Blend Door Problem?

With my 98 Blazer (manual temp controls) I have very little heat when its cold out. The warmer the air temp the warmer my heat. I have heat both to and from my heater core and my blower fan works fine. Does this sound like an actuator problem to you? Like my blend door is stuck open part way?

Make sure the coolant level is correct in the radiator and reservoir. Engine operating temperature should be around 200 degrees. If both are ok, the blend door actuator could very well be your problem.

Usually its a clogged heater core and not the door. Check the vac lines under hood drivers side -the last one thats plastic goes to the heater controls. If bad vac default is defrost.
Then I would flush the core by removing the lines at firewall and I use 3' sections of 5/8 and 3/4 heater core and a garden hose to flush both ways till freely running. Cover distributor so it does not get wet and when removing the stock hose ends position them up so dex cool stays in! Reconnect and top off rad and res to Hot full when cold. Hope that does it.

That's a great procedure for flushing the heater core but when both heater hoses are warm, the core is probably not restricted. I agree that problems with the heater core are far more common than the blend door actuator however; heater output temperature is low and not consistent. That could indicate low coolant level causing an air pocket in the cooling system, intermittently starving the heater core of coolant. A faulty thermostat could cause low heat; the clue was "warm" heater hoses, not hot. The blend door actuator is a long shot, but it is possible. I don't believe we're dealing with a vacuum issue here; the blend door actuator is electric on '98.