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Re: compressor hard to start when cold
Sounds more like the pressure relief valve that takes the air pressure off the compressor upon shut down so when it re-starts there is no pressure until the motor gets a start this is known as a unloader valve and is usually a small brass valve that looks like a fitting and will hiss on shutdown,if it sticks the motor trys to start with the load of the air pressure on it and slips the belt due to load
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Several things to check. Check amp draw with meter to make sure that the reset is not bad. It amp meter is showing low amp draw when it trips, then replace reset. If reset is good check condition of the cold start valve. The valve will not allow pressure to build until motor is at full rpm and the pump is making good pressure/volume. If cold start valve does not close, check pump for leaking or broken reed valves. If cold start valve is good, check the capacitor for at least 10 percent of rated valve. Low pressure /volume is usually leaks from tubing or leaking /broken reed valves or burned gaskets in the head of the pump. Finally, make sure that the check valve or non-return valve is not leaking pressure from the tank causing back pressure. Good luck
check the breaker it needs to be motor rated for the surge on start up this will also be higher when motor is connected to the pump due to the extra torque placed on motor plus when cold oil losses viscocity and thickens therefore placing even more torque on motor
Rmove the drive belt and check the motor. It should turn very freely by hand and if turned on should start up easily. If it turns hard check the armature bearings if it starts slowly but turns OK after you give it a push, you have a bad start capacitor. If the motor is OK check the pump. It should turn fairly freely except on the compression stroke where you should feel slightly more pressure is needed to turn it. If you can't turn the flywheel or it turns very hard, you should check the connecting rod to crank shaft joint and crank shaft bearings. These usually go bad if there is low or no oil in the crank case.
In the back of the compressor motor you will see a fan, remove the plastic cover to get to it..
Once you have the plastic cover removed and the fan exposed, plug the compressor in and spin the fan with your fingers...be quick as the fan could cut your fingers if you do not get them out of the way..
If the compressor starts working, then the start capacitor is bad on the compressor...if it does not run then you have motor troubles, either replace the motor or get it rewound.
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Turn the compressor pump pulley by hand (with belt off) and air pressure in the tank. It should be very easy to turn. If it is hard to turn, evaluate the check valve for leak. If no leak examine crank bearings for damage. Repair as needed. If easy to turn fault is with motor. Check amp draw with belt removed. When the motor comes on, it should draw about 15 amps and drop lower. The motor should start and reach full rpm in a split second. It should start with a bang and run smoothly with-out getting hot and only pull low amount of amps. If slow start and high amp draw, check capacitor/s and or start winding switch inside of motor. Sometimes the start switch will burn the contacts and give trouble. If both capacitors test within 95% of value and start switch appears to be good, look for damaged copper windings. Windings will be discolored or burned and the tie strings binding the windings will be melted. Replace as needed. Good holidays
May have a bearing going bad. Remove the v-belt and turn the motor by hand. Does it turn hard or produce an unusual noise. If so you have a bad motor bearing. If not turn the pump by hand. If it turns hard or produces an unusual noise you have a bad bearing in the pump. Also move the pump fly wheel up and down , left and right. If you can move it the front bearing is bad.
IS IT THREE PHASE OR SINGLE PHASE? MOTOR TAG WILL SAY PH 1 OR PH 3.DOUBLE BREAKER OR TRIPLE BREAKER WILL ALSO TELL. IS THIS A BRAND NEW INSTALL OR AN EXISTING COMPRESSOR THAT JUST NOW STARTED DOING THIS. SOUNDS LIKE A POWER PROBLEM LIKE A MISSING PHASE OR BLOWN FUSE. REMOVE FUSES WHEN OHM CHECKING - DONT TEST THEM WHILE STILL INSTALLED.