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Weird A/C Issue #5411940 04/24/20 11:13 AM
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timoboy Offline OP
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2012 Mazda 3 2.0 Skyactiv 6MT 167k

Between 60-70 degree weather, the A/C blows ambient air temp (65ish degrees) while on the freeway. At idle when that temp outside, it is reasonably cool, but not as cool as it should be.

When colder than 60 the a/c functons normally. When first started in the morning, and when in the 70s-80s outside it functions normally. Let the vehicle sit at idle in 75+ degrees yesterday, and no issues with cold (40-45 degree ) A/C temps.

Did a leak inspection. Found small leak at condenser/drier. Both are bare aluminum on this vehicle and showed corrosion from living near the coast. Replaced condenser, drier, o-rings, PAG46. Professional vacuum system and leave overnight-no leaks and recharge with exact weight/volume specified 134a-no change except even cooler air at idle and when hot/cold outside. Still very much "dead" in the 60-70 degree ambient temp range.

Manual A/C, no temp sensor on the dash/etc that would be a factor. Compressor cycles on for 12-16 seconds/off for 5-6 seconds when functioning normally. When malfunctioning seems to cycle on 5-6 seconds and off for a similar period of time.

At idle, high side PSI is the correct 2.2 times ambient air, low side ranges from 25-45 PSI, triggering the compressor on/off at both respective ends of that range

When the system is off, it takes 10 minutes for the low side and high side pressures to equalize. I'm reading this may or may not be too long, depending on the vehicle.


Looking at a bad expansion valve? In that temp range maybe the valve is not opeining all the way, shutting off the compressor prematurely and then taking several seconds to recover, hence warm air?


Weak compressor? At speed slipping and not charging adequately or not building pressure quickly enough after being commanded off/on by the pressure switch due to worn internals? Took it for a "spirited" drive at 75 deg yesterday and the A/C funtioned perfectly.

Fan controller? Fan seems to come on normally in tandem with the compressor clutch.

Any one ever experianced anything like this?

Last edited by timoboy; 04/24/20 11:33 AM.
Re: Weird A/C Issue [Re: timoboy] #5411971 04/24/20 12:07 PM
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JohnG Offline
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How about the outside air temperature sensor? Had some bad ones pop up with Cadillac during that time period.

Re: Weird A/C Issue [Re: timoboy] #5411972 04/24/20 12:08 PM
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mk378 Offline
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Intermittent problems are often hard to diagnose.

Testing while the system is working properly will generally reveal nothing.

If it is ever not cooling at idle, pull over and look under the hood if the compressor is turning, condenser fan running, and suction line cold. Pressure readings would be ideal here as well.

The main causes here are compressor clutch doesn't always engage, expansion valve sticking, and reheating from the heater. The last one you would find everything under the hood OK including the suction line is cold.

Re: Weird A/C Issue [Re: timoboy] #5411976 04/24/20 12:15 PM
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JTK Offline
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Does the system work when there's a real heat load on it, like when ambient temps are above 80F?


2019 Nissan Pathfinder SV
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Re: Weird A/C Issue [Re: JohnG] #5412008 04/24/20 01:22 PM
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timoboy Offline OP
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The only outside temp sensor also feeds the dash temp readout, and it is accurate. This is a bretty basic/bare bones economy car so just cable adjusted climate control.

I would like to try to catch the problem while it is happening, however it only really presents itself at freeway speed, I can try pulling over really quick and popping the manifold set on for readings.

The really hot times seem to be OK, I took it out yesterday between 75-80 (about as hot as it gets here) and it was ice cold. It's just got a real issue in the mid range.

Last edited by timoboy; 04/24/20 01:23 PM.
Re: Weird A/C Issue [Re: timoboy] #5412082 04/24/20 03:19 PM
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JohnG Offline
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How about the sun sensor on top of the dash?

Re: Weird A/C Issue [Re: timoboy] #5412206 04/24/20 06:49 PM
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WobblyElvis Offline
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Does this car have air blocking shutters in front the condenser? Malfunctioning?

Re: Weird A/C Issue [Re: timoboy] #5412510 04/25/20 06:23 AM
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GMBoy Offline
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Are the electric fans running?

Re: Weird A/C Issue [Re: timoboy] #5412518 04/25/20 06:37 AM
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CourierDriver Offline
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Ok, in my few years in HVAC I usually look for dirt, yes dirt is a big killer in HVAC,, dirty return air fins or condenser fins...If they are clogged you will have all kinds of problems. I was never trained on auto aircondiionters, but I do service my own cars, usually its always a low charge, easy fix if no obvious leaks...just charge with one of those cans from an auto parts store. ok, my 2 cents ...


I'd still like to have my 67 Beetle back....life was easy then..imho 2 quarts of oil roughly ,lol
No matter what time it is,its always time for a nap
Re: Weird A/C Issue [Re: timoboy] #5412641 04/25/20 09:59 AM
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tiger862 Offline
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Sounds like compressor is getting weak. There is a sensor on the back of compressor called AC control switch that goes out will cause a cycling. I don't know if you have that particular switch although I see you have a transducer.

https://www.carid.com/universal-air...html?singleid=2175875292&url=1175333


Tiger862
2018 Grand Caravan
Re: Weird A/C Issue [Re: timoboy] #5412663 04/25/20 10:19 AM
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JHZR2 Offline
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Is this a new condition? Do you have experience with it working properly before? Gut feel is that the highway use is a clue. Lots of rpms to help with compression, lots of airflow. Cool ambient.

How is expansion controlled in this one? I’m thinking perhaps an old/stuck/dirty orifice or txv results in backup and pressure cutout early at the compressor, and not enough refrigerant flow at the evaporator. The low ambient means it doesn’t have a lot of delta T either to drive it.

Have you looked at the expansion valve of whatever type is in there?

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