Automotive Air Conditioning Information Forum (Archives)

Provided by

We've updated our forums!
Click here to visit the new forum

Archive Home

Search Auto AC Forum Archives

Burst of warm air from AC when car slows down/stops

satz on Fri January 29, 2010 12:31 AM User is offline

Year: 2007
Make: Mazda
Model: CX7
Engine Size: 2300T
Refrigerant Type: R134
Ambient Temp: 80
Country of Origin: Australia

hi all

My car's AC produces a short burst of warm air (measured with digital probe thermometer at up to 20C / 70F) as the car slows down (eg for a roundabout, or when you come to a stop). This happens most often when the car is driven after being parked say for an hour or so.

The air from vents becomes noticeably warm, and 'smells' like outside air.

I use 'fresh air' setting, and fan speed about 3 (out of 6). Coolest temperature setting and 'face' vent direction

my car has had this peculiar problem since new, and the service dept at mazda says it's "Normal"! in fact they did replace the AC compressor and regassed the system, which helped a little with overall cooling, but there's still the problem with the warm air bursts.

I've never had this on any previous car (even brand new ones)

Please let me have some ideas of what could be wrong...

TRB on Fri January 29, 2010 11:03 AM User is offlineView users profile

Not familiar with this vehicle. Things I would check are refrigerant level & pressures. Compressor clutch gap. Some vehicles computer will kick out the compressor clutch at slow RPM's such as when being at a stop light. Might check if your clutch is disengaging inadvertently.


When considering your next auto A/C purchase, please consider the site that supports you:

ice-n-tropics on Fri January 29, 2010 4:10 PM User is offline

How's summer time south of the equator?
First of all:
For lowest air temp move the air supply to recirculation, not fresh.

Mazda is known for poor actuation/sealing of the blend air door which allows some hot air from the heater to mix with the cold air from the evaporator coil
You can block a hot water hose from or to the engine to check this out

If you have a vane rotary compressor, just get use to punk idle cooling or add a condenser fan for a small improvement
Ga'day mate

Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy. How To Air Condition Your Hot Rod

TRB on Fri January 29, 2010 4:48 PM User is offlineView users profile

I agree with ice-n-tropics that you should be running in re-circulation mode for the best cooling possible. Even in normal mode @ 80 degree ambient you should still be having cold air in my opinion.


When considering your next auto A/C purchase, please consider the site that supports you:

satz on Sat January 30, 2010 4:31 PM User is offline

hi guys

thanks for the responses so far. Summer downunder has been pretty hot (35-38C maximums) with little or no rain...

Agree with you that the colder air does come by using recirc, but I'm still concerned about what could be causing the short burst of warm air (2-3 seconds) when the car slows down.

It feels like outside air is coming in, uncooled. ALmost like the compressor has switched off for 2-3 seconds.



NickD on Sun January 31, 2010 7:25 AM User is offline

Did you have this car since new? Was it always like that or is this just a problem that has started? Knowledge like this distinguishes the difference between an engineering or a maintenance problem that has just recently started. If charge levels are good, can always be a debris problem in restricting air flow either through the condenser or evaporator. In tree loaded Wisconsin, a blower motor is more like a leave chopper than a blower. And those insects building up on the condenser that causes pressures to rise that automatically kill the compressor. Sometimes, well many times, your system needs a good cleaning.

satz on Sun January 31, 2010 6:22 PM User is offline

hi nickD

I've had the car since new, and it has always done this warm air burst. I've cleaned the condensor (that's the radiator at the front, right?), as well as the pollen filter.

Symptoms continue to be:

1. outside, unairconditioned air, enters for a few seconds as the car slows down, or comes to a stop
2. happens mostly in the first few minutes of driving, especially after the car has been parked for a little while

I suspect it could be something to do with underbonnet heat (after all it's a turbo petrol engine) and doesn't have the best venting for the heat to escape.



BugMan on Mon February 01, 2010 1:22 PM User is offline

If you can confirm that the compressor stays engaged the whole time, I wonder if the condensor is getting a blast of super-heated air from the turbo and preventing heat removal from the condensor.

satz on Mon February 01, 2010 4:38 PM User is offline

hi bugman

interesting idea which I hadn't thought of.

however in mycar, the turbo is behind the engine block (which runs across the car). But your comment did get me wondering whether perhaps the condensor fan is not pulling enough air through the condensor, so when the car slows down heat from the engine/radiator is going in the reverse direction through the condensor....

Although having said that, it also produces warm air for a short burst even when slowing down from 100kmh to 90 kmh...

btw, is there any easy way to check whether the compressor is actually staying engaged the whole time (as the car slows down)?



NickD on Tue February 02, 2010 10:03 AM User is offline

Three of our vehicles have a green LED on the climate control panel that is in parallel with the compressor clutch coil, don't you have that? Really don't need one on my motorhome with a York, when that goes off, like someone turning off a rock crusher DeVille has too much soundproofing, no light, but can tell with the radio off when it switches on and off. Can connect a test lamp in parallel with your AC magnetic clutch if nothing else works for you.

