fridge compressor to air compressor wiring problems - Page 1
Forum section: electronics / repair

author: capoman
author_rank: Contributor
timestamp: April 14, 2019, 08:19:27 pm
content: helloiv extract my old fridge compressor and and i want to turn it as an air compressorbut iv found dificulties to turn it on directly by mountin a switchi cant determin wich wire i will use to turn it on

author: hermit
author_rank: Frequent Contributor
timestamp: April 14, 2019, 09:27:12 pm
content: First, it will make a poor air compressor and will probably fail quickly when run open to air. Was there no schematic with the fridge? Can you find one online by using your model number?

author: james_s
author_rank: Super Contributor
timestamp: April 14, 2019, 09:38:01 pm
content: They work fine as light duty air compressors, my friend has been using one for close to 10 years now. You do need an unloader valve between the compressor and tank though as they will not start against a high head pressure, and some of them are prone to seizing if not run for an extended period.Most refrigerators have a PSC motor and there are 3 terminals on the motor. One is common which goes to neutral, one is live which goes through the thermal protector shown in the picture there to the motor, and the other connects through a run capacitor to live.

author: floobydust
author_rank: Super Contributor
timestamp: April 15, 2019, 12:18:47 am
content: Welcome to the forumCan you give us a make/model for the old fridge? It will help figuring out the wiring by looking at the old appliance's schematic.

author: PaulAm
author_rank: Frequent Contributor
timestamp: April 15, 2019, 12:51:01 am
content: In the last 10 years or so, most refrigerator compressors are run by an inverter. Before that they used a start relay and capacitor. Get the schematic and you should be able to figure out what you need.Some of the oil used is highly hygroscopic and it may be useful to drain it out and replace it with a similar quantity of normal vacuum or compressor oil.

author: shakalnokturn
author_rank: Super Contributor
timestamp: April 15, 2019, 07:11:35 am
content: When a start relay is used it's the (over) current of the stalled motor drawn on the run winding that triggers the relay to switch the start winding in.Some models use a PTC thermistor instead of a relay on the start winding. Looking at the photos I'm guessing it is the case here.A PTC will not allow the motor to start after a short stop, the PTC needs time to cool and return to a low enough resistance.

author: Electro Detective
author_rank: Super Contributor
timestamp: April 15, 2019, 09:59:16 am
content: I hope OP is wearing some personal protection, tight glasses/faceshield and gloves etcAir compressors and their fittings going -BANG!- don't care if you have family and friends that don't need the bad news

author: capoman
author_rank: Contributor
timestamp: April 15, 2019, 10:02:09 am
content: the fridge model its REX KBI 300and the compressore model its a ZEM r600athere is some pdfs on google of that ompressoreshowing the plugs .... but i dindt understand fridge schematics ....i dont know if i shoild use a capacitore as showen in some videos of converting fridge compressore to air compressor....thank you all for your answers

author: Electro Detective
author_rank: Super Contributor
timestamp: April 15, 2019, 10:25:47 am
content: @ capomanthere are many Youtube videos about DIY air compressors using fridge compressorsGood luck and play safe mate

author: Ian.M
author_rank: Super Contributor
timestamp: April 15, 2019, 11:20:55 am
content: Most small hermetic single phase refrigerator compressors use a start winding that creates the necessary phase shift by its high resistance relative to its inductance, without a capacitor, and due to the thin wire used for the start winding it will burn out if continuously powered, so will typically have a high current PTC thermistor in series with the winding to provide a crude time delay mechanism to cut (most of) the power to it after start. TThis prevents rapid re-starting as the PTC thermistor must cool first, but it stays hot as long as the motor is running. There's also normally a Klixon or similar over-temperature trip in series with the common to both windings, to provide some protection if for any reason the motor fails to start. Both the PTC and the Klixon are usually integrated in the connector that plugs onto the motor pins.If it didn't have a start or run cap don't add one!If you need rapid restart capability, the PTC needs to be able to cool down while the motor is running. Adding a time delay relay to cut start winding power is one approach, either in series with the PTC or replacing it.

