The 5 Characteristics of Refrigeration

I wanted to write a post to remind everyone how important it is to identify all 5 measurements of a refrigerant cycle and check all 5 components of a refrigerant system before you conclude what the issue is.

So, as a reminder, the 5 Measurements of the Refrigerant Cycle are … Low Pressure, High Pressure, Superheat, Subcool, and Delta T – (temp drop). And the 5 components of a refrigerant system are … Coil, Metering Device, Lineset, Condenser, and Compressor.

It is in my experience, it’s good practice to check all aspects of the components in the refrigerant cycle before you engage with the 5 measurements of the refrigerant cycle. Check the coil (drain, dirty, damage, airflow and all associated aspects related to the airflow from the filter to the cfm setting on the furnace). Nothing you can do with he metering device in the early stages of inspection. The condition of the lineset is a good idea (armourflex, kinks, any other damage or potential damage should be dealt with). Clean the condenser and check for damage or growing shrubs that inhibit its ability to do what it’s supposed to do. Check all wiring, the contactor, the capacitor, the motor, blade and direction of the blades. Unless you have a compressor that has completely failed, put your gauges on the system to start with the 5 measurements.

Every aspect and every part of the air conditioner system can change any or all of those measurements, but I am going to focus on the metering device. More specifically – the TX Valve. The Thermo-expansion valve. The valve that responds to the temperature of the suction header.

First, I want you to remember that refrigerant is a liquid. And like most other liquids, it does have a boiling point – a temperature at which it will boil and turn to steam/vapour. Water boils at 212 oF, but it will boil in a vacuum in room temperature. Same with refrigerant. Change the pressure and you can get 410A refrigerant to boil in a coil with 70 oF air. That’s a coil with 410A refrigerant at about 170 lbs of pressure turning to a steam/vapour using house temperature air.

Second, I want you to remember that this topic is about the temperature of the refrigerant, not the air passing over the coil.

In my class I have a couple of bottles of water to illustrate what volume does to the overall temperature of the refrigerant as it picks up the heat. Those of you who have been in my class are picturing it right now. For those of you who haven’t, I have 2 bottles of water. 1 1/2 full, and the other is typically full.

Throw each of the bottles into a microwave oven, one at a time, on high for 1 min and one of them will be warmer than the other. They both absorbed heat, but the one with less water feels hotter because there is less volume. Less volume also means it will absorb that heat easier and quicker. Put that water in a pot and bring it to a boil. It likely came to a boil pretty quick, but what happens when you add more cold water? It lowers the overall temperature of the water. And if you add enough water, it will stop boiling and remain in a liquid state for some time.

The bulb for the TXV can feel the temperature of the refrigerant in the coil as it leaves the evaporator. The bulb makes the TXV open and close allowing more or less refrigerant into the coil depending on the temperature of the refrigerant in the suction header. If it’s too hot, it’s likely absorbing too much heat out of the air which makes the coil freeze (bottle with less water). So, it will open the valve to allow more refrigerant into the coil to ‘cool’ the volume of refrigerant down. And subsequently, if it’s too cold (bottle with more water), it will have to much refrigerant for the temperature of the coil, so it will close the valve to find the perfect refrigerant temperature. Ultimately finding the perfect Superheat. A TXV is also known in the industry as a Constant Superheat Valve. It modulates the amount of refrigerant entering the coil to maintain the specific superheat it was designed to keep that coil at.

And that my friends, in brief, is what you need to keep in mind on your next service call as you try to determine if you have a TXV problem or not. Until next time – Happy Trails! (or something like that)