Hi there,

Last year while on a long overlanding trip my air compressor died. Not having any experience with electronics I wasn't able to fix it but now I've taught myself a little electronics and would like to try and repair the compressor which is powered via a 12V car battery. I've taken it apart and so far my best guess is that there is a problem with either the relay or something that I assume is a pressure switch (photographs attached) or possibly both. I'm betting it is the relay as there appears to be some heat damage on the circuit board. Of course I have no idea if it is the motor or anything else but I've had a close look at all the parts and can't see anything that would indicate damage. The switch isn't a problem as I've already tested it with a multimeter.

This is the exact same relay: https://m.aliexpress.com/item/32726635296.html in the compressor but I cannot find the datasheet online. This would appear to be the closest I can find that is available locally for a replacement should that be the issue: http://www.communica.co.za/Content/Catalog/Documents/D0490228122.pdf

WH-101 50A 125/250VAC is printed on the box that I assume is a pressure switch but it doesn't mean much to me.

Is there anyone out there who would be able to give me some ideas of where to get started with trying to repair this compressor?

Thank you!

 

Ok Not sure what it is your asking?

Here is a question. What happens if you take Pin 30 off and Pin 87 off, Then use something heavy gauge and jump them *Not on the RElay* I am saying put the 2 wires you took off together plug in the pump or turn it on does it work at that point?

In case you don't know.. Pins 86 and 85 are control to make switch on or off. 30 and 87 is contacts that would be complete when switch is energized... I am not saying to bypass it for good. I am saying you can bypass for a moment to see if pump works again...

James

 

I have never seen a 12V compressor that would run for more than 10 minutes without seizing up.
Cheap compressor is cheap.

 

I am not sure I agree with the 10 min, chuck it away comment but I will agree there is some possibility it simply failed mechanically.

However, given that you are learning I would suggest you start by drawing the circuit.

I apriciate you cont know what at least one of the parts is but knowing where and how it is connected will give you a clue to its function.
If it is a pressure switch it will be connected, by a port, to the compressors high pressure output.

I dont mean any offence but diagnosing this sort of thing is relativly simple and the fact that you are asking for help indicate a willingness to learn, which is a good thing.
IT may seem like overkill to many to draw this basic circuit out but you will learn a great deal about thew diagnostic methodology you need to employ to any simmilar task.

The fact that you have a great deal to learn is not a failing, it is an opertunity....

Once the circuit is drawn you can make some assumptions and then test them.
This will ultimately tell you which part has failed and ultimately what you need tom do about it.

What test equipment do you have? you will need a cheap multimeter at the very least to do a proper diagnostic, but a simple test lamp/probe may be enough to find the bad componant.

I would be inclined to suggest that mending the compressor is actually less significant than what you can learn doing it.

Happy to help if I am around when you ask questions.

Al

 

I am not sure I agree with the 10 min, chuck it away comment

I only meant that post #2 recommending a direct connection to power will probably reveal a seized up compressor.
If that isn't true, go for post #4.

 

Thank you for your feedback!

IMP002017 - thank you for this I will give it a shot!

#12 - this is not exactly a cheap compressor. It's done me good service over a range of different conditions and has taken quite a bit of abuse. It just died one day - it happens I guess.

Dyslexicbloke - thank you for your response. I didn't have enough information and actually now know that the "pressure switch" is actually a circuit breaker so I imagine the only problem can be the relay (but it could be an entirely mechanical issue) so as you suggested I've drawn out the circuit which I've attached. So what I plan to do to test the motor is to remove the circuit breaker and the relay and just wire the motor straight to the battery as shown in the second schematic that follows the first.

I've also attached some images of the battery connections to the motor and as you can see the blue wire there is probably redundant so I'll be removing that to simplify my circuit. Once I can confirm that the compressor is again working then I'll try and source a new relay and then wire the circuit back to the original spec.

Does that seem reasonable?

Thank you!

 

I would recheck your drawing. Something there not making sense to me. Where is terminal 86? Somehow you need to energize the coil to make the switch work.
If the motor does not work, check the thermal limiter under that piece of shrink tubing. Common part to fail.

 

I would recheck your drawing. Something there not making sense to me. Where is terminal 86? Somehow you need to energize the coil to make the switch work.
If the motor does not work, check the thermal limiter under that piece of shrink tubing. Common part to fail.

