I just bought a 79 Lincoln towncar, the.

Hi, I just bought a 79 lincoln towncar, the heater seemed to work good right away, drove it about 70 miles, getting close to home, noticed the temp was not warm in the cabin any more, I replaced the thermostat, did not change any thing, I traced the cable for the temp setting to a canister under the dash, found a vacuum line to this canister, I moved the temp setting from hot to cold and back a few times, this canister moved an arm and the temp did respond a little but not much, I pulled the vacuum line off and the canister really responded and the temp went max hot, not sure where to go now. Thanks.