SIP compressor won't start? - Page 1
Forum section: electronics / repair

author: artv
author_rank: Contributor
timestamp: March 18, 2024, 07:20:57 am
content: HiMy 3HP SIP compressor won't start or make any attempt to start. There's no noise at all when I turn it on. It did come on a few times and then consequently trip the household electrics with a burning smell but I can't see where this burning occured.I've checked and there's 240V coming into the compressor. The thermal fuse checked ok. And both capacitors gave their currect reading.I've repaired the compressor a few times in the past but this has stumped me.Anyone have any ideas what might be wrong?Thanks!

author: Jeroen3
author_rank: Super Contributor
timestamp: March 18, 2024, 07:40:38 am
content: The poor thing lives outside... Is it mechanically jammed?

author: Zenith
author_rank: Frequent Contributor
timestamp: March 18, 2024, 09:36:12 am
content: Only a guess, but I'd say a motor winding with insulation that's broken down. Excessive damp is not something that makes for a long life with these things.

author: artv
author_rank: Contributor
timestamp: March 18, 2024, 09:57:58 am
content: Thanks.No it's not kept outside - it has its own little purpose built mini shed, attached to my workshop! But still gets damp in there no doubt where I live.I can turn the motor but it does seem stiff - not sure what it was like before though.If is windings woudl you say game over? Is there anything I can try before taking it to dump!I'm wondering if capacitors read ok and look ok - could they still be faulty? Also in my experience when these go, it would still try and start - but I'm getting nothing. Would that be right?Thanks.

author: Xena E
author_rank: Frequent Contributor
timestamp: March 18, 2024, 10:31:40 am
content: Is the pressure relief valve stuck shut?Is the start capacitor centrifugal switch stuck open?Start capacitor, (the big value one!) Going short under load?Valves stuck in the head?Is the auto full pressure switch stuck open? (Unlikely)Most of the above usually caused by disuse. Generic faults but I've no experience of that particular model.

author: Zenith
author_rank: Frequent Contributor
timestamp: March 18, 2024, 12:06:12 pm
content: Is the motor stiff when you try to turn it with no load attached? There could be an obstruction or the bearings have had it. The bearings should be standard parts.Do the windings smell and look burned?If it's the windings, a look on the web shows new compressors are about £500 and replacement motors are £300. There are rewinding services up and down the country, or maybe you could rewind it yourself.I don't think it's definitely the case that the windings are the problem and there are a lot of other possibilities to check out. It could be something basic like corroded contacts.

author: amyk
author_rank: Super Contributor
timestamp: March 19, 2024, 02:25:17 am
content: Open its output to the atmosphere so that you're not feeling the force of compression, and see if it's still difficult to turn. I recommend checking the cylinders for roughness.

author: Swainster
author_rank: Frequent Contributor
timestamp: March 19, 2024, 04:56:25 am
content: There is a suspicious mark by the overload switch. Speaking of overload switches, I had one fail on a cheap compressor - it's worth checking if yours is working properly

author: artv
author_rank: Contributor
timestamp: March 19, 2024, 08:43:51 am
content: Quote from: Swainster on March 19, 2024, 04:56:25 amYes the thermal switch did fail a while back and was replaced. This one is working though - I've getting 240V into the compressor. Thanks though.Quote from: amyk on March 19, 2024, 02:25:17 amI'm not quite sure what you mean here? Thanks.Quote from: Zenith on March 18, 2024, 12:06:12 pmThanks - do you mean extract the motor? I've not looked how easy it is to get to it. It won't be worth spending more than £50 on it.Quote from: Xena E on March 18, 2024, 10:31:40 amThanks - not exactly sure how to check some of those things but will take a look.

author: Zenith
author_rank: Frequent Contributor
timestamp: March 19, 2024, 01:37:45 pm
content: Quote from: artv on March 19, 2024, 08:43:51 amI'm not familiar with these things. I was thinking of unlinking the motor from the belt, in which case it should be possible to turn it easily by hand. Judging from the pictures the belt cover should come off easily and the belt probably has to be changed occasionally. Also it looks as if you should be able to look inside the motor and inspect it for obvious damage.If you just want a working compressor and really don't want to mess with it or spend anything much on it, why not look out for a second hand one of this or a similar sort? They can be quite cheap if they are collection only, and in that case you could see it work. Also spares can turn up.As I say, it might be something like a corroded contact.

author: amyk
author_rank: Super Contributor
timestamp: March 20, 2024, 12:16:14 am
content: Looks like a direct-drive compressor to me, with the motor and crankshaft in the same line.