How does your AC work otherwise? Read again where you were told this problem is normal. Tim could post a circuit diagram, but the odds of US cars being the same as yours is nil. Was really shocked how different cars are in Venezuela or Colombia, wouldn't mind having those far simpler cars here, but illegal to import them here. Could be some Australian law for that "feature".

TRB on Tue February 02, 2010 10:17 AM User is offlineView users profile

First off the Mitchell wiring diagrams I have access to are copyright protected. Not really proper to post them here but you can purchase their information fairly cheap on a per vehicle basis. Not sure if Alldata or Mitchell list non US designed vehicles as my program only provides vehicle makes which were design for the US market.

Mittchell & Alldata link.


When considering your next auto A/C purchase, please consider the site that supports you:

ice-n-tropics on Tue February 02, 2010 12:03 PM User is offline

What model compressor do you have. Is it a variable displacement model which might temporarily destroke when decelerated?

Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy. How To Air Condition Your Hot Rod

satz on Tue February 02, 2010 5:00 PM User is offline


I do believe it is a variable - displacement model, but I'm not sure whether it's meant to 'destroke' when deccelerating....

In fact, I'm not sure what 'destroke' means.

I do know that it is meant to (and does) shut off the compressor under full throttle acceleration.



bohica2xo on Wed February 03, 2010 12:35 PM User is offline

Drive by wire jap can. You only think you are in control...

The blend & fresh air doors are electric servos controlled by a computer - they are not fast to respond, so it is unlikely the air doors are moving suddenly.

The fact that it happens anytime you shave 10kph off of the speed indicates it is a software action.

Drive by wire cars have all sorts of odd quirks. Every time some idiot thinks up a new wiggle, it gets added to the code pile. All of the DBW cars I have driven are very sensitive to the slew rate of the potentiometer they call a "gas pedal". The faster you move the pot, the more the system ignores it.

Stomp the accelerator @ 20mph, and it will hesitate every time. "Are you sure? Do you really want to go THAT much faster?" "Click yes to proceed.." On the other hand, roll your foot purposefully to the floor - and the tires smoke - or the stupid traction control cuts the throttle for you.

Pay attention to how fast you lift your foot, and how far to make this happen. It is probably an emission related bit of PCM code, since it only happens when the car is in hot restart. Mazda is famous here in the US for issues with the evap cannister & control valves. This is something that affects the drivability in exactly the same part of the drive cycle. Mazda says it is ok, because the PCM does not post a DTC.

You may be able to keep it from shutting down the compressor if you lift a bit more gently, or a little less. In other words, quit driving like a brit in the roundabouts.


"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

NickD on Thu February 04, 2010 5:44 AM User is offline

The key word is control or more appropriately the lack of it and we are sure losing it. Played with Windows 7, it may have some software corrections over Vista, but noticed even more the lost of control over Vista, that has less control than XP, that has less control then Win98, with all less control than DOS. Kind of liked my Jap cars in the 80's with a real on off switch for the compressor, a linear cable operated blend and recir door. If driving by a real stinky open spreaded manure farm, did learn I could crank down the temperature control on my DeVille to 60 and eventually, the recir door would close. But by that time, the interior of the car smelled strong with manure. Wasn't a problem with a manual recir door.

Recall when the automatic chokes first came out, which was one of the first loss of control items, darn things never did work right, but at least you could buy a manual choker kit. Somehow these guys think a spring or some dingbat software program is smarter than you are, but they call it convenience. Sure isn't convenience when you have problems with this crap.

mikeden on Sat February 06, 2010 4:50 AM User is offline

There may be debris or bug that is building up outside your car “condenser”, this is the part that is like a mini-radiator mounted in front of your car radiator, try to clean this with a soft brush also, spraying with pressurized water will do. This may improve your car air-conditioning problem.

TRB on Sat February 06, 2010 2:47 PM User is offlineView users profile

Cleaning the condenser of debris is a good idea. But be careful not to bend over any of the fins or you will make you issue a lot worse!

1 post and 1 spam link, nice. At least mikeden tried to offer some input so we'll leave it for now.


When considering your next auto A/C purchase, please consider the site that supports you:

NickD on Sat February 13, 2010 12:48 PM User is offline

Salt did state his "characteristic" did exist since his vehicle was new and that is dealer stated this "characteristic" is normal. It's an Australian vehicle that is unique to the American market, and none of us have access to his circuit diagrams to verify what is causing this characteristic. Was suggested he connect a test lamp to the compressor clutch coil so he can determine if his electronic control system is disabling his compressor during slowing down or when stopped. The only time he is experiencing this characteristic.

So cleaning the condenser was not suggested, can also be debris between the radiator and the condenser or other air flow problems, but that would trip the high pressure cut off if he even has one. Can also be a firmware issue, only Mazda can change that. If satisfaction cannot be acquired from your dealer, should have the option to contact the vehicle manufacturer directly.

Edited: Sat February 13, 2010 at 12:55 PM by NickD

Back to Automotive Air Conditioning Forum

We've updated our forums!
Click here to visit the new forum

Archive Home

Copyright © 2016 Arizona Mobile Air Inc.