Prevent A/C from engaging when using defrost?
- Thread starter StillLearning
- Start date
The a/c is enabled to dehumidify and aid in clearing the windshield. Do some searches and get a refrigerant recharge with adapter and gauge. I've found that once the refrigerant pressure drops below a certain point, additional o-rings don't seal as well adding to the leaking. Give it a charge, get the pressure up and see if it performs and holds.
I recently paid $300 for a vacuum evacuation and refill with dye to find the leak. My advice is to do the same and tide you over to spring and get it properly repaired or else keep topping it off with auto store refrigerant until it eventually dies.
I dirive winter beaters and actually require ac to be working. If not........my breathing and just one more person or the dog and the windscreen fogs up. Fix your AC by putting flouescen dye in, and then recharge it with the no frills can of r-134a. Do not by the magic can with the additives in it.
Not sure why you want to do that because the mechanism of defrost is dehumidify the air before hitting your windshield. To dehumidify you cool it to condense the air's water, drip it out of the air, and then heat it up to dry it. Without running AC it is just like blowing air at the windshield that's already very cold, and condense more water on it.
If you can't afford to fix it yet just run heat, but it will have to wait till the engine warms up.
If you can't afford to fix it yet just run heat, but it will have to wait till the engine warms up.
Only if you are running on recirculate. In theory, air from outside, then heated, then cooled again against the windshield still has the same dew point as when it was on the other side of the windshield, so no fogging. Now sometimes you do get some recirculated interior damp air pulled through, or my favorite is dry snow blown off the hood and sucked into the air vent! That will frost the windshield with or without AC functioning, but with full heat, its gone in a few moments.
My Focus had a manual blend box, so you could run it on defrost and feet, just in the right spot so the AC wouldn't kick on.
With me alone in the car, there would be no frost anywhere without AC running. In the mornings, if a bunch of snow got in the cowl, the trick is to run it on full cold with a window cracked until the coolant warms up, to blow snow through the HVAC as snow, then flip to max heat to get through few moments of fogging and clear it quickly and then run as normal.
If the car was full of wet soggy kids and skis, then the rest of the windows would fog, but running the AC isn't helping that really either. The solution is crack a window and just let the high humidity air out and bring in more dry heated air, as the AC at -10C can hardly run anyways so its not doing much.
No, the outside air in the rain can be near 100% relative humidity, and cooling will condense the water in the AC evaporator (refrigerant evaporate and the water in the air condense), and then when you heat it up it will be much dryer.
You can use outside air to dry your windshield only if the outside air (snow) is dry cold air not moist cold air (rainstorm).
JTK
$100 Site Donor 2025
Like said, you'll live without functioning a/c it in terms of w/s defrost, but it's going to be like livin' in the old days. There are anti fog products you can clean the inside of the glass with to help.
There's no getting away from the fact that HVAC work is expensive. I saw a video a week or so ago with a later model Honda HR-V that had ~60-70K miles on it believe, and a bad a/c compressor that sent debris through the system. The shop could not find an aftermarket replacement compressor and had to go through Honda. The shop's cost for the new a/c compressor was over $1300. With a system flush, new condenser, etc, it was a $3500 job. The dealer wanted over $6K to do it.
There's no getting away from the fact that HVAC work is expensive. I saw a video a week or so ago with a later model Honda HR-V that had ~60-70K miles on it believe, and a bad a/c compressor that sent debris through the system. The shop could not find an aftermarket replacement compressor and had to go through Honda. The shop's cost for the new a/c compressor was over $1300. With a system flush, new condenser, etc, it was a $3500 job. The dealer wanted over $6K to do it.
I should've stated that, with heat only, you only have fogging problems on the windshield if you use recirculate. Any amount of heating lowers the relative humidity of the fresh air, so with the air flow of the fan, fogging or frost isn't an issue. Also the other factor is that the glass does get heated as well, so even at 100% humidity exterior air, the dew point is higher inside the front windshield because it is warmer, so it doesn't fog.
In my experience from -30F to 90F+ in the many cars I've had without AC, you can get a clear windshield without much difficulty. Sometimes with a full car, you need to crack a window to keep the flow of air at much lower relative humidity air moving fast up the windshield, but I've never been unable to see well enough to keep driving, using just heated air in winter, or just ambient air in the summer, in defrost mode.