author: Ian.M
author_rank: Super Contributor
timestamp: April 15, 2019, 12:28:45 pm
content: Confirmed. You can see the PTC thermistor (disk on edge between spring contacts at the top) and the disk face on,(bottom left) is probably the Klixon thermal trip. It looks like the start winding connector contact is the left top one, and the main winding contact is the right top one. The start winding contact wont go anywhere except the PTC, but the main winding contact goes to the PTC and one or more external connections. I'd also bet on the klixon contacts being in series with the bottom motor winding contact which should be the common.We had a thread about repurposing refridgeration compressors last year. Rather than re-hashing it, I'll point you to the comments I made in it:https://www.eevblog.com/forum/projects/air-brush-compressor/

author: capoman
author_rank: Contributor
timestamp: April 15, 2019, 01:47:20 pm
content: thank youbut i still dont know how to hook up the wires to make it work perfectly and saafe ?

author: Ian.M
author_rank: Super Contributor
timestamp: April 15, 2019, 02:12:23 pm
content: To make the compressor run, you need to power the main winding, with the start winding + its series PTC in parallel. If you link to the wiring diagram you found we can attempt to explain it, but there's no substitute for hands-on continuity and winding resistance checking to confirm your wire/terminal identification.Identify the two wires that go to the Klixon in series with the compressor's common pin, and that go to the main winding pin + to the PTC in the plug. Apply mains across them and it should start and run.Once you've got it to run, making it work as a usable air compressor is *LOT* more complex - see the thread I linked, but if you cant even get it to run, you are S.O.L. and cant proceed further.

author: soldar
author_rank: Super Contributor
timestamp: April 15, 2019, 03:51:33 pm
content: Always provide a pressure relief valve if you want to prevent explosions.

author: Ian.M
author_rank: Super Contributor
timestamp: April 15, 2019, 03:58:48 pm
content: Yes. In the old topic I also recommended adding a burst disk for a last resort final safety backstop in case of both pressure switch failure and safety valve clogging.

author: floobydust
author_rank: Super Contributor
timestamp: April 15, 2019, 06:08:39 pm
content: Quote from: capoman on April 15, 2019, 10:02:09 amI still don't have the compressor model number. ZEM is the manufacturer, r600a is the refrigerant.Fridge compressors need a capacitor (start or run) and so far it is missing from your pictures.

author: Ian.M
author_rank: Super Contributor
timestamp: April 15, 2019, 06:41:33 pm
content: Quote from: floobydust on April 15, 2019, 06:08:39 pmThat may be true of the 120V 60Hz compressors on the large fridges common in North America, but in the 220V-240V 50Hz rest of the world, small and medium domestic refrigerator and freezer compressors traditionally have used a thin wire start winding so its resistance dominates and provides the required phase difference relative to the inductive main winding, without a capacitor.See "Split Phase Motor" here:http://people.ucalgary.ca/~aknigh/electrical_machines/other/split_phase.html

author: soldar
author_rank: Super Contributor
timestamp: April 15, 2019, 07:24:39 pm
content: Googling for compressore zem gives dozens of hits including some youtube videos with explanations. You will find more info in Italian than in English.

author: floobydust
author_rank: Super Contributor
timestamp: April 15, 2019, 07:28:44 pm
content: Quote from: Ian.M on April 15, 2019, 06:41:33 pmI think this is what you are proposing, no start/run capacitor at all.

author: Ian.M
author_rank: Super Contributor
timestamp: April 15, 2019, 07:42:31 pm
content: Yes. That diagram has a split phase motor with the PTC starter in series with the start winding and the Klixon thermal trip in series with the common. You can see the PTC and the Klixon integrated in the push-on three pin motor connector in the photo in the O.P's reply #10, so its 99%+ certain that's what he's got.

author: capoman
author_rank: Contributor
timestamp: April 16, 2019, 10:59:59 am
content: Modell : ZEM HQM 12AA

author: capoman
author_rank: Contributor
timestamp: April 16, 2019, 04:17:10 pm
content: this its the board where the cables are connectedwhat if i try to start it normally without the ptc just with the 3 pins Comun Run Start

author: floobydust
author_rank: Super Contributor
timestamp: April 16, 2019, 07:28:19 pm
content: It's hard to figure out the wiring block. I can't see where the black wire goes, or the brown from the Klixon. That terminal blade seems top have no wire.My guess is to short black wire to brown wire (a to b), and leave the extra blue wire unconnected. Yellow-green is protective earth-ground.HQM 12 AA 2260050592 uses mineral oil 210cc, 12A start 1A run.

