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Thread: pressure problem, setting the switch

  1. #1

    Default pressure problem, setting the switch

    I have a Heat pump unit with a shallow well pump. My pressure switch burnt out and I had to replace it(I also replaced the check valve and some plumbing). Ever since then when my AC first kicks on, my pump turns on and off like 10 - 15 times before it finally just stays on. Ofcourse pressure build up is cutting it off.

    I guess it is my in-line valve that is bad. What do ya think?

    Back to the subject matter. How do you set the pressure switch? I have 2 screws, one a cut-in pressure and the other a cut-out pressure. Could someone give a little detail on the procedure to set 20/40 settings?


  2. #2
    Previous member
    Join Date
    Jul 2005
    Riverview, Fl.


    Hi Brrrett,

    I am new to this forum and don't know yet if advertising is allowed so I copied a Q/A from my FAQ page on how to set the switch.

    Keep in mind, that rapid hammering is probably form the switch being set too low. Try to get it up high enough so the pump can still shut off when the AC goes off, but no higher than 75 PSI.


    Q. How do I adjust my pressure switch?

    A. Since Square D is probably the most popular pressure switch on the market, that’s the one we will talk about.

    With a bladder tank, you will have to shut off the pump electrically. Open a faucet and let all the water out. When there is no water pressure left, take a tire gauge and check the air pressure in the bladder tank. Depending on what pressure you want your pump to turn on at, add air until there is two pounds less in the tank than your turn on pressure. Example: for 40 on and 60 off, air the tank up to 38 psi. Take the plastic cover off the switch. Under the cover are the points and the adjustment nuts. With a 3/8” nut driver, turn the nut on the tall spring clockwise several turns. Turn the pump back on until it builds water pressure and turns itself off. Open a faucet and watch your gauge. When you hear the points click closed, that is the pressure on setting. Keep adjusting until you get the desired on pressure setting. At this point your pressure switch should be turning your pump on and off with a 20 pound differential. If you would like to take the off pressure up a little more, you can turn the nut on the short spring clockwise and cycle the pump a few times until you get the desired pressure. I wouldn’t go beyond 70 psi and I wouldn’t spread the differential out more than 30 pounds. Note: some bladder tanks won’t let you get much more than the 20 pound differential. You don’t want to top the bladder out. That puts excessive strain on it and will shorten it’s life.

    If your adjusting a switch with a galvanized tank, you can disregard the part about letting all the water out and checking air pressure etc.

  3. #3


    Thanks so much Bob. I had the settings backwords. So once I figured that out it works great now.

    Thanks guys.


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