Weird A/C Issue

[timoboy]

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?

 

[JohnG]

How about the outside air temperature sensor? Had some bad ones pop up with Cadillac during that time period.

 

[mk378]

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.

 

[JTK]

Does the system work when there's a real heat load on it, like when ambient temps are above 80F?

 

[timoboy]

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.

 

[JohnG]

How about the sun sensor on top of the dash?

 

[WobblyElvis]

Does this car have air blocking shutters in front the condenser? Malfunctioning?

 

[GMBoy]

Are the electric fans running?

 

[CourierDriver]

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 ...

 

[tiger862]

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

 

[JHZR2]

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?

 

[timoboy]

As the weather gets hotter I've had some changes to report: As of now parts replaced: Condenser (Denso) (Original was leaking, no change with replacement) Dryer (Denso) Expansion Valve/TXV (Denso) (no change with replacement) A/C Pressure switch (OEM Used from low mile car) (Original tested good but had access to low mile one so swapped anyway) Compressor and clutch assy with proper PAG oil (OEM used from 12k mile car) (no change with replacement) Freon 2-3 times. Weighing out exact amount per Mazda TSM, used high end vacuum pump for 45 mins each time putting system in a vacuum. No leaks. Tested evaporator core temp sensor/resistor. In spec per MAZDA TSM Vehicle has no heater core valve. It has manual A/C so no sun sensor either. Its a pretty basic system. Both blend doors are actuating inside the heater box (this car only has 2, one for temp dial and one motorized flap for recirc/outside air). Might possibly be able to get colder vent temps by completely limiting flow of coolant to heater core at speed? Once warmed up, compressor only runs for 5 second intervals. The condenser fan only briefly turns on at idle, for such a brief time that it only gets up to speed before being triggered off. Sounds very odd. This now occurs at all times except first start (idle and driving). Compressor builds pressure to 175PSI, disengages, and then re-engages at 150PSI. This appears to be in spec. This translates to approximately 5 seconds on 5 seconds off. The end result of this is VERY cold perfect air from the vents when the compressor is running, and almost IMMEDIATELY warm air from the vents when the compressor cuts off. Speed doesn't matter, idle etc its the same no matter what at this point. Average temp from this process is in the 59-65 degree range from the vents. Every other vehicle I've driven has once gotten going at speed, produced consistent cool air with no temp variations at the vents. What would cause existing air in the evaporator to warm up almost instantaneously? On a recent 100 degree day, the A/C performed almost the exact same as it has on 65 degree days! VERY cold vent temps when running and warm temps when not, averaging out to upper 50s. On a lark, I brought over a friend's Mazda, 2006 Mazda5 5MT. Vehicle exhibited the same 5 second on, 5 second off compressor cycling. A/C was standard Mazda: mediocre but consistently cool in temp from the vents (50 degrees). I know Mazda hasn't figured out A/C, a family 97 Miata and 96 MPV had similarly poor A/C since new. However all vehicles would put out a consistent steady temp from the vents, be it not very cool. At this point the only remaining components in the system are the evaporator (possible clog)? or the ECU itself. Cabin air filters replaced and when I did so I visually looked at the evaporator fins and they are clean. The inside of the old compressor was perfect and no one has ever attempted to use stop leak etc so I think the entire system to be clean internally. Any thoughts greatly appreciated! I love this car, but will probably go ahead and sell if I can't straighten this out. When I first got this thing it had amazing A/C, almost as good as Toyota, certainly better than any Mazda I've ever had. I've got alldata with all factory specs to go off of and nothing has thus far tested bad or out of range. Shops here (SoCal) have zero diagnostic abilities. I could throw $200 diags and recharges at it at 4-5 places but it would not result in anything but no problem found. We simply do not have skilled automotive techs at any price in Southern California.

 

[Nick1994]

Originally Posted by timoboy

We simply do not have skilled automotive techs at any price in Southern California.

Chris142 (A/C guy on here) is in SoCal

 

[A_User55555]

"When malfunctioning seems to cycle on 5-6 seconds and off for a similar period of time" You need to find out what is shutting off the compressor. From my understanding, compressors get shut off when the evap temp is too low, low pressure is too low, or high pressure is too high. Do you have a scan tool? I don't think 5 seconds of compressor time is enough to cool a cabin. On my Cadillac (I know its different) the AC Compressor stays on most of the time and I have Ice cold air.

 

[another Todd]

What are you getting on the low side gauge? 175 on the high side seems low to me, might be low on refrigerant, but there are more knowledgeable AC guys on here like Chris142 as above.