Is it better to turn off the AC a couple of minutes before turning the engine off, or just turn it off at the same time with the engine? I read that giving it some time to wind down allows the evaporator to empty out its refrigerant. Some say, that's not necessary in today's newer AC systems. Any thoughts?
Turning off AC before engine shutoff?
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Or just turn off recirculation a few minutes before you stop
Where I live it is HOT and humid right now, so the A/C is never shut off when I am in the car.
Originally Posted By: gregoron
Is it better to turn off the AC a couple of minutes before turning the engine off, or just turn it off at the same time with the engine? I read that giving it some time to wind down allows the evaporator to empty out its refrigerant. Some say, that's not necessary in today's newer AC systems. Any thoughts?
Not at all... It will "empty out" itself of refrigerant just fine without any intervention. Many have an "afterblow feature" that is automatic or can be turned on with service programming that will "blow dry" the evap when the car has been off for some time. This only works if the A/C has been off for some time to prevent further condensation on a cold evap. core. This has been hashed over many times on this forum.
Some might even be "SHOCKED" to find out some fairly recent VW's and others have "constant on" A/C compressors that CAN NOT ever be completely shut off. They just turn down their internal adjusting swash plate to the minimum and that is that. This is to simplify the A/C system and remove a failure point of a cycling clutch. Whether a cycling clutch A/C is a constant on orfice system or a cycling system - either way the clutch is often the first part to mess up/ or fail outside of refrig. leaks....
The point of the previous paragraph is that either use the A/C... or don't ... either way it isn't really a big deal in the scheme of things.... some systems may be more prone to smell, others not. But to obsess about it the way some do on this forum is kind of comical, at best.
BurrWinder
Is it better to turn off the AC a couple of minutes before turning the engine off, or just turn it off at the same time with the engine? I read that giving it some time to wind down allows the evaporator to empty out its refrigerant. Some say, that's not necessary in today's newer AC systems. Any thoughts?
Not at all... It will "empty out" itself of refrigerant just fine without any intervention. Many have an "afterblow feature" that is automatic or can be turned on with service programming that will "blow dry" the evap when the car has been off for some time. This only works if the A/C has been off for some time to prevent further condensation on a cold evap. core. This has been hashed over many times on this forum.
Some might even be "SHOCKED" to find out some fairly recent VW's and others have "constant on" A/C compressors that CAN NOT ever be completely shut off. They just turn down their internal adjusting swash plate to the minimum and that is that. This is to simplify the A/C system and remove a failure point of a cycling clutch. Whether a cycling clutch A/C is a constant on orfice system or a cycling system - either way the clutch is often the first part to mess up/ or fail outside of refrig. leaks....
The point of the previous paragraph is that either use the A/C... or don't ... either way it isn't really a big deal in the scheme of things.... some systems may be more prone to smell, others not. But to obsess about it the way some do on this forum is kind of comical, at best.
BurrWinder
I don't believe it will matter at all.
Originally Posted By: Cristobal
Where I live it is HOT and humid right now, so the A/C is never shut off when I am in the car.
This. The AC is left on when parked. And left in the on position when started. I dont understand the very dated and old fashioned way of turning off your AC before parking the car. If your car was made in the past 50 years, it will be fine leaving the AC on all the time.
As far as smelly systems, that must be a northern/cold climate problem. I have NEVER been in a car with a smelly system down here.
Where I live it is HOT and humid right now, so the A/C is never shut off when I am in the car.
This. The AC is left on when parked. And left in the on position when started. I dont understand the very dated and old fashioned way of turning off your AC before parking the car. If your car was made in the past 50 years, it will be fine leaving the AC on all the time.
As far as smelly systems, that must be a northern/cold climate problem. I have NEVER been in a car with a smelly system down here.
Originally Posted By: gregoron
Originally Posted By: 901Memphis
Or just turn off recirculation a few minutes before you stop
You mean let outside air come in? Is this to remove moisture in the vents and evaporator?
Yes. In operation, the evaporator ends up with condensation on it, just like a cold drink glass on a warm day. That moisture is what causes that puddle under your car.
The practice of shutting off the A/C ten minutes or so before home is supposed to allow the evaporator and its housing to come to ambient temperature while air is still blowing across it from the vent fan. The hope is that at least most of the condensate will evaporate before airflow goes to zero, minimizing the growth of mold.
The stinky-feet-smell seems to be more of a problem in areas where the A/C is only intermittently used, such as in the north. In climates that are consistently hot enough for the A/C to be in regular use, it may be that the evaporator does not sit -- warm and moist -- long and often enough for mold to form.