Hi there thank you for your response and sorry for my late reply, for some reason this website wasn't loading? Anyway, terminal 86 was not connected to anything.

 

Well then you may want to find out where the connector for 86 is. This relay needs to have ground and + voltage make the switch activate. If it don't then pins 87 and 30 can not close to make Switch contact.

Did you do as I was saying and take 87 and 30 off to make contact to test that pump turns on?

 

Well then you may want to find out where the connector for 86 is. This relay needs to have ground and + voltage make the switch activate. If it don't then pins 87 and 30 can not close to make Switch contact.

Did you do as I was saying and take 87 and 30 off to make contact to test that pump turns on?

Thank you for your reply. There was nothing soldered to terminal 86 - I've attached a photo.

I haven't tested it yet, no.

 

Compressor is connected to the battery by two alligator leads (red and black):

Red lead (positive) goes into the circuit breaker.
Circuit breaker output goes into terminal 87 of the relay.
Terminal 30 of the relay goes into one of the motor brushes.
Terminal 85 of the relay goes into one of the switch pins while the other pin is connected to the motor.
Black lead (ground) goes into the other motor brush.

All of this is illustrated in my circuit diagram which is attached.

There is no connection to terminal 86 of the relay which seems fine to me as my understanding is that only one of those terminals is necessary for the closing the switch between 30 and 87?

Thanks!

 

According to the schematic on the relay, the coil needs power and ground to activate 30 and 87. With no connection on 86, I do not see how it would work. Another option would be that terminal 30 and 86 are tied together internally somehow, but that is not the indication on the relay. Take an ohmmeter and test for continuity between 30 and 86 and let us know what you find.

 

Well your Diagram is lacking....

30 and 87 have no connection without 85 and 86 making a contact....

So in your diagram it would be an OPEN Circuit... that is why it don't work...

Only 2 points in a Relay that can pass ground or + that is 86 and 85 because it is a Coil. However in your Diagram it shows in that Relay being an OPEN Circuit...

Edit: without power being applied. 86 and 85 could pass though, Unless it was a 5 pin and then it would have a 87a pin and that would pass to 30 without power. that is the rest of my thought on 2 points on a relay that can pass though...

James

 

According to the schematic on the relay, the coil needs power and ground to activate 30 and 87. With no connection on 86, I do not see how it would work. Another option would be that terminal 30 and 86 are tied together internally somehow, but that is not the indication on the relay. Take an ohmmeter and test for continuity between 30 and 86 and let us know what you find.

The only continuity seems to be between 86 and 87. I've tried all combinations... Definitely nothing between 30 and 86.

 

There is something very mysterious about this whole thing. In order for you to create an electromagnet, this relay should need power and ground provided to the coil (terminals 86 and 85) When the electromagnet is energized, current should then flow from terminal 30 to 87 as the switch closes and then on to the load device. 86 and 87 should never come together. That still doesn't explain where the wire for 86 is? Has this been rewired?

 

Hi IMP002017 and bwilliams60 - I've taken two photographs of the relay (which I have cut off) and you can see there are only three wires that were soldered to the relay terminals (I hope the photos are clear enough).

There's no way a fourth wire somehow fell off when I opened up the compressor. That is what I saw in there?

It defintely hasn't been rewired. I bought the compressor and I know for a fact that it worked and no one touched it until it died and I was the only one to open it up.

 

You mentioned in post 6 that you have a blue wire that is redundant. Why is that? Was it hanging around? There is solder on terminal 86 which would indicate to me that something was connected to it. What make and model is this compressor. It seems so simple. I know how I would connect it but something is amiss here I am afraid.

 

Ok then there is a way to do it with 3 wires but clearly there is 4 spots for the wires....

So there has to be one wire that is used as Ground that is connected to pin say 85 and 30. or it could be a Positive that goes there either way there has to be something missing to make this 4 pin Relay work...

 

Looking at your Diagram. I see there is a ground at the Motor. When you close the Switch between the motor and the relay it should turn on the motor. Pin 87 also goes to Pin 86 if that was the case this would work in the way a relay works....

James
So I would tie pin 87 to pin 86 and with the switch see what happens...

 

wait I see in the picture you provide it is a Mini PCB and there are only 3 wires because it is connected via the PCB that is why there is only 3 wires on this....