Why is my car’s heater barely heating at all & when it does work, it heats only intermittently?

My car’s heater is not working right. I get an occasional blast of warm air but then back to cold.
History:
In the summer, I noticed water coming out of the bottom of the car. I was told this was condensation and not to worry about it. It looked like a lot to me though. I noticed that sometimes my A/C didn’t work that well one day too. But I’d been on a five hour drive so I thought that had something to do with it.
More recently, I noticed water leaking when I wasn’t using the A/C. The heater was working fine and I’ve had it in for servicing and inspection.
Now the heater is not working. It blows cold air. Every now and then some warm air comes through but it fades back to cold. The longer I drive, it seems the more likely I am to get warm air.
Any ideas what this means? I bought the car this year and have already replaced a seat belt and the 02 sensor.
I am really hoping this isn’t going to be a huge cost.
Thank you.


Answer:

Firstly, the water that normally drips from an A/C unit during summer usage should always be clear. It drips a larger amount of clear water on more warm and more humid days.
That water is what condenses during the cooling of the warm, humid summer air.
Secondly, as for the heater, there are a few potential problems that can be relatively inexpensive to repair.
The heater may be blowing cold air with brief & intermittent warm periods if:

1.)  Engine Thermostat:  The engine’s thermostat is malfunctioning. If the engine’s thermostat is staying open too long, that is, not closing enough, it can prevent the engine from reaching its proper running temperature. In this case, the heater does not receive enough hot water to heat the outside air that blows through the heater.

2.)  Heater Thermostat:  The heater’s thermostatic controller is not opening wide enough to allow the hot engine water to circulate through the heater itself. The result is that not enough hot water flows through the heater to consistently heat outside air.

3.)  Low coolant level:  After the engine has cooled to the day’s air temperature, cautiously check your radiator to make sure it is filled to the correct level. If it is low on coolant, the flow through the heater can be reduced to an inadequate level. This could prevent the heater from reaching a warm enough temperature to heat outside air.

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