# Recent podcast, puzzled by caller w A/C question? **URL:** \ **Category:** The Show\ **Created:** [January 11, 2025, 11:37pm UTC](https://community.cartalk.com/t/recent-podcast-puzzled-by-caller-w-a-c-question/198673 "2025-01-11T23:37:10Z")\ **Posts on this page:** 19\ **Page:** 1
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [January 11, 2025, 11:37pm UTC](https://community.cartalk.com/t/recent-podcast-puzzled-by-caller-w-a-c-question/198673/1 "2025-01-11T23:37:10Z")
Husband disagrees w/ wife: - Wife: You should only turn on the AC at idle, never at speed. - Husband: I’ll turn it on at any speed I want, if I’m hot. Wife believes the inertial force of engaging AC at speed damages the compressor, the belt, and/or the engine. Ray says there is some merit to this. But isn’t the AC compressor cycling on and off whenever the AC is on, speed or idle? ---
**Author:** ![davesmopar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/davesmopar/32/41750_2.png) [@davesmopar](https://community.cartalk.com/u/davesmopar)\ **Post date:** [January 12, 2025, 12:11am UTC](https://community.cartalk.com/t/recent-podcast-puzzled-by-caller-w-a-c-question/198673/2 "2025-01-12T00:11:59Z")
It would be more rpm based then mph based… Regardless, I will use my AC anytime I am hot, and remember that when you turn on your defrost, it turns on the AC compressor to help defrost/dehumidify the frost/fog on the windshield… plus it keeps the compressor from lying dormient and the seals drying up, so it is better to use the compressor then to not use it, and since a lot of AC systems go well over 100K-200K + miles, I am not worried about it… ---
**Author:** ![texases](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/texases/32/862_2.png) [@texases](https://community.cartalk.com/u/texases)\ **Post date:** [January 12, 2025, 1:33am UTC](https://community.cartalk.com/t/recent-podcast-puzzled-by-caller-w-a-c-question/198673/3 "2025-01-12T01:33:03Z")
System is designed to handle all normal use, turn it on whenever you want. ---
**Author:** ![Nevada\_545](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nevada_545/32/41232_2.png) [@Nevada\_545](https://community.cartalk.com/u/Nevada_545)\ **Post date:** [January 12, 2025, 2:07am UTC](https://community.cartalk.com/t/recent-podcast-puzzled-by-caller-w-a-c-question/198673/4 "2025-01-12T02:07:18Z")
Initial compressor clutch engagement for the day can be harsh due to refrigerant oil from the lines settling into the compressor. Some vehicles alleviate the hash “clunk” by engaging the compressor clutch during start-up while cranking the engine (less than 400 rpms). The harsh engagement shouldn’t harm the compressor, but I prefer to switch the system on while at idle. ---
**Author:** ![ChrisTheTireWhisperer](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/christhetirewhisperer/32/34798_2.png) [@ChrisTheTireWhisperer](https://community.cartalk.com/u/ChrisTheTireWhisperer)\ **Post date:** [January 12, 2025, 3:44am UTC](https://community.cartalk.com/t/recent-podcast-puzzled-by-caller-w-a-c-question/198673/5 "2025-01-12T03:44:17Z")
> [@davesmopar](#): > > Regardless, I will use my AC anytime I am hot, and > remember that when you turn on your defrost, it turns > on the AC compressor to help defrost/dehumidify the > frost/fog on the windshield Why do I get so much argument when _I_ explain the above, on other car forums and blogs? The other participants typically insist that the compressor engages only for aircon, and not for defogger, simply because the blower doors direct the air differently for the two different modes. And don’t tell me it’s “how I go about explaining it”, because there’s just no gettn through stupid in some circles. ---
**Author:** ![davesmopar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/davesmopar/32/41750_2.png) [@davesmopar](https://community.cartalk.com/u/davesmopar)\ **Post date:** [January 12, 2025, 2:12pm UTC](https://community.cartalk.com/t/recent-podcast-puzzled-by-caller-w-a-c-question/198673/6 "2025-01-12T14:12:11Z")
I am not going to speculate why people do what on other forums, I have not seen the threads nor am I going to read them… For modern(ish) ICE vehicles only with OEM AC, don’t care about the others… lol Just tell them to go out to the vehicle and start it, pop the hood (doesn’t matter what order lol) and then turn on the dang defrost, go look under the hood and watch the ac compressor to see what it does… I’m sure there are exceptions to the rule… ---
