Jun-Air model 6 will start once?

by Sam
(Regensburg, Bavaria)

Jun Air Model 6-25 (Photo: www.jun-air.dk)

Jun Air Model 6-25 (Photo: www.jun-air.dk)

Hi Bill,

Jun-Air model 6 will start once, but has trouble after the first cold start and fill

I have an old model 6 from 1980 that I got from a friend. I have been using it for the last few months without issue, my usage is that it compresses to 8 bar and this is slowly bled out over about 15 minutes down to 6 bar where the switch then kicks it back on and fills it back out to 8 bar.

Recently, I noted that it is not kicking in anymore at 6 bar and will only start filling again around 3 or 4 bar. That is when I discovered that it is trying to kick in at 6 bar as it should, but the motor rotates only once or so and it stops again, it does this several times, each time there is a little jiggle of the unit, but it doesn't start like it should, it just keeps clicking on and off irregularly (not a constant clicking, just once every thirty seconds or so).

When I leave it for a few hours and then start it again, it starts right off and fills straight to 8 bar.

It also seems that it is generating more heat than it used to when it is doing this on and off, but that may be subjective on my part.

Oil is full and the inlet filter has no effect on the behaviour.

I am inclined to think it is either something wrong with the motor, or capacitor, or the pressure switch, but I didn't see any change in behaviour when I had the cover off and was moving the set screws around. I don't think it is a thermal issue because it does the same thing after the initial fill and at that time it is still relatively cold.

Any ideas?

A couple if ideas, Sam.

One is that the compressor tank check valve is leaking a bit, and that's allowing the tank air to bleed out to atmosphere and bringing the tank pressure down to cut in.

With the tank empty and the compressor off, remove the line from the pump to the tank, disassemble and clean the check valve, and reassemble and test the compressor. If the cleaning removes the leak good. If it doesn't, then you may need a new check valve.

As to the restart issues, pop on over to the troubleshooting section on the site map page, and follow the links to unloader valve issues. If the unloader isn't working properly, that could account for the inability of the compressor to start under pressure.

Post any developments here, if you would.



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Dec 29, 2012
compressor did not work properly
by: angelo

hi bill
the problem is when the compressor start to run it have a 15.5 ampere then the overload cut it off,i try to replace the push on type relay,starting capacitor and overload relay but nothings happen..can you pls. help me fix it the brand is Jun air compressor and the running current is only 2.9ampere..tnx
Angelo, before you try to start it again, dump all the air out of the tank. Then see if it starts and runs up to cut out. If it does start, make sure the unloader valve works when the compressor stops. If it does not, then I believe your Jun Air compressor is trying to start under too much load.

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Jun Air Model 6m question

by Glenn

May i know the specification of jun air 6m, 14 bar, how many horse power?

Is it silent type? and how does it work at witschi alc 2000?

Bill answers...

Hi Glenn:

The 6 model series of Jun Air compressors were all the "silent" type, all of them generating a maximum of 45 dB.

All were, I believe, oil lubricated.

They manufactured them with a .54 HP and a .46 HP motor.

And, I'm afraid, I don't know what this ... "how does it work at witschi alc 2000 ..." means.

Here is where I found the spec sheet.



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