Turning Dehumidifier Compressor into Air Pump, Wiring Issues

Thread Starter

electronicnoob101

Joined Dec 16, 2020
2
Hi all,

So I've disassembled an old dehumidifier and want to turn the compressor into an air pump/compressor. The problem I currently have is trying to get the compressor to kick on. With the wiring configuration shown below, I have plugged it into an outlet and hear an audible beep from the humidity sensor (I think) but cannot get the compressor to run. I was wondering a few things if anyone is willing/able to help: First, is the wiring correct - the tan line coming from the left is from the outlet and the black line going to the top is to the compressor. The wiring diagram mentions a motor which I think is to a fan that I dont need. Second, if the wiring is correct is there a way to bypass the circuit board and only deal with the capacitor so there is no need to 'trick' the system into thinking the compressor needs to run. Lastly, if it is necessary to make the unit think it needs the compressor to run, how might I go about doing that? Thanks in advance for any help or ideas anyone can offer.
 

Attachments

debe

Joined Sep 21, 2010
1,214
I thaught the circuit diagram was self explanetry on how to wire up just the compressor. The capacitor is the start cap.Wiring Diagram.jpg
 

debe

Joined Sep 21, 2010
1,214
If you are going to use it as an air compressor you will need an oil seperator on the pressure line. AC & Fridge compressors tend to circulate oil in there systems. And they are capable of quite high pressures but not a lot of capacity.
 

Thread Starter

electronicnoob101

Joined Dec 16, 2020
2
If you are going to use it as an air compressor you will need an oil seperator on the pressure line. AC & Fridge compressors tend to circulate oil in there systems. And they are capable of quite high pressures but not a lot of capacity.
Thanks for the reply, I will look into getting an oil separator. As for the wiring, this is about the first diagram Ive ever looked at so while it seems simple enough Im hesitant to try anything. It seems to me that putting the mains active on the capacitor where the brown wire connected to CN-AC1 on the board would work, maybe Im wrong though. Thanks again for your time and consideration
 

Rich2

Joined Mar 3, 2014
175
That capacitor is a permanent run capacitor on the start winding. Doesn't look like there is a start relay, so there is no start capacitor.. Just put a live onto the OLP (overload protector) and neutral onto the run winding. As long as the capacitor is left in circuit it should start OK.
 

scorbin1

Joined Dec 24, 2019
55
If you put Line to the brown wire you will be creating a direct short. Line should connect to Black, (definitely keep the OL protection) and the Neutral to Brown. RY-COMP inside the box is simply a relay to turn the compressor on and off. I would recommend keeping the relay and using it for control in whatever you are creating.
 

scorbin1

Joined Dec 24, 2019
55
That capacitor is a permanent run capacitor on the start winding. Doesn't look like there is a start relay, so there is no start capacitor.. Just put a live onto the OLP (overload protector) and neutral onto the run winding. As long as the capacitor is left in circuit it should start OK.
I would lean toward disagreeing with you there. Not likely to need a run cap but compressors sometimes have to overcome extreme pressures to get started, hence a start cap is almost always necessary. The centrifugal switch would be internal to the motor and is likely just not indicated on the diagram.
 

Rich2

Joined Mar 3, 2014
175
I would lean toward disagreeing with you there. Not likely to need a run cap but compressors sometimes have to overcome extreme pressures to get started, hence a start cap is almost always necessary. The centrifugal switch would be internal to the motor and is likely just not indicated on the diagram.
If it is a capillary system the head pressure and back pressure soon equalises so high starting torque compressors aren't always needed. Bigger systems with thermostatic expansion valves don't equalise as well and need at least start relays and very often start capacitors too.
The three start relay types I've come across in refrigeration compressors are PTC, current relay and potential relay (hard start kit). Never seen a centrifugal relay although I think some old fans used them.
 

Tonyr1084

Joined Sep 24, 2015
5,515
Two important things: First is how much pressure you can build. If your air tank (lets ignore the oil issue for now but) if your air tank can not hold all the pressure the pump can create - you're going to have a 500 horse power rocket motor flying around in your room, garage or wherever it happens to let go. Very dangerous. People have done it - but it's dangerous. That's why you see it on YouTube. Sometimes I call it "Boob Tube" because I see a lot of things posted by boobs.

Second thing, they are very very very slow at building pressure. To get a four gallon tank up to 100 PSI can take an hour. And a four gallon tank isn't much air reserve. If you want a compressor then buy a UL approved compressor with tank. They've already done the engineering and safety calculations for you.
 

debe

Joined Sep 21, 2010
1,214
Been away from internet for a few days. This is the actual circuit of the compressor & the capacitor is the start capacitor. If you intend to pump up a air tank put a pressure relief valve adjusted to the safe working pressure. Be aware a refrigeration compressor may not be a lot of capacity, but i have seen them pump 250 PSI if they are in ressonable condition.Al.jpg
 

debe

Joined Sep 21, 2010
1,214
I can try, but the last time i tried to send by email it would not work as too mutch Data. Had to send it on a Disc. Go to KODEN MD-300 thread have posted some info there.
 
Last edited:

MisterBill2

Joined Jan 23, 2018
7,697
The circuit shown in post #10 will work, and you absolutely need that capacitor connected as shown. But you also need a pressure cutoff switch. I have done exactly that same arrangement for a portable pressure source several times and they work well.
 

Rich2

Joined Mar 3, 2014
175
Been away from internet for a few days. This is the actual circuit of the compressor & the capacitor is the start capacitor. If you intend to pump up a air tank put a pressure relief valve adjusted to the safe working pressure. Be aware a refrigeration compressor may not be a lot of capacity, but i have seen them pump 250 PSI if they are in ressonable condition.View attachment 225318
That's a run capacitor. Google it if you want ;)
 

MisterBill2

Joined Jan 23, 2018
7,697
Refrigeration compressors do have a lower flow rate and so you would need an air tank to be able to get an air flow adequate for many applications. But they can be useful if the high delivery flow is not needed.
 
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