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Moisture inside Honda Civic

Ever since I got my car back from having an oil change, new battery, and tire rotation, there has been moisture inside. This includes condensation and ice inside on my car front windshield and a scarf I left on the floor was soaking wet and partially frozen. The area above the passenger side visor appears wet (on the car ceiling). I promise the windows are NOT down!

Your AC evaporated drain is most likely clogged. The drain is usual on the passenger side firewall. The water in the pan is likely freezing, then when using heater or defroster is thawing out.

Do you have a sunroof?

There is also the possibility that the HVAC system has been inadvertently re-set to “recirculate”. Over the years, I helped a number of co-workers who were clueless about their constantly-fogged windows, and all of them had their HVAC systems set to “recirculate”.

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That comment always mystifies me. When I use recirculate or more often the max settings, the HVAC system works as a dehumidifier.

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That is true if somebody is using the A/C or the defroster, but if the controls are set for heat, then “recirculate” allows the condensation from breath and from wet shoes to form on the windows.

Ah, been a long time since I drove a vehicle with heat/defrost without AC. Now that I remember it in the 60s how the humidity from our breath, not to mention melting snow from our shoes, would fog up the windows.

If you are driving in below freezing weather, your AC condenser is not turning on no matter how you set it. Cold outside air, especially if the cold outside air is below freezing, has very little moisture in it, even if its relative humidity is 100%. But inside air even at 50% relative humidity has a lot of moisture in it and when it hits cold surfaces like windows, it condenses and freezes.

In the small enclosed space of a car, you add a lot of moisture to the air from breathing and perspiring. The HVAC will not de-humidify because the AC is not working, no matter the setting. If it did work, the moisture in the vehicle would freeze against the evap core and block any airflow through the HVAC system in short order.

BTW, not of this is related to the oil change unless someone there put your HVAC in recirculate.

The compressor on my Honda Accord turns on at below freezing temperatures?

Tester

You need to tell both of my vehicles that . Because they do activate the AC to keep windows clear .

If it does, the expansion valve in the evaporator core should be closed at any temperature below 40F so the compressor wouldn’t be doing anything. The compressor in your Accord is commanded on and off by the PCM so it shouldn’t be commanded on below 40F. But if you are seeing the compressor come on, I can’t argue with that.

Edit: I stand corrected, the 40F is based on inside the cabin temperature and not outside air so it could come on once the heater has heated up the cabin. But even with the AC on in recirc during cold weather, it did not clear out enough moisture in any of my vehicles, including my 97 Accord, to keep fog from forming on the windshield, so using outside air is still a valid suggestion.

Why does everyone recommend turning the AC on in the winter, if the compressor is doing nothing?

Tester

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@Tester, I edited my post. I have founf that when the outside air is below freezing, the AC is not needed but in all my current vehicles, that is not an option in defrost. Some still allow the AC to be turned off on the windshield/floor position.

Some vehicles, when the HVAC system is set to defrost, the AC compressor automatically turns on. No matter the temperature.

On my Honda, I have to manually turn the AC on. And the compressor turns on, no matter the temperature.

Tester

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That was true of my 97 Accord, which I no longer have, but the compressor was controlled by the PCM when the AC switch is turned on.

Pretty sure my 98 Dodge truck did that, compressor came on with defrost automatically.

As for the original question, I think I’d check the evaporator drain. Years ago, the techs plugged the cowl drain on my wife’s Camry when doing an oil change to keep the water from dripping on them while they were under the car.

The recent work is unlikely to be related to the moisture problem. Coincidence. Ask your shop to make sure the AC drain is clear. If it is and there’s water accumulating under the front carpet, either you have a plugged door drain or the heater core is leaking. If it’s the heater core that’s leaking, the “water” under the carpet is engine coolant, and will feel more slippery than plain rain water and will usually have a sort of sweet odor. On a Civic, I don’t think it’s the heater core, and the problem shouldn’t be overly difficult for your shop to resolve.