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A/C when heat is on

I have a 2002 Honda civic, standard, that I bought second hand in March this year which is running great except the A/C all summer would just turn off randomly and then after anywhere from 10min to an hour later come back on. I had it checked out and they said it was a leak, filled it up and put the special dye and it worked great for a month then started again. When they checked it again there were no leaks, so assuming its the compressor. Being near winter I decided to leave it until next year but now I’ve noticed when I turn the front windshield defroster on and put the temp dial to heat, the A/C light comes on! Every time and it wont turn off. It doesn’t matter if I’ve put it all the way to heat or cold - if its on the windshield or windshield and foot vent the A/C is on. I think I can hear the A/C running too. If I change the dial from the windshield to the feet vents only or whatever the A/C stays on until I push the button to turn it off but it will turn off at this point. Any ideas???

The Honda turns on the AC whenever you move the control knob to Defrost setting. That is just the normal set up for the car. I had AC compressor issues and it turned out to be the AC switch on the dashboard was bad. This is pretty common in these Honda’s, mine is an '03 Civic.

Before the expense of replacing the compressor, have that dash switch checked or replaced. It was about a $100 bill, much less than a new compressor.

You need the AC to defrost the windshield. Specifically, you need to remove the moisture from the air. And that’s where the compressor comes in.
By the way, why are those guys thinking the compressor is leaking if they can’t see any dye coming out?
I’d want to peek at the evaporator. Since it’s in the evaporator housing, maybe that’s why they can’t see any leak.
Let me ask you another question: If you set the controls to blow in your face or at the floor only, can you turn the compressor on and off?
If yes, I’d say, leaks aside, the AC compressor is functioning correctly.

Sorry I think I didn’t word that well. They said there was no dye in any of the hoses and by the description from how the A\C comes on and off that it sounded like the compressor wasn’t turning on properly.
When I turn the controls on the floor only or on my face the A/C will stay on until I turn it off, but if I have it on the windshield it won’t turn off.

Thanks for your input!

So, there’s no dye visible on the hoses, but the AC isn’t cooling that well, right?
Did the shop check how much refrigerant was still in the system?
If it was low, somebody should keep looking for leaks.
Anyways, I still think the compressor is working correctly.

I have owned a newer Honda (08 Accord) and an older (99 Accord) that turned on the A/C with the defroster. Once the windshield was clear I would manually turn off the A/C. My 99 Accord was even simpler. Once the defroster was done clearing the windshield I could just push the A/C button and the A/C stopped running.

I dare say that your A/C light has ALWAYS come on with the defrost setting of your climate controls and you are only noticing it now since you are having other issues. Is your A/C an “automatic” system where you set the temperature or a manual one where you just adjust the controls? Are you keeping the A/C working very hard in the summer? I like my car cold in the summer but I discovered my newer Accord would ice up the condenser if I ran it too cold for too long on very humid days. Then I would have to wait 20 or 30 minutes without A/C to let the condenser thaw out so I could get some cooling again.

Running your A/C in the winter is a very good idea since many folks with leaks discover that, by not running the A/C for the entire winter, the seals dry out and the refrigerant can leak out of the system.

The A/C comes on in the defrost position in every car I’ve encountered, from the 1970s on up, foreign and domestic. Most of the older cars don’t advertise that this is happening with a light coming on, but it still does. This is totally normal. In temperatures near and below freezing, the light may still come on, but the A/C actually doesn’t run–the pressure in the system is either too low to engage the compressor or there is a temp sensor that makes the decision whether to run it or not. This too is normal.

Some A/C systems will run the compressor for a second or two whenever you use the system, whether the A/C is on or not. This is to lubricate the compressor and other seals by slightly circulating the refrigerant. Again, this is normal.

If you have your owner’s manual, look at the section for heating and cooling–it will probably describe these behaviors as well.

Most cars for 50 years runs the A/C when the defrost is on. It serves to lower the humidity and also keeps the seals fresh. It seems to me that since you added freon in the summer, all is working well now.