A/C Pressure Test/Diagnosing in cold ambient temps

[EMT with a Yaris]

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).

[06YarisRS]

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 :drool: 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. :laugh:

https://i.imgur.com/K9w9AoQ.jpg

https://i.imgur.com/JYJbPw4.jpg

[tmontague]

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

[06YarisRS]

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. :laugh:

[toyotavios_11]

thx for the chart. i like DIY.

[EMT with a Yaris]

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!


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 :drool: 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. :laugh:

https://i.imgur.com/K9w9AoQ.jpg

https://i.imgur.com/JYJbPw4.jpg