Auto Air Conditioning & Heater Repair: ac refrigrant, degree day, temperature chart


Question
what should the low side pressure be for a 2002 volvo and a 1999 mustang 134a

Answer
Dennis,
Pressure and temperature are relative. If one goes up so will the other. So it is impossible for me to tell you what your pressure readings should be without knowing the temperature of the ambient air outside. It will be different today from what it will be tomorrow.
Here is how to figure it out though.
Take the ambient air temp and subtract 35 from it. Then cross reference this number to a pressure/temperature chart for the refrigerant you are using and that number you find is what you should read on your low side at idle.
example: if it is 90 degrees outside, subtract 35 (because this is the temperture difference factored in when figuring pressures for an air conditioner) that leaves 55. At 55 degrees the pressure for R134a will be roughly 51 psig. This is your low side reading.
For your high side you will take the ambient temperature and add 30 to it (forced convection condensor) then cross reference the number.
example: 90 degree day add 30 degrees = 120 degrees. At 120 degrees the pressure for R134a is roughly 170psig. This is yor high side reading at idle.
So on a 90 degree day your gauges will read low 51  high 170.
On an 80 degree day they will read low 39    high 145.
Here is a good site to convert if you want it.

http://www.csgnetwork.com/r134apresstempconv.html


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