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Oilless Compressor OF45150A Problem

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  • Oilless Compressor OF45150A Problem

    I've had this compressor since new in 2006. It gets occasional use inflating tires, and nailers. Sits in my unheated garage year round.

    This spring it started acting up. When started it will fill the main tank to 150psi which is the max. All good. When it gets to 150 it lets air out till 120 and holds at 120. If I use that air it will refuse to turn back on. It will deplete all 120 psi and the motor will not come back on to repressurize the tank. Turning it on and off has no effect on this behavior. Sometime it will hum as if the motor wants to start but it cant. If I unplug it, wait a minute or two - it will repeat this process - back to 150 then release air to 120 then refuse to refill.

    All this happens with the outlet tank set to zero psi.

    Any suggestions?

    I probably filled out the LSA paperwork back in 2006 because I bought a bunch of Ridgid stuff all at once. Will contacting Ridgid do me any good? Thanks.

  • #2
    Just called Ridgid and they say that I registered a bunch of other tools but not the compressor. So LSA is not an option for me. They offered to connect me with a technician but after being disconnected once, routed to the wrong dept once and being on the phone for probably 45 min I gave up.


    • #3
      I guess you don't have anything to prove you did register it.
      "It's a table saw, do you know where your fingers are?" Bob D. 2006



      • #4
        No I don't have any proof that I registered it. Maybe I didn't. It was 13 years ago. Any idea where to start on troubleshooting what's wrong with it?


        • #5
          You may have more than one issue.

          The pressure rising to 150 (which seems high to me) then dropping to 120 is the relief valve popping off at whatever it's set pressure is, probably 120 since that is where it shuts off from your description. The relief valve should have a pressure stamped on the body of the valve. If it says 120 PSI (or PSIG) then that is the pressure that it should start to relieve pressure at. The fact (stated by you) that the pressure rises to 150 then bleeds off to 120 sounds like the relief valve needs to be replaced. A 120 PSI reset for a relief valve with a set pressure of 150 PSI is a pretty wide band and not a 'normal' trip/reset delta. If the valve is stamped 120 PSI then it is not working as it should if it does not start to relieve pressure at 120 PSI. They don't last forever just like the relief valve on you home water heater or boiler if you have one. The contacts on the pressure switch which starts/stops the compressor may also be bad. You may say I hardly use it maybe once or twice a year but that can be part of the problem. The other possible cause is a bad unloader valve. You state that the compressor will not start and the start sequence for these small compressors is usually to open the unloader valve to reduce the motor power required to get them started, making for easier starts and also reduces the cost of the unit because the motor can be smaller.

          But to me it doesn't sound like you have the necessary background to troubleshoot and repair this else you would have figured these points out on your own. Please don't take offense at that I have no idea what you skill level is with mechanical equipment. Your manual should have a troubleshooting section in it that can help you determine what is wrong.

          You may be better off taking it to a repair shop or just trach it and get another one because it will cost you as much to fix this as it would to buy a new one. If you repair you have a working compressor with no warranty. If you buy new you have a working compressor WITH a warranty for roughly the same money.

          The relief valve (Safety Valve) RIDGID shows as in stock and about $16. The pressure switch also shows as in stock and the price is about $50. You may need more parts than this I do not know. But after shipping you are half way to a new compressor so give that a thought.
          Last edited by Bob D.; 09-17-2019, 08:25 AM.
          "It's a table saw, do you know where your fingers are?" Bob D. 2006



          • #6
            Sounds to me like Bob D. covered just about everything.

            I did a search on the Ridgid web site for "OF45150A" and as usual with that site's search function, I found nothing. I did find a newer compressor, OF45200SS and by that number configuration "45200" (the 200 is for the maximum functioning pressure), I presume your "45150" is, as you state a 150 psi compressor.

            So, on initial start, it runs up to 150, but then immediately drops to 120 and the drop in pressure stop there and falls no further, and when the pressure drops through use, the compressor motor does not restart.

            As Bob stated, it appears that you have problems with the pressure switch, which regulates the stop and start of the compressor motor, based on the pressure in the tank. It turns off when it reaches the maximum pressure of 150, but does not restart no matter how far the pressure falls. The question I have is whether there is any indication that it is trying to start?

            I'm a bit rusty, but basically here is how a small commercial compressor system works:

            On the tank, there are generally only three taps; two at or near the top of the tank; one for letting the air in, one for letting the air out. At the the bottom of the tank there is a tap for allowing any condensate to be drained, it is fitted will some type of drain valve.

            The pressure switch acts as the main power switch to the motor (its fitted with an on/off toggle lever generally) and it also functions as the pressure regulator. For the latter, it is internally fitted with a sensor and settings, one for maximum pressure and one for minimum pressure. It may also be fitted with the unloader valve, which I believe is the case with both my compressors.

