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.

 

I thaught the circuit diagram was self explanetry on how to wire up just the compressor. The capacitor is the start cap.

 

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.

 

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

 

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.

 

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.

 

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.

 

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.

 

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.

 

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.

 

Hello debe, I have seen in another post of yours that you have a Koden MD-3000 repair manual. Can you send it to my email?

 

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.

 

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.

 

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

 

My mistake Rich2 you are quite right.

 

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.

 

At a first glance, it's not easy to see how the relays are energised, but substituting a couple of switches would see if it works.
Commercially, fridge compressors have been used as "silent" air compressors, Jumair was one make.
I used quite a lot of them, but they weren't reliable and eventually they all failed.
You'll need a pressure switch and as others have said, you might need an oil and water separator.
The receivers used were small, maybe about 10-litres and did need a drain cock on the bottom.
I concluded it was a nice idea, but not long term reliable. Mainly down to motor failure or water damage.
Eventually, all were replaced by conventional diaphragm or piston compressors

 

I have used a refrigeration compressor for inflating tires for many years. The first one lasted about 25 years, then it burned out, not sure why. The next one lasted only six months, the one after that lasted 2 years. My big problem is that every one is a different shape and size and so mounting them out of the way becomes tedious.
The solution to getting the start/run controls right is to not pull the compressor out of the assembly without the attached wiring. It is a small amount of extra effort but the result is always having all the needed pieces.