the snooper
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surley if start cap wasnt in circuit the motor wouldnt start at all and it would just buzz like a failed cap
- Thread starter alfapat
- Start date
In majority of cases thats true especially with cap start induction run, but with a start and run cap motor the start winding is in circuit all the time and it could start sometimes against no load, but if the start cap through the centrifugal switch is not dropping out as it should it would trip the over-current device.
the snooper
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the centrifugal switch must be dropping out as its only a start issue, once running its ok the problem is it doesnt start so the start circuit is in too long causing it to draw the start current for too long then tripping out via the thermal cut out
Don't know if I'm reading your last post correctly, but you say the centrifugal switch must be dropping out in the first part of your reply, but then in what appears to be a bit of a contradiction you say the start circuit is held in too long which could mean the centrifugal switch is not dropping out, causing an overcurrent trip, which might suggest that maybe there could be a problem with the start circuit side of things, assuming its an electrical fault that is and not a pressure unloading fault. But whats clear enough though is that its a starting problem.
the snooper
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no once the motor is running the centifugal switch must be opperating correctly as it doesnt trip.
but when cold and the comp doesnt start the motor doesnt get up to speed so the start circuit will stay engaged until it trips as it cant spin fast enough to disengage it
but when cold and the comp doesnt start the motor doesnt get up to speed so the start circuit will stay engaged until it trips as it cant spin fast enough to disengage it
Cret
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That's an interesting theory, but I suspect if that was the cause it would surely startup fine but subsequently cut out, or at least cut out while appearing to be going through a good startup process?
Reason I say that is if the circuit was used too long and all else was fine, I'd expect (guess) the motor would get up to speed happily enough, or appear to be doing so, but the dodgy circuit would then trip the cut out regardless of whether it started ok or not.
Whereas what actually happens is that the motor appears slow to turn initially, and with a good start/empty tank it then speeds up properly and runs fine, but with a bad start it seems to slow rather than speed up after its initial rotation begins.
That's sort of the reason why I was suggesting that while the caps themselves must be ok, that perhaps the power from the start cap is not reaching the motor to give it that initial kick.
To test this, if I simply remove a wire from the start cap and try to run the compresspr would it still function (in the sense that it would actually try to start without the benefit of the cap), or would the removed wire cause an open circuit where nothing works?
If that's a test that would work then it would at least confirm if there is a difference in the behaviour between the start cap being connected or disconnected. If there's no difference when disconnected (ie still starts on empty but not with tank pressure) then wouldn't that indicate that while the cap itself is ok it's just not getting its juice through to the motor?
Reason I say that is if the circuit was used too long and all else was fine, I'd expect (guess) the motor would get up to speed happily enough, or appear to be doing so, but the dodgy circuit would then trip the cut out regardless of whether it started ok or not.
Whereas what actually happens is that the motor appears slow to turn initially, and with a good start/empty tank it then speeds up properly and runs fine, but with a bad start it seems to slow rather than speed up after its initial rotation begins.
That's sort of the reason why I was suggesting that while the caps themselves must be ok, that perhaps the power from the start cap is not reaching the motor to give it that initial kick.
To test this, if I simply remove a wire from the start cap and try to run the compresspr would it still function (in the sense that it would actually try to start without the benefit of the cap), or would the removed wire cause an open circuit where nothing works?
If that's a test that would work then it would at least confirm if there is a difference in the behaviour between the start cap being connected or disconnected. If there's no difference when disconnected (ie still starts on empty but not with tank pressure) then wouldn't that indicate that while the cap itself is ok it's just not getting its juice through to the motor?
the snooper
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if you remove the start cap it will only buzz it wont even attempt to turn
Cret
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Happy to try but I have to admit I'm not savvy with the details of precisely how I go about that.
Shouldn't the run cap be ok since I replaced it, or do you mean that its power is getting through to the motor?
I did take the rear cover of the motor off last week but wasn't sure of how to proceed from there since it transpired just to be a fan cover with this beneath:
Shouldn't the run cap be ok since I replaced it, or do you mean that its power is getting through to the motor?
I did take the rear cover of the motor off last week but wasn't sure of how to proceed from there since it transpired just to be a fan cover with this beneath:
rtbcomp
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Just to clarify.
The valve in the pressure switch has 2 functions.
1) to empty the delivery tube when the motor switches off.
2) to bleed air from the delivery tube until the pressure reaches 20 psi.
To expand on point 2. Some types of valve close immediately, these are for low volume compressors (like fridge motors) or where a separate valve is used. The one fitted to your compressor will be the delayed type.
Snooper's suggestion of fitting a 2nd delay valve in the intercooler means that with two valves bleeding air out it will take longer for the pressure to build up, thus increasing the chances of the motor reaching speed before it comes under load.
The valve in the pressure switch has 2 functions.
1) to empty the delivery tube when the motor switches off.
2) to bleed air from the delivery tube until the pressure reaches 20 psi.
