Whistling or screaming sound when an old package unit is running.

579 Views 5 Replies 3 Participants Last post by dj3, Jun 26, 2020

justplumducky

Discussion Starter · Jun 21, 2020

What causes a whistling or screaming sound when an old package unit is running. Sounds like it’s coming from inside the evaporator coil and/or the compressor area. The first time I heard this was when the unit was shutting down. I’ve heard this kind of noise before when an old pkg unit was shutting down, and it made me think it was something like refrigerant moving… bleeding off pressure? First time I heard it on this job, it seemed abnormally louder then I remember hearing it once or twice on previous jobs.

On the same job after the unit was running for a while the noise repeated while it was running (not after turning it OFF), and it was extremely loud this time... I shut it down and left it that way. Told the owner not to run it and I would get help/advice and get back.

Just googled about the this noise and the first result to come up was about it being dangerously high pressure at the compressor, but it was regarding an automotive air-conditioning system.

Didn‘t connect gauges yet, and beginning to wonder if I should just stay away from it.

I have a bit more to tell about the condenser fan not running for who knows how long, but started running after replacing the dual run cap that tested well below tolerance for the FAN.
When first walking up to this unit, fan wasn’t moving and was making a strange noise in addition to typical humming, and I’m beginning to wonder if that strange noise wasn’t coming from the compressor. I could move the fan blade only a little with a screwdriver, but it didn’t bounce back like I’ve seen before when a condenser fan motor would lock up when the system was energized, and was told this locking up while energized was due to winding insulation having worn off and setting up opposing electromagnetic fields... power off and fan moves again normally.

Sent from my iPhone

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justplumducky

Discussion Starter · #3 · Jun 22, 2020 (Edited)

beenthere said:
Without hearing the noise, can't begin to make a reasonable guess.

If you could be sure it's not a FAN motor or blower motor noise, but a sort of hollow-sounding/gurgling-type noise not long after unit is shut off (the noise gradually reduces in intensity), and assuming it couldn't be anything but refrigerant pressure changing-related, could you offer any possibilities then? If not, I'll just have to run it, and this time note (on paper) exactly what happens (in sequence) etc., record the noise and get back.

As long as the unit is buttoned up, and I keep my distance should the compressor plug blow (its name escapes me at the moment), I'll assume I would probably be OK. No longer have the "partner" that was helping me when needed, but working on getting another experienced tech to look at this unit.

I should clarify that the noise I'm talking about now in this post relates only to my aforementioned experience (post #1) with this noise a couple of times (old MH pkg units), but wasn't loud like when it happened during running of the unit, before it shut down. Then it was a scary loud prompting me to immediately to shut it down, but if it's truly a pressure bleeding OFF/a combined hissing (internally)/gurgling-type noise, reducing in intensity as unit shuts down, I reckon it could be worse regarding safety while working on it.... or not, and I understand you have to be careful with your advice. However, the noise when it happened during running of the unit (scary loud then), is indeed the same type not loud noise described above when shutting down, just more intense when it was running.

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justplumducky

Discussion Starter · #5 · Jun 26, 2020

beenthere said:
Put gauges on and see if they tell you its the internal relief valve.

An HVAC company came out and condemned the unit, thx.

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