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Old 12-23-2018, 01:08 AM   #1
EMT with a Yaris
 
Drives: 2010 Toyota Yaris - Sedan 4 Do
Join Date: Oct 2018
Location: Bergen County, NJ
Posts: 7
A/C Pressure Test/Diagnosing in cold ambient temps

Question is:
If the ambient temperature (car parked outside since I don't have a big enough garage to work in) is between 35-40 f (around 0-4c) what pressure should the car be having?

Service Manual states:
When the refrigerant volume is correct, the
gauge reading indicates as follows:
Low pressure side:
0.15 to 0.25 MPa (1.5 to 2.5 kgf/cm2)
High pressure side:
1.37 to 1.57 MPa (14 to 16 kgf/cm2)
HINT:
Pressure varies in accordance with certain
conditions (outside air temperature, sunlight
and wind).
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Old 12-23-2018, 07:06 AM   #2
06YarisRS
 
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Interesting question. I just went through this. Here is a snippet from my service manual and one from a 'generic' site. The upper 1/2 of the second image shows the pressures by temperature. It's too early in the am for me to do the math but if the relationship between temp and pressure is linear, you could extrapolate the data to get a rough idea of what pressures are required. There is no doubt that I have too much in mine as I'm getting spec pressures but at a considerably cooler ambient temp than published, so I will be testing my system again in the spring/summer and adjusting the amount of R134 accordingly. I am going to try to get my garage above 60 F with my 240V cube heater, but I'll have to pick a 'warmish' day. My garage isn't insulated - 1/2 of it is a poly film paint booth - but it's doubtful I'll be able to get it warm enough do an accurate assessment until much warmer weather arrives. The above said, I did read on one seemingly reputable website that you should never recharge your system under 60 - 65 F. Since your conditions are similar to mine, it might be advisable to just undercharge your system to keep it sealed, then adjust in summer. The other option of course is to take your car to a friend's heated garage or if your car is being serviced, ask the shop owner if you can pop in and check your pressures after it's been in there and warmed up a bit. Just make sure his back is turned if you have to release a bit of R134.



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Last edited by 06YarisRS; 12-23-2018 at 10:00 AM.
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Old 12-23-2018, 11:19 AM   #3
tmontague
 
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I used the above charts as well and they seemed to work well for me

I'm assuming they dont want you refilling in sub zero temps as it can lead to over charging the system if you are not aware of pressure changed in relation to ambient temps
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Old 12-23-2018, 01:23 PM   #4
06YarisRS
 
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Quote:
Originally Posted by tmontague View Post
I used the above charts as well and they seemed to work well for me

I'm assuming they dont want you refilling in sub zero temps as it can lead to over charging the system if you are not aware of pressure changed in relation to ambient temps
Precisely - to the best of my knowledge.
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Old 12-25-2018, 07:34 AM   #5
toyotavios_11
 
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thx for the chart. i like DIY.
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Old 12-26-2018, 10:16 AM   #6
EMT with a Yaris
 
Drives: 2010 Toyota Yaris - Sedan 4 Do
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Thanks 06YarisRS looks like I now have an excuse to leave jersey winter weather to go somewhere warm down south just to recharge the A/C! I've seen that table chart before as well and was thinking of just scaling it to my current amb temps, then re checking as it gets warmer. Happy Holidays Everyone!


Quote:
Originally Posted by 06YarisRS View Post
Interesting question. I just went through this. Here is a snippet from my service manual and one from a 'generic' site. The upper 1/2 of the second image shows the pressures by temperature. It's too early in the am for me to do the math but if the relationship between temp and pressure is linear, you could extrapolate the data to get a rough idea of what pressures are required. There is no doubt that I have too much in mine as I'm getting spec pressures but at a considerably cooler ambient temp than published, so I will be testing my system again in the spring/summer and adjusting the amount of R134 accordingly. I am going to try to get my garage above 60 F with my 240V cube heater, but I'll have to pick a 'warmish' day. My garage isn't insulated - 1/2 of it is a poly film paint booth - but it's doubtful I'll be able to get it warm enough do an accurate assessment until much warmer weather arrives. The above said, I did read on one seemingly reputable website that you should never recharge your system under 60 - 65 F. Since your conditions are similar to mine, it might be advisable to just undercharge your system to keep it sealed, then adjust in summer. The other option of course is to take your car to a friend's heated garage or if your car is being serviced, ask the shop owner if you can pop in and check your pressures after it's been in there and warmed up a bit. Just make sure his back is turned if you have to release a bit of R134.



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