I bought a new split AC that worked great for a week or so, but now I can hear some annoying noise coming from the outdoor unit. The outdoor unit in installed on a flat roof so I can hear this noise even when I'm inside the room. (Noise sample), is this normal?

Another things I noticed is that the the AC pipe gets wet when it's running, is this normal ? (Video).

  • The suction line will get wet when it's running. It's cold, so moisture from the air around it is condensing on it. No problem there.
    – Tester101
    Commented Jul 20, 2015 at 12:22
  • 1
    Have you contacted the company that installed the unit? They likely have some form of warranty or satisfaction guarantee, and would be willing to at least come take a look.
    – Tester101
    Commented Jul 20, 2015 at 13:36
  • I didn't contact the company that installed the unit yet, I just wanted to know if this is normal or not. You didn't answer my first question about the compressor noise, it passes through my roof into my room and I can hear it, is this the normal compressor sound and I should just install anti-vibration pads below the compressor or it's a faulty compressor ?
    – donald
    Commented Jul 20, 2015 at 15:05
  • I didn't answer either of your questions, I simply commented on why an A/C pipe would be wet.
    – Tester101
    Commented Jul 20, 2015 at 16:13

1 Answer 1


The compressor noise in your video is not normal.

Some of the possibilities for this noise are:

  1. Non-Condensables

    Things that can't condense, such as moisture, ambient air, etc. can make a compressor chatter like that because it is trying to compress something that doesn't want to compress.

    Ask an HVAC Technician to recover, evacuate, and recharge your unit to eliminate the chances of non-condensables being present in the system. Refrigerant filter installation would also help.

  2. Compressor Bearings

    Sometimes compressors aren't pre-charged with oil from the factory. That could an oversight on the manufacturer, or the contractor that did the installation. Most mini-splits however do come pre-charged with oil. What could also be a problem, is oil from your compressor has pumped itself throughout the system, and hasn't been able to return to the compressor.

    This can be eliminated depending on how the line set is installed. Creating oil-traps is typically the best way to go - it prevents the oil from leaving the compressor. But there should only be one oil trap close to the unit in the line set. Additional traps throughout the system will trap oil and prevent it from going back into the system.

    Oil is integral for keeping the bearings lubricated and from overheating. Friction will warp the bearings, and cause the spin of the compressor to make loud noises.

  3. Non-Level Installation

    If the outdoor unit is not installed level, then the compressor could be spinning on an uneven axis. This could also create noise, and will eventually warp bearings (if it is a compressor that has them) which creates even more noise.

  4. High Amperage

    Check the amperage of the power going into the compressor - not the entire unit. Make sure that it matches its amp rating. If it is too high, then it can start making noise because a by-product of electricity is heat. Heat causes metal expansion internally and can increase friction of delicate parts within the compressor - creating noise - warping bearings - etc.

The moisture on your line set is normal.

As was mentioned in comments, this is natural. In the HVAC industry, we call it "sweat back." Meaning, you have heat transfer happening - it's doing its job. This is no different than setting a cold can of Coke onto the table, and seeing the condensation build up on the outside of the can.


If you don't like to see the drips, then installing more insulation (Armor Flex is a common term) on your line set will help a lot. Some technicians will even try to cover the service ports. Moisture will attract dirt. Dirt is an inconvenience on the service ports and if not removed prior to hooking up manifold gauges, can clog the gauges themselves.

Something else to consider is Slim Duct or SpeediChannel (those are brand names) but it protects your entire line set from the environment (and other mischievous creatures such as rodents and people). Here is an example:


It also has an aesthetic quality - it looks better on the outside of your home and can even be painted to match the color of your home.

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