strap or piece of wire to keep it held open. If possible please submit a photo of valve.

The control valve seems to be incased so i don't believe it can be opened manually. Any ideas? How do i know if its bad. I assume that if the hoses dont get hot then it must be stuck closed. Is it hard to replace?

Most likely stuck closed. Can you submit a photo of it please. No image on it I can find.

Here is the pics. Got good vacuum going to it now but hoses still not getting hot

Should be attached by hose clamps. Usually just a 5/16" socket to undo clamp screw.

Replaced heater control valve. Old one was definitely stopped closed. Car heater would still not get hot until I pulled the vacuum line off to the valve. I had just run it(vacuum) to it the other night after u said it needed vacuum to work. I teed off an old line to run a new line to valve. The old one had no vacuum line run to it even though there's a vacuum fitting on it. I don't understand how it works but it seems like when I hook up the vacuum line I ran to the valve the vacuum must be pulling the valve closed. The heater hoses are definitely getting hot now with the vacuum hose off the new valve and the heater is working great. It quits blowing hot when I hook vacuum to the valve. This seems very strange and not sure it's normal. Took off the new vacuum tee and line I ran and just left no vacuum to the new valve. Everything is working great but my question is will it hurt anything or the valve by not having vacuum running to it?

Should be fine with no vacuum. Usually vacuum is supplied by the climate control/selector unit itself. You can just leave it off for now and when you need a/c just zip tie the valve closed. Valves come in 2 configurations; normally open and normally closed. You should be just fine with it in there and not hooked up. Just cap off the tee you put in place in the vacuum line so you don't have an engine vacuum leak.