author: capoman
author_rank: Contributor
timestamp: April 16, 2019, 07:36:24 pm
content: iv tried to follow wires to make this simple diagramiv tried also to test the terminalsi hope i did the right setting on the multimeter :p

author: floobydust
author_rank: Super Contributor
timestamp: April 16, 2019, 08:33:46 pm
content: Move the brown wire over like this

author: capoman
author_rank: Contributor
timestamp: April 17, 2019, 02:47:29 pm
content: i already did but it did just a sparkin that case so the terminal A will be connected to the phaseand as we see the terminal B connected to the neutrwhat about the terminal C ?

author: capoman
author_rank: Contributor
timestamp: April 17, 2019, 04:23:33 pm
content: well iv tried your soulution it worked but it turn off after 30/40 secondand iv tried to turn it on with direct cablewitout relay .........but it have a low pressure u cant feel no air out

author: Ian.M
author_rank: Super Contributor
timestamp: April 17, 2019, 07:46:07 pm
content: Sounds like its FUBARed. Once started, a split-phase hermetic compressor should be able to run for hours unloaded (both intake and discharge pipes open to the atmosphere) without any signs of distress and produce more than 100 PSI operating into a reservoir with a pressure relief valve. It wont however start if there is a high back-pressure at the outlet.

author: capoman
author_rank: Contributor
timestamp: April 17, 2019, 08:37:02 pm
content: its a 1/5 hp i dont know that type of compresser if it produce air pressure or not ..... or its faultyi hooked ot up like that it start runing silently but no air

author: james_s
author_rank: Super Contributor
timestamp: April 17, 2019, 09:09:41 pm
content: Did it start or just hum? If the latter then it sounds like it's seized. Are you sure you have power going to the main winding and not the start winding? The start winding should only be energized momentarily.

author: capoman
author_rank: Contributor
timestamp: April 18, 2019, 06:45:24 pm
content: well i put the L to the comunN to the Runingand i did a push button between the R & Sguy is it realy dangerous if i mess with wirimgmy explod ?

author: PaulAm
author_rank: Frequent Contributor
timestamp: April 18, 2019, 08:12:37 pm
content: These compressors really don't have a lot of start up torque. When they start up inlet and outlet pressures are the same so there's no initial load. It's possible the bearings have gummed up in which case it's toast.I had a new compressor die after an hour so I opened it up. That one had a faulty oil path so the bearings had gummed up. It's amazing how little is in there.

author: floobydust
author_rank: Super Contributor
timestamp: April 18, 2019, 08:33:50 pm
content: capoman, what was wrong with using the factory terminal block?It has the thermal overload Klixon and PTC for starting. Make sure the compressor has a ground wire. If the motor is burnt it will short-circuit Line to case and you will get electrocuted. Be safe.When it ran for 30-40 seconds, either the Klixon tripped from overheating or the motor has no oil and seized. The datasheet says mineral oil 210cc.

author: amyk
author_rank: Super Contributor
timestamp: April 19, 2019, 02:13:17 am
content: It'll be very,veryobvious if it's actually running, because it'll be sucking and blowing...here's a good video to watch about how to connect these:

author: capoman
author_rank: Contributor
timestamp: April 19, 2019, 05:25:53 pm
content: |Owell if i use the ptc / klixonthe compressor start for a while 20s / 30 s then shut off

author: james_s
author_rank: Super Contributor
timestamp: April 19, 2019, 06:29:10 pm
content: That's a great idea hitting a seized compressor with 240V momentarily to free it up. I had a rotary compressor I was using as a vacuum pump that seized up after sitting and I ended up chucking it up in a lathe, spinning the whole compressor up to speed and then stomping on the brake treadle. It did work, but was only feasible with the rotary compressor which was both round and had the internals rigidly mounted. Reciprocating refrigeration compressors sit on springs inside the dome.