my tempstar roof top a/c stage of my roof top unit doesn't start. I replaced the transformer and the thermostat, and it still won't power up. is there still more I should check, like the capacitors (the compressor capacitor), any in-line fusible links ? thermal cut-outs, or overload cut-outs? other relays I don't know about?, the main relay swith, should I replace that? I know it's dirty and gummed up and I should clean it completely.
My tempstar rooftop a/c unit
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I agree with beenthere. You need to determine where the electricity is and isn't getting to. If it is a bad capacitor which would mean that the unit is receiving power into it and across the contactor when the stat is set for cool and calling, you will need a digital multimeter to test that cap and just so it is said, please make sure you turn the power OFF to the unit, not just by way of stat but by breaker or disconnect, before you go messing around.
A capacitor can only properly be checked with ALL wires disconnected from it so write down what wires are on what what terminals and get a good mental image of them before you remove any of the wires and with a digital multimeter that reads mfd aka microfarads you will check the cap. Once all wires are off of the capicitor, the cap needs to be discharged by sticking a screwdriver across the poles. Test across herm and com and test between fan and com and get your readings. You have to hold the leads on the terminals for a few seconds to receive your readings. The proper mfd numbers should be labeld on the cap already to match your readings against.
Nothing should ever read between herm and fan as if it does than the cap is bad, if it's a dual run cap meaning both the compressor (herm) and fan are running on one capacitor.
Now if your contactor is not pulling in when the stat's set point is calling for the system to come on in cool than you have a different problem which any of us on here will assist you with as needed. You know how to tell if a contactor is in or out or if it's good or bad? I can tell you but I might have to charge you for that class.
Good luck and ask away.
A capacitor can only properly be checked with ALL wires disconnected from it so write down what wires are on what what terminals and get a good mental image of them before you remove any of the wires and with a digital multimeter that reads mfd aka microfarads you will check the cap. Once all wires are off of the capicitor, the cap needs to be discharged by sticking a screwdriver across the poles. Test across herm and com and test between fan and com and get your readings. You have to hold the leads on the terminals for a few seconds to receive your readings. The proper mfd numbers should be labeld on the cap already to match your readings against.
Nothing should ever read between herm and fan as if it does than the cap is bad, if it's a dual run cap meaning both the compressor (herm) and fan are running on one capacitor.
Now if your contactor is not pulling in when the stat's set point is calling for the system to come on in cool than you have a different problem which any of us on here will assist you with as needed. You know how to tell if a contactor is in or out or if it's good or bad? I can tell you but I might have to charge you for that class.
Good luck and ask away.
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Btw, you are staring at this system not starting as if this is an electrical problem. If you have a low pressure switch on this system and your system is very low on refrigerant which would trip that low pressure switch than your unit will not start until refrigerant is added.
You will need a set of refrigerant gauges to check to see if you have refrigerant in the system in the first place but in all honesty, unless you are EPA certified you should not be hooking up to any ac system.
You will need a set of refrigerant gauges to check to see if you have refrigerant in the system in the first place but in all honesty, unless you are EPA certified you should not be hooking up to any ac system.
Why do people always replace things before investigating? Did you not have 24v on the secondary side of your transformer? Was the t-stat not sending out 24v when you turned the cooling on? If you t-stat was lit up then your transformer was working because that's usually where you power the stat from. Check any manual safety's and see where you do and don't have voltage when cooling is enabled. Do you have 24v on y1 and g for your fan?
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