Defroster problem

My HVAC system has been working just fine. But the other day I had something odd happen........

I was driving north from LA to Reno, weather was cold (40) and rainy. I had the temp. set to 71 on automatic. When I got up to about 3000 feet it got several degrees colder outside, and quite suddenly my windshield and front side windows fogged up and then lots of condensation. I turned on the defroster but it wouldn't clear the windshield at all. I had to pull over and wipe down the inside windows. It did the same thing about 10 minutes later.

I don't see anything in the owners manual about how to set the defroster with the controls, other than just pressing the defroster button. I tried all kinds of different temp settings but nothing helped.

Wondering if anyone knows what caused this and if its a symptom of a problem with the system?

Thanks!

nvsteve wrote:

My HVAC system has been working just fine. But the other day I had something odd happen........

I was driving north from LA to Reno, weather was cold (40) and rainy. I had the temp. set to 71 on automatic. When I got up to about 3000 feet it got several degrees colder outside, and quite suddenly my windshield and front side windows fogged up and then lots of condensation. I turned on the defroster but it wouldn't clear the windshield at all. I had to pull over and wipe down the inside windows. It did the same thing about 10 minutes later.

I don't see anything in the owners manual about how to set the defroster with the controls, other than just pressing the defroster button. I tried all kinds of different temp settings but nothing helped.

Wondering if anyone knows what caused this and if its a symptom of a problem with the system?

Thanks!

The A/C compressor helps defrost the windshield by dehumidifying the air. However, the A/C compressor will not engage if the outside temperature is below 41*. That can really hamper defroster action, especially if the air inside of the car is very humid. That can happen if you have a lot of people in the car, or, if the inside of the car is wet from a leak.

I bet that is the reason it happened, I was wondering why the a/c compressor wasn't cutting in to help. The only odd thing is I was the only person in the car. Guess I'm full of hot air!

Thanks for the post!

Steve

nvsteve wrote:

I bet that is the reason it happened, I was wondering why the a/c compressor wasn't cutting in to help. The only odd thing is I was the only person in the car. Guess I'm full of hot air!

Thanks for the post!

Steve

I didn't want to say that Steve, LOL. Did you have anything wet inside the car, or was the carpet wet?

actually I didn't think to check if the carpet was wet. It might have been damp from the previous day when I had the car out in the rain (at NASCAR Fontana) with several passengers getting in and out of the car.

nvsteve wrote:

actually I didn't think to check if the carpet was wet. It might have been damp from the previous day when I had the car out in the rain (at NASCAR Fontana) with several passengers getting in and out of the car.

That would certainly contribute to the problem.

When the A/C shuts off there is often a large amount of humidity brought in from the cold condenser sweating. This compounded with just the right outside conditions will cause what happened to you. To clear it you could have tried cranking the heat (heat also lowers relative humidity) and fan on defrost. It still may have taken a few minutes to clear up though.

In my tuner I lowered the A/C shutoff temp to 32 to avoid this exact scenario.