rswanny

I have a 1999 LS 400 with 186k miles. I just had the cam shaft and crank shaft sensors replaced as the car would turn over but not start. Seems to have resolved the issue. However the mechanic noticed that when the heat is on the a/c is running also. So he unplugged the A/C as it is winter here in Minnesota. Has anyone encountered this issue and know the cause of it?

timmy0tool

iTrader: (7)

if you have your vent setting on front windshield defrost, the AC will automatically turn on with the fan. this is normal, and useful for defogging the front windshield during cold weather. there is something in the AC properties that aid in defogging, and it's NOT the cold air that does it. you can have your heater on full blast and it will still defog with the AC on!

heat will always overpower the AC cold. i would have your mechanic reverse what he did.

sha4000

iTrader: (1)

timmy hit it on the head. For years I could never figure out why the A/C was on when I put the defroster on. I believe the A/C pulls the moisture out of the air to defrost the windshield quicker.

billydpowe

iTrader: (1)

you bet have him plug it back in....

msweber97

Id say hes not much of a mechanic! This is normal and has been for years have him plug it back in or do it yourself.....

SandyDT

I noticed this almost immediately in my 2003 ES300. The hubby mentioned what you guys did and also, if you have it set to automatic...it will attempt to keep the temp you have it set for if that requires heat or AC. I think that's how it works, any way.

Shmee

iTrader: (3)

lol, mother of god... Find a new mechanic.

I'm actually serious.
Someone who doesn't know the basics of car function I would not trust to do more than change may tires and even then double checking everything after they were done.

mappo

Maybe the OP means that the AC comes on without selecting defog mode? Which might mean the mode selector is busted and he's stuck in defog or defog/floor mode.

timmy0tool

iTrader: (7)

correct! if the AC is on even when the vent is NOT in defrost mode and pressing the switch does nothing, then there is something else wrong which is likely the switch or HVAC controller panel itself.

Kansas

Nope. The A/C can come when "Auto" mode is selected regardless of whether or not the HVAC is in defrost mode as long as the outside temperature is above a minimum ... something like 32 degrees Fahrenheit.

billydpowe

iTrader: (1)

I use auto all the time and mine works like Jim just said and I agree with the guys, find a REAL mechanic, yours is a beginner..... and auto keeps my windows clear also... because if I reach over and turn the AC off, they start clouding up... wow my brilliance keeps coming out.. (hehehe)

timmy0tool

iTrader: (7)

ah yes i type corrected! i rarely run the auto mode setting myself and am so used to manual climate controls on my older cars. thanks for the clarification .

sam12345

iTrader: (1)

Put on auto push ac button. Now you have auto temp control with ac always off. Hit auto again, now you have auto with ac always on (actually turns on when necessary)