I was told that one reason automakers now install those HVAC air-filters is in order to minimize the collection of dust and debris on the evaporator and its housing. That crud holds moisture, impeding evaporation and exacerbating the mold problem.
Originally Posted By: 901Memphis
Or just turn off recirculation a few minutes before you stop
You mean let outside air come in? Is this to remove moisture in the vents and evaporator?
Yes. In operation, the evaporator ends up with condensation on it, just like a cold drink glass on a warm day. That moisture is what causes that puddle under your car.
The practice of shutting off the A/C ten minutes or so before home is supposed to allow the evaporator and its housing to come to ambient temperature while air is still blowing across it from the vent fan. The hope is that at least most of the condensate will evaporate before airflow goes to zero, minimizing the growth of mold.
The stinky-feet-smell seems to be more of a problem in areas where the A/C is only intermittently used, such as in the north. In climates that are consistently hot enough for the A/C to be in regular use, it may be that the evaporator does not sit -- warm and moist -- long and often enough for mold to form.
I was told that one reason automakers now install those HVAC air-filters is in order to minimize the collection of dust and debris on the evaporator and its housing. That crud holds moisture, impeding evaporation and exacerbating the mold problem.
Originally Posted By: BurrWinder
Originally Posted By: gregoron
Is it better to turn off the AC a couple of minutes before turning the engine off, or just turn it off at the same time with the engine? I read that giving it some time to wind down allows the evaporator to empty out its refrigerant. Some say, that's not necessary in today's newer AC systems. Any thoughts?
Not at all... It will "empty out" itself of refrigerant just fine without any intervention. Many have an "afterblow feature" that is automatic or can be turned on with service programming that will "blow dry" the evap when the car has been off for some time. This only works if the A/C has been off for some time to prevent further condensation on a cold evap. core. This has been hashed over many times on this forum.
Some might even be "SHOCKED" to find out some fairly recent VW's and others have "constant on" A/C compressors that CAN NOT ever be completely shut off. They just turn down their internal adjusting swash plate to the minimum and that is that. This is to simplify the A/C system and remove a failure point of a cycling clutch. Whether a cycling clutch A/C is a constant on orfice system or a cycling system - either way the clutch is often the first part to mess up/ or fail outside of refrig. leaks....
The point of the previous paragraph is that either use the A/C... or don't ... either way it isn't really a big deal in the scheme of things.... some systems may be more prone to smell, others not. But to obsess about it the way some do on this forum is kind of comical, at best.
BurrWinder
Thanks for that explanation. Yes, I think VW's run variable compressors that don't cycle on/off during operation. I replaced my AC compressor from my previous VW Jetta and found this out.
I've gained more respect on how an AC system works when my old VW's AC broke down and I had to fix it. It's not just a matter of replacing parts here and there. If one component fails, all of it fails. Then you have to evacuate, pull a vacuum, and replenish with exact amounts of fluids. I wouldn't want to go through that again with my new car hence I'm asking this somewhat banal question.
I guess I still believe in that myth that not turning the compressor off prior to shutting down the engine would ruin the compressor. I'm glad that this isn't the case. Still, I'd leave the recirc doors open when I park the car to vent off any condensation on the evaporator.
Originally Posted By: gregoron
Is it better to turn off the AC a couple of minutes before turning the engine off, or just turn it off at the same time with the engine? I read that giving it some time to wind down allows the evaporator to empty out its refrigerant. Some say, that's not necessary in today's newer AC systems. Any thoughts?
Not at all... It will "empty out" itself of refrigerant just fine without any intervention. Many have an "afterblow feature" that is automatic or can be turned on with service programming that will "blow dry" the evap when the car has been off for some time. This only works if the A/C has been off for some time to prevent further condensation on a cold evap. core. This has been hashed over many times on this forum.
Some might even be "SHOCKED" to find out some fairly recent VW's and others have "constant on" A/C compressors that CAN NOT ever be completely shut off. They just turn down their internal adjusting swash plate to the minimum and that is that. This is to simplify the A/C system and remove a failure point of a cycling clutch. Whether a cycling clutch A/C is a constant on orfice system or a cycling system - either way the clutch is often the first part to mess up/ or fail outside of refrig. leaks....
The point of the previous paragraph is that either use the A/C... or don't ... either way it isn't really a big deal in the scheme of things.... some systems may be more prone to smell, others not. But to obsess about it the way some do on this forum is kind of comical, at best.
BurrWinder
Thanks for that explanation. Yes, I think VW's run variable compressors that don't cycle on/off during operation. I replaced my AC compressor from my previous VW Jetta and found this out.
