Reading airconditioning gauges
Discussion
I posted this picture in a recent aircon thread but didn't really understand the reply I got.
Its a picture of my aircon gauges that I used to re gas our van, I understand the two outer scales, one is PSI and the other is BAR sor metric and imperial scales of pressure. But there are 4 inner scales and each relates to a different type of refrigerant gas. The reply I got was they are just to compensate for how hot or sold the day is when you are doing the re-gas.
I understand that the aircon pressure fluctuates with differences in temperature but you can't adjust the gauges in any way to set them for the current temp so what relevance are the inner scales when pressurising it up. Hope someone knows as its interesting to find out.
PS it was 20 deg outside in that picture when I did it 12 months ago and its still working perfectly today so I must have done something right (re-gas was needed as I changed the condenser).
PPS I'm not an aircon engineer just someone who likes to have a go at things.
Its a picture of my aircon gauges that I used to re gas our van, I understand the two outer scales, one is PSI and the other is BAR sor metric and imperial scales of pressure. But there are 4 inner scales and each relates to a different type of refrigerant gas. The reply I got was they are just to compensate for how hot or sold the day is when you are doing the re-gas.
I understand that the aircon pressure fluctuates with differences in temperature but you can't adjust the gauges in any way to set them for the current temp so what relevance are the inner scales when pressurising it up. Hope someone knows as its interesting to find out.
PS it was 20 deg outside in that picture when I did it 12 months ago and its still working perfectly today so I must have done something right (re-gas was needed as I changed the condenser).
PPS I'm not an aircon engineer just someone who likes to have a go at things.
The temperature scales are for different gasses with different saturation points (i.e a mix of both gaseous and liquid) at a given pressure.
The temperature/saturation is used for diagnostics to see whether the system is running properly, and whether there's internal issues in the system, insufficient airflow etc etc.
In your case the gauges are multi-gas, so you can use them on R22, R134A, R410 and another that I can't quite make out
The temperature/saturation is used for diagnostics to see whether the system is running properly, and whether there's internal issues in the system, insufficient airflow etc etc.
In your case the gauges are multi-gas, so you can use them on R22, R134A, R410 and another that I can't quite make out
The temp scale is nothing to do with the ambient temperature, it is at what temp the gas or liquid is on the relevant side. It is a rough guide but if the low side is at 30psi then the temp that the gas is at is about 4 Oc, from this you can work out the sub cooling and superheat of the system and ensure that it is working efficiently. You would also have to take a temp reading at the evaporator and the condenser then compare it to the gauge reading and the difference would be your super heat and sub cooling and from that you can work out the ideal evaporation and condensing pressure and that will indicate the health of the system. Eg low refrigerant = higher evaporation temp, high liquid pressure = blocked condenser or overcharge of refrigerant would lead to high condenser pressure. If that makes any sense.
jeebus said:
The temp scale is nothing to do with the ambient temperature, it is at what temp the gas or liquid is on the relevant side. It is a rough guide but if the low side is at 30psi then the temp that the gas is at is about 4 Oc, from this you can work out the sub cooling and superheat of the system and ensure that it is working efficiently. You would also have to take a temp reading at the evaporator and the condenser then compare it to the gauge reading and the difference would be your super heat and sub cooling and from that you can work out the ideal evaporation and condensing pressure and that will indicate the health of the system. Eg low refrigerant = higher evaporation temp, high liquid pressure = blocked condenser or overcharge of refrigerant would lead to high condenser pressure. If that makes any sense.
Indeed it does. Google is a great thing indeed.Apologies, you can identify what type of refrigerant is in a bottle or turned off system by knowing what pressure the refrigerant is at ambient temp.
Eg r134a @21 Oc is 71psi but r410a @21 Oc is 201 psi there must be liquid refrigerant present to get a correct reading. You would use a chart or comparator to get a more accurate reading, you could also use a digital gauge which are great for reading in temperature or pressure.
Eg r134a @21 Oc is 71psi but r410a @21 Oc is 201 psi there must be liquid refrigerant present to get a correct reading. You would use a chart or comparator to get a more accurate reading, you could also use a digital gauge which are great for reading in temperature or pressure.
Bear in mind that I’m not an aircon engineer, just a DIYer with the kit and a fleet of cars to practice on...
I don’t think the absolute pressure really matters in most cases. You fill the system by weight, not pressure. When the air con is running, you want the high side to be higher than the low side, but whether it is 7.8 bar or 11.3 bar depends on your compressor and refrigerant characteristics. Assuming you’ve got the right refrigerant, then there is little you can do. Clearly if the pressures are off the scale, something is badly wrong, but your system probably has exploded by then anyway.....