**Author:** ![VDCdriver](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/vdcdriver/32/30_2.png) [@VDCdriver](https://community.cartalk.com/u/VDCdriver)\ **Post date:** [January 12, 2025, 3:29pm UTC](https://community.cartalk.com/t/recent-podcast-puzzled-by-caller-w-a-c-question/198673/7 "2025-01-12T15:29:34Z")
> [@davesmopar](#): > > I’m sure there are exceptions to the rule… EVs and PHEVs utilize an air-to-air heat pump for heat, air conditioning, and defrosting. There is no connection to the engine on PHEVs. ---
**Author:** ![davesmopar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/davesmopar/32/41750_2.png) [@davesmopar](https://community.cartalk.com/u/davesmopar)\ **Post date:** [January 12, 2025, 3:32pm UTC](https://community.cartalk.com/t/recent-podcast-puzzled-by-caller-w-a-c-question/198673/8 "2025-01-12T15:32:33Z")
> [@VDCdriver](#): > > > [@davesmopar](#): > > > > I’m sure there are exceptions to the rule… > > EVs and PHEVs utilize an air-to-air heat pump for heat, air conditioning, and defrosting. There is no connection to the engine on PHEVs. That is why I said this… > [@davesmopar](#): > > For modern(ish) ICE vehicles only with OEM AC, don’t care about the others… lol I knew they were different… ---
**Author:** ![MikeInNH](https://avatars.discourse-cdn.com/v4/letter/m/a587f6/32.png) [@MikeInNH](https://community.cartalk.com/u/MikeInNH)\ **Post date:** [January 13, 2025, 4:07am UTC](https://community.cartalk.com/t/recent-podcast-puzzled-by-caller-w-a-c-question/198673/9 "2025-01-13T04:07:16Z")
> [@davesmopar](#): > > and remember that when you turn on your defrost, it turns on the AC compressor to help defrost/dehumidify the frost/fog on the windshield Not all cars. Surely doesn’t do it on my Highlander or wife’s Lexus. I have to turn on the AC. Had this discussion years ago with my sister-in-law who owned a Civic. Her Civic DID turn the AC on when defrosting windshield, but my wife’s then Accord didn’t. Not sure why Honda didn’t the same feature in each vehicle. ---
**Author:** ![ChrisTheTireWhisperer](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/christhetirewhisperer/32/34798_2.png) [@ChrisTheTireWhisperer](https://community.cartalk.com/u/ChrisTheTireWhisperer)\ **Post date:** [January 13, 2025, 5:07am UTC](https://community.cartalk.com/t/recent-podcast-puzzled-by-caller-w-a-c-question/198673/10 "2025-01-13T05:07:03Z")
I think the issue here is terminology: “AC” and “DEF(og)” are simply blower and duct positions. Both, in probably 90 percent of conventional non-hybrid, nonelectric ICE powered vehicles, the same compressor clutch engaged for either aircon or defog/defrost modes. ---
**Author:** ![davesmopar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/davesmopar/32/41750_2.png) [@davesmopar](https://community.cartalk.com/u/davesmopar)\ **Post date:** [January 13, 2025, 2:13pm UTC](https://community.cartalk.com/t/recent-podcast-puzzled-by-caller-w-a-c-question/198673/11 "2025-01-13T14:13:47Z")
> [@MikeInNH](#): > > Not all cars. > [@davesmopar](#): > > I’m sure there are exceptions to the rule… … … … ---
**Author:** ![texases](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/texases/32/862_2.png) [@texases](https://community.cartalk.com/u/texases)\ **Post date:** [January 13, 2025, 2:16pm UTC](https://community.cartalk.com/t/recent-podcast-puzzled-by-caller-w-a-c-question/198673/12 "2025-01-13T14:16:33Z")
> [@MikeInNH](#): > > Surely doesn’t do it on my Highlander or wife’s Lexus I’m surprised. Both Lexus vehicles we’ve owned do that. Odd. Do you not leave the climate control in “automatic “ mode? ---