            So on start, you switch on the power and the pressure switch, which is mounted in one of the taps in the top of the tank senses the pressure in the tank and if it is below the minimum pressure setting, power is sent to the motor which drives the compressor. The compressor then pushes pressurized air thru a line to the tank. Where that line enters the tank, there is a check valve (whose purpose is to let air in, but block air from getting out). When the pressurized air builds to it's maximum point (in your case 150 psi), the pressure switch sensor triggers the maximum setting and shuts off power to the compressor. At the same time, it activates the unloader which dumps all the air from the compressor cylinder as well as that feed line which goes to the check valve. If you pay attention, you can usually hear that air dump when the motor is toggled off at the end of the pressure cycle.

            Then, as you use the pressurized air in the tank, the pressure will fall and when it reaches the minimum pressure setting, the pressure switch will once again power on the compressor and the whole cycle is repeated. How often and to what frequency depends on the compressor's capacity and designed duty cycle.

            So, if the pressure switch fails, it simply won't start OR WORSE, won't shut off. IF it won't shut off, then the compressor continually will run and the tank will over-pressure! In which case the safety valve will blow (hopefully)... and if the safety valve fails (poor maintenance/age) then your tank may just spring a leak or even blow up and we'll hear about it in the news (hopefully not in the Obits).

            If the pressure switch works, but the check valve has failed, then air has bleed out of the tank and back into the feed line and cylinder. The motor simply won't have enough power to turn over a pressurized cylinder... and you'll get that "hum" and most likely a fuse blown or a thermal shutdown as the motor overloads. (The piston simply cannot push against a large amount of pressure on startup... that's why it needs to be "unloaded" at the end of each pressure cycle.)

            The same will happen, if the unloader has failed. The compressor fills the tank to its maximum pressure, the pressure switch senses that and cuts power to the motor, and signals the unloader to dump the air... but it the unloader valve fails, you still have air in the feed line and cylinder.

            This is pretty simplified, but hopefully you get the idea. There may well be other factors, and for that reason alone I agree with Bob... you really should have the compressor properly serviced.

            But as a matter of routine, keep your compressor well maintained. Oil and filter changes, keep that tank drained of condensate, and routinely check the safety relief valve. I have two compressors... I keep them dry and don't let them sit on a damp floor for any length of time. I also keep them clean.

            Note, I did not mention the pressure regulator, which is used after the pressure switch and is on the exhaust line to your tool feed connection. It doesn't generally effect your compressor's mechanical functions, but is used to control the amount of pressure regulated to your particular tool's requirements.

            Last edited by CWSmith; 09-17-2019, 07:11 PM. Reason: Spelling corrections and clarity


            • #7
              Thank you Bob and CW. It was very generous of both of you to spend so much time troubleshooting and explaining.

              Bob - no offense taken. This is over my head.

              CW - You said "you'll get that "hum" and most likely a fuse blown or a thermal shutdown as the motor overloads." I definitely have the hum and probably the thermal shutdown too because I have to unplug the compressor in order to restart it. That must reset something.

              It looks like I could replace the check valve, pressure switch and the unloader fitting for $94. It it likely that those 3 new parts would get me up and running?

              Of course I would have to balance that with buying a new (smaller but probably sufficient for my needs) one for $129 Would this 6 gal, 150 psi, 2.6 scfm unit power a framing nailer and air ratchet ok? That and inflating tires are all I need it to do.

              Thanks for all the help.


              • #8
                Could be the starting capacitor has gone in the thing. Motor humming while under 120psi load would trip a thermal cutoff, but it starts cooled off with an empty tank. Any electric motor repair shop should be able to replace it for far less than the cost of a new compressor.
                Last edited by RDC; 09-19-2019, 06:58 AM.


                • #9
                  I assume the starting capacitor would be part of the switch assembly?


                  If i were to order all the parts discussed above and change them one at a time in what order would you do so? I would hope to change parts until it worked and then return whatever I didnt use.


                  • #10
                    The starting capacitor is under one of those covers on top of the motor. Since it has 2 covers, one is the starting capacitor, other would be a run capacitor. You'd need to remove the covers and get the values off the Capacitors, then either Google them up or hit a local electric motor shop for replacements. I'd just replace them both while you're in there as they shouldn't run you much at all if you look a bit online for them. DO be careful, as those things can still have voltage stored in them even after things have been turned off and unplugged for awhile.


                    • #11
                      OK, I see the capacitors on top of the motor and I think I can replace those if necessary.

                      Attached (hopefully) is a video of what is going on. As someone else stated maybe there is more than one thing going on. I will explain with a little more info that I just figured out:

                      Issue 1: The compressor is rated for a max of 150 psi. When turned on it runs and gets up to 150 and then immediately dumps air until it gets down to 120-125 and holds there. It dumps the air from the valve in the switch assembly. Under the cover there is a little metal plate. When you push the plate down it releases air. That's where it is dumping air to get down from 150 to 125.

