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My windshield won't defog

My A/C isn’t working, but my heater is. When I set the defogger for my windshield, air does come out but it’s not defogging. Any recommendations on how to fix this problem or reason why it may not be defogging?

In order for the defogging to work really well, you need the A/C compressor to be working, and–normally–the compressor does run when the defrost setting is selected. So…until you get the compressor fixed, you will not have really effective defogging.

However, in addition to the A/C compressor problem, there is the issue of the temperature of the air. You mentioned that air is coming from the defrost ducts, but you did not say whether it is hot air or not. What is the temperature of the air?

Since it is cold where I live, I have the hot air set. Would it make a difference if I have cold air coming from outside coming in instead? Would that help a little with the defogging of the windshield.

You want the air coming from your defrost ducts to be both hot and dry.
Hence, the need for the A/C compressor to be working, as well as the need to keep the temperature set on the highest setting.

Also…I hope that you are not using the HVAC system on the “recirculate” mode.
Every winter I see many cars with constantly fogged-up windows, and while this can be from other causes (including a leaking heater core), most of them are undoubtedly from recirculating the moist air inside the car.

Relating to the possibility of a leaking heater core…
Is there a strange odor in the air when you use the HVAC system?
Does the residue on the inside of the window feel somewhat oily?

If the answer to those questions is “yes”, then you most likely have a leaking heater core, which needs to be repaired a.s.a.p., in order to prevent some nasty respiratory problems for you and your passengers. Breathing aerosolized antifreeze is very hazardous to your health.

Thanks! I will look into this and definitely check to see if the A/C compressor is working.

If your system has a “recirculation” setting it will continue to recirculate the air without taking the moisture out. Make sure the button with the arraw going around on it is in the off position.

Recommendations? Fix your AC.

I’d fix the air conditioning, as others have said. If you let it go too long, it may cost more to fix, as components can be damaged by moisture or lack of use.

In the meantime, try to avoid tracking snow into the car. The more moisture you have in the car, the harder it will be to defrost.

In cold weather, you need to be on outside air, it is drier than inside air. The cold outside air holds very little moisture, even when its relative humidity (RH) is very high. As this cold air comes in and is warmed up by the heater, the RH drops dramatically so that it will absorb the moisture off the windshield.

If the outside air temp is below 40 degrees, the AC doesn’t make any difference as long as you are on outside air.

I did not get my first ac car until 91, and defrosters allways worked previously. Do you get plenty of warm air blowing out the duct? Warm air for the heater? and as Docnic said make sure you are on recirculate, and I believe opening a rear window as I do when fogging is a problem will help get rid of warm moist air and introduce cool dry air with minimal discomfort.

Barkydog, you meant NOT on recirculate didn’t you?

The A/C compressor won’t kick in at really low temperatures anyway, so the key is to use the fresh air setting vs recirculating.