**Author:** ![MikeInNH](https://avatars.discourse-cdn.com/v4/letter/m/a587f6/32.png) [@MikeInNH](https://community.cartalk.com/u/MikeInNH)\ **Post date:** [January 13, 2025, 2:20pm UTC](https://community.cartalk.com/t/recent-podcast-puzzled-by-caller-w-a-c-question/198673/13 "2025-01-13T14:20:48Z")
> [@texases](#): > > Do you not leave the climate control in “automatic “ mode? No. That might be the difference. My 98 Pathfinder had that option and it would automatically turn on AC for defrost. But in normal operating mode - NO…I had to turn the AC on manually. ---
**Author:** ![Purebred](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/purebred/32/46796_2.png) [@Purebred](https://community.cartalk.com/u/Purebred)\ **Post date:** [January 13, 2025, 2:25pm UTC](https://community.cartalk.com/t/recent-podcast-puzzled-by-caller-w-a-c-question/198673/14 "2025-01-13T14:25:54Z")
Back to the original question. In as much as my vehicles are only turning around 2100 RPM at 70MPG, I don’t think that will hurt the AC . In the 80s a lot of small vehicles turned the compressor clutch on and off. I had an ‘84 Rampage, purchased new, which was a pickup version (think El Camino) of the Dodge Charger, which in turn was based on the Omni. With the 5 speed manual transmission you could feel it cycling. A friend with a Ford Escort could feel it in his car too. ---
**Author:** ![MikeInNH](https://avatars.discourse-cdn.com/v4/letter/m/a587f6/32.png) [@MikeInNH](https://community.cartalk.com/u/MikeInNH)\ **Post date:** [January 13, 2025, 3:15pm UTC](https://community.cartalk.com/t/recent-podcast-puzzled-by-caller-w-a-c-question/198673/15 "2025-01-13T15:15:33Z")
> [@Purebred](#): > > . In the 80s a lot of small vehicles turned the compressor clutch on and off. AC systems have improved significantly since the 80’s. ---
**Author:** ![davesmopar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/davesmopar/32/41750_2.png) [@davesmopar](https://community.cartalk.com/u/davesmopar)\ **Post date:** [January 13, 2025, 3:31pm UTC](https://community.cartalk.com/t/recent-podcast-puzzled-by-caller-w-a-c-question/198673/16 "2025-01-13T15:31:16Z")
> [@texases](#): > > > [@MikeInNH](#): > > > > Surely doesn’t do it on my Highlander or wife’s Lexus > > I’m surprised. Both Lexus vehicles we’ve owned do that. Odd. Do you not leave the climate control in “automatic “ mode? The automatic climate control may be the difference, I have not checked it on my truck, but I know that both manual HVAC Corollas (02-06) and 09 Vibe/Matrix all turned the AC on with the defrost mode, I will have to see on the 17 Corolla and my truck… I know we had this discussion on this forum a while back, just don’t remember all the details… ---
**Author:** ![MikeInNH](https://avatars.discourse-cdn.com/v4/letter/m/a587f6/32.png) [@MikeInNH](https://community.cartalk.com/u/MikeInNH)\ **Post date:** [January 13, 2025, 3:34pm UTC](https://community.cartalk.com/t/recent-podcast-puzzled-by-caller-w-a-c-question/198673/17 "2025-01-13T15:34:52Z")
> [@davesmopar](#): > > I have not checked it on my truck, but I know that both manual HVAC Corollas (02-06) and 09 Vibe/Matrix all turned the AC on with the defrost mode That’s the opposite of my 98 Pathfinder and wifes 07 Lexus. In manual mode defrost the AC does NOT turn on. ---
**Author:** ![davesmopar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/davesmopar/32/41750_2.png) [@davesmopar](https://community.cartalk.com/u/davesmopar)\ **Post date:** [January 13, 2025, 3:47pm UTC](https://community.cartalk.com/t/recent-podcast-puzzled-by-caller-w-a-c-question/198673/18 "2025-01-13T15:47:35Z")
Not manual mode, but manual climate control, full manual only… You seem to be talking about manually controlling your auto climate control… ---
**Author:** ![MikeInNH](https://avatars.discourse-cdn.com/v4/letter/m/a587f6/32.png) [@MikeInNH](https://community.cartalk.com/u/MikeInNH)\ **Post date:** [January 14, 2025, 1:49am UTC](https://community.cartalk.com/t/recent-podcast-puzzled-by-caller-w-a-c-question/198673/19 "2025-01-14T01:49:37Z")
> [@davesmopar](#): > > You seem to be talking about manually controlling your auto climate control We never turn the Auto Climate Control on. My Highlander doesn’t have that feature. My 05 4runner never had that feature either. Only vehicle I ever owned that had that feature was my 98 Pathfinder. Only vehicle my wife ever owned that had this feature is her 07 Lexus.