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Old 08-04-2019, 07:16 PM   #1
jimmyrustler
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Member#: 419656
Join Date: Apr 2015
Vehicle:
2015 WRX STi
Lightning Red

Default 2015 STi AC issues in the hot AZ summer

Hi Nasioc,

I recently moved to Glendale, AZ and my beautiful lightning red STi with 98,000 miles on it is experiencing Arizona desert temps for the first time and the results are not so pleasant.

My AC is blowing hot air at idle!

Outside temps are in the 115's at the hottest part of the day and after a long idle or cruising around 80-85 my temp gauge gets up in the 75% range.

I'm running out to Autozone in a bit to buy refrigerant to do a recharge and also check system pressure, and i'm wondering, when this ultimately doesn't cut it, where else should I be looking?

I've browsed through a good number of discussions on A/C issues and it seems like its usually down to a dying compressor or the need for a recharge.

I haven't replaced the accessory belt yet in this car and I wonder if maybe it's slipping.

I want to improve cooling performance over-all and it seems like the Koyo Aluminum radiator is the best bolt on option. Is a bigger oil system with a cooler a possible consideration as well?

Thanks for the input.
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Old 08-04-2019, 11:09 PM   #2
jimmyrustler
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Member#: 419656
Join Date: Apr 2015
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2015 WRX STi
Lightning Red

Default

Increased low pressure side R134a pressure up to 55 psi at 110 ambient temp outside. I definitely felt a major improvement in AC temps at idle.

But tbh the more I read about temp gauge stuff the more it has me worried about my high temps. Thinking about replacing the thermostat and getting water pump checked out. Time for timing belt too maybe, and coolant flush.

Looking for any input
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Old 08-06-2019, 08:01 AM   #3
jasonwrx86
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Join Date: Jul 2017
Chapter/Region: MWSOC
Vehicle:
2018 WRX Limited
CWP

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Quote:
Originally Posted by jimmyrustler View Post
Increased low pressure side R134a pressure up to 55 psi at 110 ambient temp outside. I definitely felt a major improvement in AC temps at idle.

But tbh the more I read about temp gauge stuff the more it has me worried about my high temps. Thinking about replacing the thermostat and getting water pump checked out. Time for timing belt too maybe, and coolant flush.

Looking for any input
75% range that is pretty weird.
Even 100F degree days mine just sits in the middle in stop and go traffic.
Are your fans running correctly? How about coolant level and condition?
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Old 08-06-2019, 11:27 AM   #4
jimmyrustler
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2015 WRX STi
Lightning Red

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The fans do appear to be working when I check with the hood popped while stationary. Coolant level in the overflow tank has dropped enough now in my time owning the car that I have had to top it off from well below "LOW" to up to the "FULL" line TWO TIMES.

As far as the color of the coolant? It doesn't appear super murky but then again I haven't drained the whole system either, just popped off the radiator cap while cool to check. My oil never comes out gunky either, so I don't think i'm getting coolant in my oil.

Thanks for the reply mate!
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Old 08-06-2019, 11:59 AM   #5
Waddlz
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Join Date: Jul 2014
Chapter/Region: RMIC
Location: Brighton, CO
Vehicle:
2012 STi
SWP

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I can't comment on the AC issue, but i was having similiar issues with coolant temps. Turns out my thermostat was getting stuck and only partially opening.

I was seeing 237 coolant temps in 100 degree weather with the AC on. I could see the needle start to move up.

I have 80k miles on my 2012 so I figured it was time for a new thermostat. I took the old one out, and a new one, and put them in water in a pan to see if that was the issue. Sure enough, the new one started cracking around 170 temp while the old one was completely closed until 180 when it barely cracked open, and stayed there.

Once i swapped, I am now seeing no more than 205 coolant temps in 100 degree weather with the AC on.
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Old 08-06-2019, 12:32 PM   #6
jimmyrustler
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Member#: 419656
Join Date: Apr 2015
Vehicle:
2015 WRX STi
Lightning Red

Default

Quote:
Originally Posted by Waddlz View Post
I can't comment on the AC issue, but i was having similiar issues with coolant temps. Turns out my thermostat was getting stuck and only partially opening.

I was seeing 237 coolant temps in 100 degree weather with the AC on. I could see the needle start to move up.

I have 80k miles on my 2012 so I figured it was time for a new thermostat. I took the old one out, and a new one, and put them in water in a pan to see if that was the issue. Sure enough, the new one started cracking around 170 temp while the old one was completely closed until 180 when it barely cracked open, and stayed there.

Once i swapped, I am now seeing no more than 205 coolant temps in 100 degree weather with the AC on.
I don't have an AP so I can't see exact temps but this sounds just like my situation! I was looking at new thermostats on sunday. I wonder if the mishimoto low temp thermostat is a good choice or if sticking with OEM is better.

Now I just need to buy it and do the work before it gets stuck completely closed....
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Old 08-06-2019, 12:40 PM   #7
Waddlz
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SWP

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No. stick with OEM.

The mishimoto ones are garbage.

the only aftermarket thermostat I'd buy is RCM.
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Old 08-06-2019, 12:58 PM   #8
jimmyrustler
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Member#: 419656
Join Date: Apr 2015
Vehicle:
2015 WRX STi
Lightning Red

Default

Quote:
Originally Posted by Waddlz View Post
No. stick with OEM.

The mishimoto ones are garbage.

the only aftermarket thermostat I'd buy is RCM.
Will do man thank you!!
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Old 08-06-2019, 11:06 PM   #9
jimmyrustler
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Member#: 419656
Join Date: Apr 2015
Vehicle:
2015 WRX STi
Lightning Red

Default

I replaced the thermostat and gasket with an OEM one from the dealer down the street and refilled the coolant with the rest of my subaru blue and most of a jug of zerex asian blue from advanced auto.

Seems to be running much better!

I have pics of the old and new thermostat next to each other and the difference is night and day. I feel like I was a few thousand miles or less away from a completely stuck thermostat. Testing them both in boiling water and the difference was obvious as well, with the new one both opening further and more consistently and quickly.

I'm super happy with the outcome.


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