                      Issue 2: When air is released from the tank (either by using a tool or by pulling on the relief valve) the motor will not come back on to rebuild pressure. Sometimes it will hum and try to start. Sometimes it will just sit there. Unplugging and replugging it seems to make a difference as it will sometimes restart after being plugged back in.

                      I am willing to buy and swap parts in an attempt to salvage this thing. I hate throwing tools away. But if I have to pay someone to troubleshoot and fix that will obviously not make sense.

                      Does the above explanation and attached video add any new clues? If I were to start replacing parts would it make sense to start with the switch which seems to be the source of issue #1?

                      Thanks again for the generous donation of time and expertise.


                      • #12
                        To me, it looks and sounds like the unloader valve in the pressure switch is defective.

                        I'm hearing the unloader open, but it doesn't close properly as instead of a quick release of pressure, I'm hearing it bleeding out and the pressure drops to 125 psi before the spring over rides and closes the valve. I didn't see the rating on your compressor, but as we previously discovered, the unit IS rated at 150 psi and that is where the pressure should stay upon the initial shutoff, and not bleed down.

                        Unplugging and re-plugging appear to be re-setting the switch so that it activates once again and runs up the pressure, to repeat the cycle. If the check valve was defective, you wouldn't be able to do that as there would still be pressure in that line from the compressor to the check valve.

                        Mind you, I am no expert. I illustrated and wrote, from engineering notes) installation, operation, and maintenance manuals for heavy industrial compressors whose systems are much more complex; and while I've also attended a few field service classes, my talents were more in the realm of making engineering documents more understandable to non-engineer field service personnel. So, understand that my hands-on is minimal. (Note that all my literature did have to be reviewed by no less than four engineers as well as a legal review; however that was more than 20 years ago!)

                        So, with those limitations stated, it looks to me like the tank check valve is working properly (no pressure back to the compressor cylinder, because it did restart). The pressure switch does start the compressor and at the maximum pressure of 150 psi it does properly shut the compressor off. The problem however, is that the unloader valve IS NOT snapping open and closed, allowing a quick dump of the pressure in the feed line... instead it is sticking open and draining the tank.

                        BUT, what I'm not visualizing at this point is the relationship of the unloader mechanism to the pressure in the tank... as the unloader should ONLY be dumping the pressure in the feed line from the compressor outlet to the check-valve. So, something else may well be going on.

                        That said, I'd start with repair (if possible) or replacement of the pressure switch assembly which included the unloader mechanism.



                        • #13
                          "that is where the pressure should stay upon the initial shutoff, and not bleed down."

                          A bad relief valve could also cause a symptom like this.
                          "It's a table saw, do you know where your fingers are?" Bob D. 2006





                          • #14
                            Originally posted by Bob D. View Post
                            "that is where the pressure should stay upon the initial shutoff, and not bleed down."

                            A bad relief valve could also cause a symptom like this.
                            Bob - I am assuming that the relief valve is the little fitting that I have a piece of yellow wire attached to in my first picture. If so, there is no situation where I sense air coming out of that fitting - unless I pull on the wire and release it. Unless you are saying that air SHOULD be escaping and it isn't. And that's causing it to have to be released from the valve that's part of the switch assembly. Would you clarify that for me? I am considering buying some parts and seeing if swapping them makes a difference. Thanks


                            • #15
                              Yes. If the relief valve is not passing air when the compressor reaches normal max pressure (which I assume is 150 because I did not see it listed anywhere in the manual) then it does not sound like it is malfunctioning.

                              Let me ask you this. Once the compressor reaches max pressure and shuts off, can you tug lightly on the wire/string and make the relief valve vent. If yes is it a slight pull which would indicate it is near it's set pressure and ready to go (as it should be if working properly), or does it take significant force to make it vent air which to me would make me think it's hanging up or the spring is worn or some other problem exists. Even though it is most likely the not cause of your problem in this instance, IF it is hanging up then replace it. The pressure switch and the relief valve are the only two devices on most small compressors that protect you from the tank becoming over pressurized and creating a bomb.

                              But on my compressor when it reaches max pressure the relief valve usually pops off for a second or two then reseats (closes). The pressure does not continue to drain off. So I would say (having NOT watched the video) that your valve is OK.

                              Having said that this equipment is 13 years old, and so is the relief valve. If you can afford it I would think about replacing it. And to my way of thinking if you factor in the safety function of it you can't afford not to. But we each accept different levels of risk in all that we do, it's a free country.
                              "It's a table saw, do you know where your fingers are?" Bob D. 2006