If you are getting heat all the time, check the function of the vacuum controlled flow valve on the fire wall behind the charcoal canister. Turn on the heat on by setting it to 85 deg if the engine is cold and then pull off the vacuum hose. There should be vacuum at the hose with your finger and the valve should spring closed when the hose is pulled off. Make sure thst some one has not simply removed it and bypassed the control valve.
When they fail the usually fail in the closed position. The electromagnetic solenoid sticks internally and you have no heat.
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