could have a holr in it did you ever check and see if the heater control valve is working by the blower motor looks like this

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Start your engine and turn the heater on. if the heater valve dosent suck in the one moving part on it, check the vacume line to the bottle for a hole or leek. if you have no leek then replace the heater valve. My vacume bottle had a pea size hole in it that I patched with duckt tape. if you replace the heater valve then make sure that the hoses are in the right place.
and if you just want to get it to work, you can zip tie the little arm on the heater valve so your heat is on all the time.

What?

this will get sucked in when you turn your heater on. If not, try to find a leek in the vacume line or the vacume bottle. that is the heater valve and it cost about 12 bucks. you can zip tie this part to get the heater to work if you have a vacume leek.