Refrigerant line coil

Here is a question I’ve always wanted more information on from you HVAC gurus.

When you find an AC unit installed with an extra coil of refrigerant line, why does the coil need to be horizontal? Is it just to help oil find its way back to the condenser/compressor? And is there any amount of extra coil which would be considered too much?

That is a improper oil trap created in that suction line and the bigger the trap the more oil is prevented from returning to the compressor. That is not the kind of trap you want big or little.

There is a exceptable type P-trap installed in a suction line but it is placed in the line just as it exits the A-coil box and it is used when the condensing unit is installed above the A-coil such as the A-coil in a basement and the condenser at ground level a good distance between the two

So this coil of refrig line is being used as an oil trap? Does it make any difference what the distance is? Because the A coil is just to the right in the photo and the condenser is just outside the foundation wall to the left. Probably about a five foot distance between the two.

No difference on the distance as long as the A-coil is the same level or higher such as a attic install. The lines were probally a pre-charged line set and they did not stretch them out as they should have.

So is this always a defect when there is an extra coil? I don’t see it often but I’ve never read about it being a defect.

There are drawbacksto pre-fab linesets - they are just a convenience for the installer.

Thanks for the info guys. Good stuff. :slight_smile:

Thank You. That is very interesting information.

This line set is placed in a horizontal position so it “will not” create an oil trap.

Just in case someone thinks this is a defect, it is not. It is installed in accordance with equipment manufacturer’s instructions.

HVAC systems should be designed to use the least quantity of refrigerant as possible otherwise problems arise. These pre-charge line sets increase the volume of the refrigerant needed for operation and can be problematic.

If the extra coil was vertical then it would trap oil and be considered a defect?

But either way, the extra coil is not the best installation and can lead to problems.

Are those correct?

Cameron, if the extra coil is vertical it would be very problematic when refrigeration velocity fell during low load conditions.

This is not a cut and dry, right or wrong.
The article posted indicate some of the reasons that they may not be desirable but it can also be noteworthy that commercial ice machines are designed with a specific line set if they use a remote condenser and if you modify it, you screw it up!

The article is basing its opinion upon installers that don’t use certified HVAC technicians to start up the equipment once it’s installed. These line sets are sealed and you simply bolt them onto the indoor and outdoor unit (breaking the seal). This eliminates having to evacuate the line set with a vacuum pump, eliminates potential water and air contamination, etc. but in any case in HVAC technician should evaluate the startup to ensure proper installation and charge.

As Charley pointed out, there’s a lot of different ways you can install an HVAC split system. If you have the condensing unit on the roof and it’s too high, you have to modify the piping design to ensure proper velocity to lift the oil back up to the compressor. If a startup technician isn’t available to do this job, you don’t have a clue what you just installed.

Any dip across the crawlspace of the refrigeration line causes a potential oil trap. It is noteworthy to put in your report but is not necessary to listed as a defect unless you know for a fact it is. And there’s no way to tell the oil level in a compressor without cutting it off and dumping the oil out.

Thanks David, that’s really good information to know.

That pic is strange as the loops in that line set do appear to be verticle not horizional the pic appears to be looking down into a cavity I must be getting old

I squatted down a little to get the shot. The coil was hanging just below a duct at the ceiling.

Ok but was the coils in the line set vertical or horizontal

also extra line, can be so for hard to access units (hanging units) etc., to give them a little free play when repairing or replacing.


I called it out for a lack of supports anyway, it’s only support was a water shut off valve it was resting on.


Cameron…is that a panned/floor joist return, and the coiled Ref.Piping is horiz. or parallel to the sheet metal panned joist ? If so, the Ref L/S design is probably OK, unless the line length becomes a question/issue. Note it, and comment that a Prof. HVAC Contr. should evaluate. I recommend that because you’re not a expert, and shouldn’t put yourself in the position of maybe being second guessed as overstepping your knowledge. Best for your client, and CYA for you, IMHO