I've gained more respect on how an AC system works when my old VW's AC broke down and I had to fix it. It's not just a matter of replacing parts here and there. If one component fails, all of it fails. Then you have to evacuate, pull a vacuum, and replenish with exact amounts of fluids. I wouldn't want to go through that again with my new car hence I'm asking this somewhat banal question.
I guess I still believe in that myth that not turning the compressor off prior to shutting down the engine would ruin the compressor. I'm glad that this isn't the case. Still, I'd leave the recirc doors open when I park the car to vent off any condensation on the evaporator.
Originally Posted By: Lolvoguy
I shut mine off a few minutes before shutting the car off to dry ou the evaporator. If not, you might end up with that "moldy" smell the next time you start the a/c system.
seems to have kept my a/c system clean smelling
Better yet, run the system in "vent" mode a few minutes before shutting down will dry off the evaporator.
I shut mine off a few minutes before shutting the car off to dry ou the evaporator. If not, you might end up with that "moldy" smell the next time you start the a/c system.
seems to have kept my a/c system clean smelling
Better yet, run the system in "vent" mode a few minutes before shutting down will dry off the evaporator.
Originally Posted By: Lubener
Originally Posted By: Lolvoguy
I shut mine off a few minutes before shutting the car off to dry ou the evaporator. If not, you might end up with that "moldy" smell the next time you start the a/c system.
seems to have kept my a/c system clean smelling
Better yet, run the system in "vent" mode a few minutes before shutting down will dry off the evaporator.
Well, that would only work if the air outside is not humid and if the outside air is not humid, chances are that the air inside the car is not humid as well. Unless there is some physical activity going on
.
Also, in the recirc. mode and given some time, the air inside the car will actually be less humid than outside since the AC will be able to dehumidify it. Dehumidified air feels cooler than humid air. It's part of the reason the recirc. option is available in cars.
Whether you select outside air or recirc does not have any bearing on the evaporator temperature. It will still be very cold and therefore water will condensate on it.
I do pretty much the same as Lolvoguy does and it does help keeping the moldy smell away. It's a good practice IMO.
Originally Posted By: Lolvoguy
I shut mine off a few minutes before shutting the car off to dry ou the evaporator. If not, you might end up with that "moldy" smell the next time you start the a/c system.
seems to have kept my a/c system clean smelling
Better yet, run the system in "vent" mode a few minutes before shutting down will dry off the evaporator.
Well, that would only work if the air outside is not humid and if the outside air is not humid, chances are that the air inside the car is not humid as well. Unless there is some physical activity going on
Also, in the recirc. mode and given some time, the air inside the car will actually be less humid than outside since the AC will be able to dehumidify it. Dehumidified air feels cooler than humid air. It's part of the reason the recirc. option is available in cars.
Whether you select outside air or recirc does not have any bearing on the evaporator temperature. It will still be very cold and therefore water will condensate on it.
I do pretty much the same as Lolvoguy does and it does help keeping the moldy smell away. It's a good practice IMO.
Originally Posted By: KrisZ
Originally Posted By: Lubener
Originally Posted By: Lolvoguy
I shut mine off a few minutes before shutting the car off to dry ou the evaporator. If not, you might end up with that "moldy" smell the next time you start the a/c system.
seems to have kept my a/c system clean smelling
Better yet, run the system in "vent" mode a few minutes before shutting down will dry off the evaporator.
Well, that would only work if the air outside is not humid and if the outside air is not humid, chances are that the air inside the car is not humid as well. Unless there is some physical activity going on
.
Also, in the recirc. mode and given some time, the air inside the car will actually be less humid than outside since the AC will be able to dehumidify it. Dehumidified air feels cooler than humid air. It's part of the reason the recirc. option is available in cars.
Whether you select outside air or recirc does not have any bearing on the evaporator temperature. It will still be very cold and therefore water will condensate on it.
I do pretty much the same as Lolvoguy does and it does help keeping the moldy smell away. It's a good practice IMO.
No, that is not correct. It is outside air that you want - WITH THE COMPRESSOR OFF - and blown dry for awhile if you really want to monkey with this. The drying action happens when the compressor is off... otherwise it is best to use recirc. in operation as it doesn't keep "soaking" the evap with fresh WET air from outside. Once compressor is off, it's all relative and the surface "drying" occurs BECAUSE THEIR IS NO CONDENSATION ON THE EVAPORATOR OCCURING... On systems that are "auto" unless you are turning off compressor to save fuel or because it is cool enough outside, it is just best to use "auto" mode and pop compressor off if needed than constantly fidgeting with the system. I truly find in most vehicles it works best - and lasts the longest ( moving doors and valves constantly in manual does the system no good, either! ) We find this in the field as well...
