QuestionWhat should the high and low pressures be on a 2005 Dodge Ram diesel air conditioner? Thanks
AnswerPhil,
The pressures inside your system will vary from day to day dependant upon what the temperature is outside the vehicle. Pressure and Temperature are relative in that if one raises so will the other. If one drops, the other will also. So your pressure readings on a day in which it is 95 degrees outside will be much higher than a day where it is only 65 degrees outside.
Here is how you can determine them.
High side:
Take a temperature reading of the ambient air outside. The best place to measure it is about 3 inches away from the condensor. (Located in front of the radiator) Let's say we have a reading of 90 degrees fahrenheit. Take 90 and add 35 degrees to it. This simulates the heat that would be getting carried through the system by the refrigerant. 90 + 35 = 125 degrees. Now take this 125 and compare it to a pressure/temperature chart (here is a link for a fairly user friendly one) http://www.csgnetwork.com/r134apresstempconv.html
at 125 deg. F your high side pressure will be reading 183 psig on your gauges. However your high side will fluctuate about 40-50 psig. If you watch you will see the pressure rise from 180 to about 225 and back down again as your condensor fan kicks on.
Low side:
Again temperature reading but this time of the interior of the vehicle, preferably the passenger floorboard area. (this is where your evaporator is) Let's say you read 80 degrees. From this you will subtract 30 degrees, this simulates the amount of heat being absorbed into the refrigerant through the evaporator) 80 - 30 = 50 degrees fahrenheit. Again plug this into the link I provided and you will find that your low side should be reading roughly 45psig on your gauges. This one will not fluctuate nearly as dramatically as your high side. It should float 3-5 psig in either direction but no more than that.
So your gauges will read 180 (fluctuating) on your high (red gauge on right side) and 45 on low side (blue gauge on left) on a 90 degree day WITH YOUR ENGINE RUNNING AND A/C ON.
If your low side is reading much lower than 45, that is one way of tellng that you have a leak somewhere in your system.
But remember, Pressure readings change day to day on the same vehicle. you HAVE to check the temperature before anything else and work from there.
I hope I was able to provide a satisfactory answer. If so, please remember to rate this answer. If I can do anything further, either now or in the future, please do not hesitate to ask. If you need me to break down the process even more, I would be happy to do so. (As an HVAC instructor, I enjoy seeing how far I can break it down so that everyone can understand it perfectly)
But thank you for the question and good luck in everything.