Last edited:
- Joined
- Jul 17, 2025
- Messages
- 32
This probably doesn't apply, but on my 06 Altima, you put on the defrost. the a/c light comes on, you hit the a/c switch, and the a/c goes off, Doesn't defrost as well, 'cause the air isn't dried, but it works better than nothing.
There is a "cabin hack" to alter the compressor behavior in the defrost/defog mode, here a couple of videos concerning some honda models.
Howeveeer... however one needs to make sure that the AC compressor actually cuts out .
There is some ambiguity in the cr-v manuals thru the years and there may be more variations of odd behavior (the light may not come on although the AC will start...or the AC may or may not be able to be turned on/off in the defrsot mode...or whatever blah there was also in the owner's manuals)...
So first do the hack but then open the hood and observe the compressor clutch in the various positions of the knob/push buttons to make sure.
The "hack" is reversable they say and there are some self-diagnostic procedures for the AC system in the service manuals too.
And there is always the option for removing a fuse or the relay as other participants suggested.
Hope it helps some.
Howeveeer... however one needs to make sure that the AC compressor actually cuts out .
There is some ambiguity in the cr-v manuals thru the years and there may be more variations of odd behavior (the light may not come on although the AC will start...or the AC may or may not be able to be turned on/off in the defrsot mode...or whatever blah there was also in the owner's manuals)...
So first do the hack but then open the hood and observe the compressor clutch in the various positions of the knob/push buttons to make sure.
The "hack" is reversable they say and there are some self-diagnostic procedures for the AC system in the service manuals too.
And there is always the option for removing a fuse or the relay as other participants suggested.
Hope it helps some.
That, and you would have to secure the compressor connector someplace out of the way as well.
I just want to thank everyone for the replies. There was some very helpful info. Unfortunately "Life" happened shortly after I posted and I did not have a chance to follow up.
@Nukeman7 thank you for the pic of the relay location. I am sure I would have located it, but that came in clutch and saved me a bunch of time I would have spent in the rain trying to find it on the day I pulled it. In reply to your second post, the high pitch sound was very consistent regardless of whether the clutch was engaged or not. The comprssor was also starting to "clunk" a little when engaging, so as suggested, I am sure the compressor is tired.
As was mentioned, the defrost doesn't defog the windshield as well without the drying of the a/c, but it is much better than nothing and works just fine once it starts throwing heat. Brings me back to the days of driving my parents cars that did not even have a/c when I was younger. I find cracking open a window or two helps a lot when you have passengers contributing moisture inside the cabin.
I could technically afford to fix the a/c correctly, but on a 19 year old car with over 200k miles, I dont really want to put a ton of money into it, especially with my wife wanting me to "cull the fleet."
I was able to find a can of super tech refrigerant at Walmart without the stop leak. The plan will be to try adding it once the weather warms up a little. I will try to update this post with the results for what it may be worth.
@Nukeman7 thank you for the pic of the relay location. I am sure I would have located it, but that came in clutch and saved me a bunch of time I would have spent in the rain trying to find it on the day I pulled it. In reply to your second post, the high pitch sound was very consistent regardless of whether the clutch was engaged or not. The comprssor was also starting to "clunk" a little when engaging, so as suggested, I am sure the compressor is tired.
As was mentioned, the defrost doesn't defog the windshield as well without the drying of the a/c, but it is much better than nothing and works just fine once it starts throwing heat. Brings me back to the days of driving my parents cars that did not even have a/c when I was younger. I find cracking open a window or two helps a lot when you have passengers contributing moisture inside the cabin.
I could technically afford to fix the a/c correctly, but on a 19 year old car with over 200k miles, I dont really want to put a ton of money into it, especially with my wife wanting me to "cull the fleet."
I was able to find a can of super tech refrigerant at Walmart without the stop leak. The plan will be to try adding it once the weather warms up a little. I will try to update this post with the results for what it may be worth.
- Joined
- Jan 8, 2026
- Messages
- 48
Had to do this in my wife's car for a couple years until we got rid of it. One $40 can a year from Wal-Mart was enough to get it through the summer each time. Far better than the several hundred to diagnose and replace whatever was causing the leak.
I'm guessing it's the electric clutch bearing on the compressor that is making the noise. You can put a shorter belt on it that skips the a/c compressor.
Similar threads