BurrWinder
Originally Posted By: Lubener
Originally Posted By: Lolvoguy
I shut mine off a few minutes before shutting the car off to dry ou the evaporator. If not, you might end up with that "moldy" smell the next time you start the a/c system.
seems to have kept my a/c system clean smelling
Better yet, run the system in "vent" mode a few minutes before shutting down will dry off the evaporator.
Well, that would only work if the air outside is not humid and if the outside air is not humid, chances are that the air inside the car is not humid as well. Unless there is some physical activity going on
Also, in the recirc. mode and given some time, the air inside the car will actually be less humid than outside since the AC will be able to dehumidify it. Dehumidified air feels cooler than humid air. It's part of the reason the recirc. option is available in cars.
Whether you select outside air or recirc does not have any bearing on the evaporator temperature. It will still be very cold and therefore water will condensate on it.
I do pretty much the same as Lolvoguy does and it does help keeping the moldy smell away. It's a good practice IMO.
No, that is not correct. It is outside air that you want - WITH THE COMPRESSOR OFF - and blown dry for awhile if you really want to monkey with this. The drying action happens when the compressor is off... otherwise it is best to use recirc. in operation as it doesn't keep "soaking" the evap with fresh WET air from outside. Once compressor is off, it's all relative and the surface "drying" occurs BECAUSE THEIR IS NO CONDENSATION ON THE EVAPORATOR OCCURING... On systems that are "auto" unless you are turning off compressor to save fuel or because it is cool enough outside, it is just best to use "auto" mode and pop compressor off if needed than constantly fidgeting with the system. I truly find in most vehicles it works best - and lasts the longest ( moving doors and valves constantly in manual does the system no good, either! ) We find this in the field as well...
BurrWinder
Originally Posted By: BurrWinder
No, that is not correct. It is outside air that you want - WITH THE COMPRESSOR OFF - and blown dry for awhile if you really want to monkey with this. The drying action happens when the compressor is off... otherwise it is best to use recirc. in operation as it doesn't keep "soaking" the evap with fresh WET air from outside. Once compressor is off, it's all relative and the surface "drying" occurs BECAUSE THEIR IS NO CONDENSATION ON THE EVAPORATOR OCCURING... On systems that are "auto" unless you are turning off compressor to save fuel or because it is cool enough outside, it is just best to use "auto" mode and pop compressor off if needed than constantly fidgeting with the system. I truly find in most vehicles it works best - and lasts the longest ( moving doors and valves constantly in manual does the system no good, either! ) We find this in the field as well...
BurrWinder
I was replying to "run the system in "vent". I took it as keep the AC running and just switch to fresh air. Which would not dry off the evaporator.
No, that is not correct. It is outside air that you want - WITH THE COMPRESSOR OFF - and blown dry for awhile if you really want to monkey with this. The drying action happens when the compressor is off... otherwise it is best to use recirc. in operation as it doesn't keep "soaking" the evap with fresh WET air from outside. Once compressor is off, it's all relative and the surface "drying" occurs BECAUSE THEIR IS NO CONDENSATION ON THE EVAPORATOR OCCURING... On systems that are "auto" unless you are turning off compressor to save fuel or because it is cool enough outside, it is just best to use "auto" mode and pop compressor off if needed than constantly fidgeting with the system. I truly find in most vehicles it works best - and lasts the longest ( moving doors and valves constantly in manual does the system no good, either! ) We find this in the field as well...
BurrWinder
I was replying to "run the system in "vent". I took it as keep the AC running and just switch to fresh air. Which would not dry off the evaporator.
I turn off my ac, but leave vent on high and cold until it stops blowing cold. I'm sure my wife doesn't do that in the Corolla. Neither one has issues, but my civic is a 96 and hers is a 13. I've seen recommendations by service techs to shut off the ac a few minutes before the car to prevent those smells. I live in Southern California.
I guess it doesn't matter if I leave the AC compressor and fan on, or turn it off, before I shut off the engine. It won't damage the compressor or put a load on the engine when starting again.
As for the mold prevention, I can just leave the vent open (i.e. recirc off) after I turn off AC or engine to allow moisture from the evaporator escape outside.
As for the mold prevention, I can just leave the vent open (i.e. recirc off) after I turn off AC or engine to allow moisture from the evaporator escape outside.
I have never shut an AC system off on any vehicle I have owned with factory AC before shutting the engine down. Now I did back in the 70s with a hang on AC system in a 73 Nova 6 cylinder. Chevy didn't install factory air on that engine back then. Not enough power I was told.
In every vehicle I have had since the late 90s, the compressor doesn't engage until after the engine is running.
Never had a problem with a musty odor either.
In every vehicle I have had since the late 90s, the compressor doesn't engage until after the engine is running.
Never had a problem with a musty odor either.
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