I don’t think the absolute pressure really matters in most cases. You fill the system by weight, not pressure. When the air con is running, you want the high side to be higher than the low side, but whether it is 7.8 bar or 11.3 bar depends on your compressor and refrigerant characteristics. Assuming you’ve got the right refrigerant, then there is little you can do. Clearly if the pressures are off the scale, something is badly wrong, but your system probably has exploded by then anyway.....
Basically you have two sides to a refrigeration system - the low pressure side (usually measured after evaporator and before intake into the compressor) which is connected to the 'Blue' gauge, and the high pressure side (red gauge) connected usually just after the Condenser
refrigeration gauges measure the relevant pressures in the system, and then the gauges will have some relevant temperature 'saturation' scales as well
so depending on the refrigerant (and you need gauges with the right scales for your refrigerant (or you could use a set of pressure/temperature tables) you would read the pressure indicated on the dials and then read across the needle to the appropriate scale and this will tell you the saturation temperature of the refrigerant at that pressure.
usually this information in conjunction with measuring the 'actual' temperature on the pipework at these key points will allow the engineer to look at superheating and sub-cooling which can let the engineer know if the system has faults such as over/under charged, blocked evap/condenser coils, TXV issues etc
refrigeration gauges measure the relevant pressures in the system, and then the gauges will have some relevant temperature 'saturation' scales as well
so depending on the refrigerant (and you need gauges with the right scales for your refrigerant (or you could use a set of pressure/temperature tables) you would read the pressure indicated on the dials and then read across the needle to the appropriate scale and this will tell you the saturation temperature of the refrigerant at that pressure.
usually this information in conjunction with measuring the 'actual' temperature on the pipework at these key points will allow the engineer to look at superheating and sub-cooling which can let the engineer know if the system has faults such as over/under charged, blocked evap/condenser coils, TXV issues etc
Ok....
I ask you to boil water... whats the boiling point ? 100 degrees ?
Okay I tell you that I can boil water at room temperatrue ? And I can, I tell no lies... Ill boil water at room temperatrue.
This is possible, If I have the water in a vaccum then the temperaturer that it boils at will drop.
Similarly if I close up the container that the water is in I could have the water remain as a liquid with the temperature above 100 degrees.
The liquid and gas stages of water are dependant on both temperatrue and pressure. This is something that features heavily in refrigeration.
Super heated means that it is still a liquid beyond the temperature of evaporation. And like wise sub cooled means that it is still a gas beyond the temperature of condensation.
All these principles need to be monitored, this is done through careful use of guages and understanding your system. You need to know the gas being used. By monitoring the gases you will be able to understand the system. and be able to identify and sort out any issues as they develop. A refridgeration system uses a compressor. This compresseor take in low pressure gas and compresses the gas to a higher pressure, this gas then passes through a condensor that turned it to a liquid. This liquid is then passed through an expansion valve to return it to a low pressure liquid. The liquid then passes to an evaporator that sucks the heat up to turn this liquid to a gas and it is then passed to the condensor and repeats. To understand you need to know the pressures and the temperatrues of the system. With a refrigerant at a pressure it will have a 'temperatrue' value.
So on the high line before the expansion valve. You have a valve that lets you connect to a guage. The guage then gives you a pressure, and that pressure will convert to a temperature with the tables that are related to the refrigerant. that temperatrue when compared to the actual temperatrue will give you a value. Same with the high pressure side. hence the need for the guages and a thermometer.
I ask you to boil water... whats the boiling point ? 100 degrees ?
Okay I tell you that I can boil water at room temperatrue ? And I can, I tell no lies... Ill boil water at room temperatrue.
This is possible, If I have the water in a vaccum then the temperaturer that it boils at will drop.
Similarly if I close up the container that the water is in I could have the water remain as a liquid with the temperature above 100 degrees.
The liquid and gas stages of water are dependant on both temperatrue and pressure. This is something that features heavily in refrigeration.
Super heated means that it is still a liquid beyond the temperature of evaporation. And like wise sub cooled means that it is still a gas beyond the temperature of condensation.
All these principles need to be monitored, this is done through careful use of guages and understanding your system. You need to know the gas being used. By monitoring the gases you will be able to understand the system. and be able to identify and sort out any issues as they develop. A refridgeration system uses a compressor. This compresseor take in low pressure gas and compresses the gas to a higher pressure, this gas then passes through a condensor that turned it to a liquid. This liquid is then passed through an expansion valve to return it to a low pressure liquid. The liquid then passes to an evaporator that sucks the heat up to turn this liquid to a gas and it is then passed to the condensor and repeats. To understand you need to know the pressures and the temperatrues of the system. With a refrigerant at a pressure it will have a 'temperatrue' value.
So on the high line before the expansion valve. You have a valve that lets you connect to a guage. The guage then gives you a pressure, and that pressure will convert to a temperature with the tables that are related to the refrigerant. that temperatrue when compared to the actual temperatrue will give you a value. Same with the high pressure side. hence the need for the guages and a thermometer.
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