To expand on point 2. Some types of valve close immediately, these are for low volume compressors (like fridge motors) or where a separate valve is used. The one fitted to your compressor will be the delayed type.
Snooper's suggestion of fitting a 2nd delay valve in the intercooler means that with two valves bleeding air out it will take longer for the pressure to build up, thus increasing the chances of the motor reaching speed before it comes under load.
Cret
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Ahh I see - I couldn't quite grasp why it would behave any different to the current one, but that's not the case, it's just that two of them combined will cause it to double up (or whatever) the time before the pressure reaches 20psi.
In theory that's fine but I honestly think in practise and from experience of what the motor is like when it "doesn't want to" start, I still don't think it'd be enough.
In theory that's fine but I honestly think in practise and from experience of what the motor is like when it "doesn't want to" start, I still don't think it'd be enough.
Cret
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Spoke to them just now and they've basically said I've already gone beyond all the things they would have been testing themselves with a returned unit, and that at this stage (having replaced a few of the other parts likely to be at fault) they would be sending the motor back to the manufacturer (inc cap box) for a replacement motor to be sent out.
So I need to speak to the seller and arrange this with them.
I hope once that's done it'll be the end of all the problems but I've almost lost faith in this thing!!
So I need to speak to the seller and arrange this with them.
I hope once that's done it'll be the end of all the problems but I've almost lost faith in this thing!!
A few tests for you with your new clamp meter.
Select volts and test the incoming voltage at the motor (I know you've done this already but lets do it again just for the hell of it) write it down.
Then test the voltage on the run cap,the white one (put your probes between the connector that you have the one maroon wire and the other terminal that has the two black wires, make sure that the volts are on 400 or higher) Write that reading down.
Then change the meter to amps and check the amp draw through the run cap, clamp around the single maroon wire, write that reading down.
Switch motor off.
Now with your clamp meter still on amps, clamp round the red wire thats on the start capacitor, then switch on.
You should get a reading and then if the centrifugal switch is working it will drop off to nothing.
Select volts and test the incoming voltage at the motor (I know you've done this already but lets do it again just for the hell of it) write it down.
Then test the voltage on the run cap,the white one (put your probes between the connector that you have the one maroon wire and the other terminal that has the two black wires, make sure that the volts are on 400 or higher) Write that reading down.
Then change the meter to amps and check the amp draw through the run cap, clamp around the single maroon wire, write that reading down.
Switch motor off.
Now with your clamp meter still on amps, clamp round the red wire thats on the start capacitor, then switch on.
You should get a reading and then if the centrifugal switch is working it will drop off to nothing.
Cret
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Thanks for the info eil - appreciate the instructions.
After speaking to the nice people at Sealey tech and Proparts in Peterborough where I bought the compressor, they're sorting out the motor replacement for me (including capacitor box etc), so all I need to do is remove and box it and they'll arrange for a courier to collect it, and for a replacement to be delivered.
Hopefully this will solve the issue once and for all but I've thought that previously admittedly.......
I should try to do these tests anyway though to possibly satisfy my own curiosity and to see if I can identify a fault still.
One other issue is they want the motor back without the pulley. I think from memory it has no nut on the motor shaft, so does the pulley just tap loose gently or do I need a proper puller to remove. Can't recall if it has a woodruff key or anything like that.
After speaking to the nice people at Sealey tech and Proparts in Peterborough where I bought the compressor, they're sorting out the motor replacement for me (including capacitor box etc), so all I need to do is remove and box it and they'll arrange for a courier to collect it, and for a replacement to be delivered.
Hopefully this will solve the issue once and for all but I've thought that previously admittedly.......
I should try to do these tests anyway though to possibly satisfy my own curiosity and to see if I can identify a fault still.
One other issue is they want the motor back without the pulley. I think from memory it has no nut on the motor shaft, so does the pulley just tap loose gently or do I need a proper puller to remove. Can't recall if it has a woodruff key or anything like that.
rtbcomp
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It could also have a grub screw, either pressing against a flat machined in the shaft, or against a Woodruff key or a straight key.
Have a look down the end of the pulley to see if there's a keyway.
Once you've undone any screws you may need to warm the pulley and use an extractor to pull it off. The technique is to put the puller in place, tighten the screw using a normal spanner and then give the end of the puller screw a sharp tap with a hammer, repeat until the pulley comes free, tightening the screw as you go. Drifting the pulley could damage the pulley or the motor bearings.
Be very careful, it's easy to break an aluminium pulley by overtightening the puller.
Have a look down the end of the pulley to see if there's a keyway.
Once you've undone any screws you may need to warm the pulley and use an extractor to pull it off. The technique is to put the puller in place, tighten the screw using a normal spanner and then give the end of the puller screw a sharp tap with a hammer, repeat until the pulley comes free, tightening the screw as you go. Drifting the pulley could damage the pulley or the motor bearings.
Be very careful, it's easy to break an aluminium pulley by overtightening the puller.
