Refrigerant Lines

Choose the correct answer…

Correct answer is liquid line warm. suction line cool

You must be studying for your NC test Bruce. I know that one is on it. You should do well.

How many of my fellow Inspectors know which of the refrigerant lines carries the subcooled freon to the evaporator coil? Is it the suction line (Big) or the liquid line (small)

Please explain why you say that subcooled freon is sent to the evaporator coil? I assume you are talking the line that carries the freon from the condensor unit to the expansion device which is in the evaporator (air handler) unit.

I know but I ain’t tellin.

It is the liquid line and it is warm. The term subcooled is in relation to the overall technical characteristics of freon and the system.

This is why many tests are wrong when asking about “how the lines should feel to the inspector” The subcooled liquid line is actually warm in reality.

Datz cause “hot and cold” in HVAC is “relative”.

How about this one.
Which line should have a filter drier on it?

liquid line, and that would be a bi-directional one on a heat pump.

how about this one

When the outside fan on a newer carrier/bryant heat pump is observed turning off during heating mode and the compressor keeps running, is this always a defrost cycle?

I’ve only worked on yorks which fire up before the fan comes on. Is there another cycle I don’t know about?

Newer carrier/bryant with R410 will cycle off the outside fan to control head pressure. It will appear to be entering the defrost cycle excessively but its not really. It will only happen during low-load conditions, ie. 45-50F outside.

When I noticed this on my units a few years ago it was after a power outage so I thought the defrost boards had fried. I could not find a service guy anywhere that knew how they worked, they all said both units had a bad board. I ended up talking to the Bryant engineer (this took some creative phone work to get past the gate keepers) and we talked for an hour about heat pumps. The power company had already agreed to pay for the repairs but I ended up not even needing a service call. I just happened to be outside near the units that day and noticed this cycling.

“Sub-cooling” is when the refrigerant temperature is cooled lower than the temperature which the refrigerant condenses back to a liquid.

It by no means, means it’s cool.

The condensing temperature of an R-22 unit on a warm day is 129 degrees F. That is not cool! Sub-cooling is when it is < 129.

A filter/dryer can be installed on either line.
A suction filter/dryer is used to clean up a unit after compressor failure or other refrigerant contamination. It will not be installed on the large line of a heat pump because that is the discharge line in the heat mode. Instead it is installed inside the unit, after the reversing valve.

Try this. What is the device that looks like a dryer on the discharge line between the compressor and the reversing valve or condenser coil (if an A/C)?

So many times I see people that put on only suction line driers which really don’t do crap. What do you think happens in that drier after a temp change ,and what do you think happens to head pressure after time when you put on two driers?


good job Bruce! :slight_smile:

Jeffrey, suction line dryers have a specific purpose.

The head pressure drops right?

If you put on two dryers, and the suction line dryer gets clogged with contaminants (which is its intended purpose), it’s supposed to be removed, along with all the contamination.

Can anyone let me know any good study guides for A/C part of the national test

Trick question try this one guys.

Under what conditions can you see frost on the small liquid line of a standard split system condensing unit. No heat pump

At what point in time is this suction line dryer to be removed and or replaced