Search the Community

I’ve read Mike’s comments on the AC compressor cycling, and tend to agree that it shouldn’t cycle if performing correctly. However, I’ve noticed mine will cycle with the heat on (defrost). Is this a normal function?

Here are all of the components of the 2nd Gen A/C system, and what they all do. First is the compressor. The refrigerant is compressed making it even hotter, it becomes a high pressure high temperature vapor. http://www.mopar1973man.com//isx97/Truck%20Stuff/Ryan's%20Dodge/Under%20Hood/AC/IMG_1471.JPG After turning into a high pressure high temperature vapor, the refrigerant goes through the condenser. The condenser has ambient air running through it which cools off the superheated refrigerant, so much so that the refrigerant turns back into a liquid. Nevertheless, the refrigerant is still pretty hot and remains at high pressure. http://www.mopar1973man.com//isx97/Truck%20Stuff/Ryan's%20Dodge/Under%20Hood/AC/Condenser.jpg Now we make the refrigerant cold. To do this, it goes through an orifice tube. The orifice tube (not to be confused with an expansion chamber) has an orifice that holds back the pressure in the condenser and also allows the pressure to build, if there wasn't a restriction from the orifice, the condenser would quickly lose all of its high pressure and wouldn't do it's job. The orifice tube allows a metered amount of flow to go through it, and then expands into the hose that goes to the accumulator, becoming very cold. One side will be hot, the other will be cold. It will also now be low pressure. This can be seen with an air compressor when you blow air out of a hose. The air expands instantly and is cooled, that is why the air feels so cold coming out of that air hose. http://www.mopar1973man.com//isx97/Truck%20Stuff/Ryan's%20Dodge/Under%20Hood/AC/Expansion%20Valve.jpg It then proceeds into the Accumulator or Dryer. This stores the freon and also has things in it to help dry out the freon to prevent any moisture from building up. http://www.mopar1973man.com//isx97/Truck%20Stuff/Ryan's%20Dodge/Under%20Hood/AC/IMG_1470.JPG The last step is the Evaporator. This is inside the cab and air is blown through it, giving you cold air out of your vents. Technically speaking, it is absorbing heat into the refrigerant which then turns the liquid refrigerant back into a low pressure gas as it warms. They get stuff built up in them, as mine has. http://www.mopar1973man.com//isx97/Truck%20Stuff/Ryan's%20Dodge/Interior/Dash%20and%20Vacuum/IMG_1192.JPG So now that the refrigerant is a low pressure hot gas, it is sent back to the compressor to compress it into a high pressure, very hot, gas that has much more heat to be released in the condenser. If it was a low pressure gas, there wouldn't be enough volume through the condenser to keep you cool, it would also not be hot enough to release enough heat to keep you cool. So you compress it to make it really hot, the condenser has a ton of heat it easily expels, and the refrigerant expands back into a low pressure fluid that is very cold, and you have an efficient a/c system. Ambient temp influence the pressures of the high and low side. Here are 2nd Gen Pressures, taken from http://articles.mopar1973man.com/2nd-generation-24v-dodge-cummins/27-hvac-heating-ventalation-and-air-conditioning/58-recharging-air-conditioning-with-r134a-freon Vent temps..