Seems to be 120vac from red to ground and 120vac from black to ground but no voltage between red and black, which should be 240vac. Reading was taken at the external dissconnect. What might cause this?
Thanks, S
If red is L1 and black is L2, it seems like you don't know how to use a volt meter properly.
If the disconnect is not thrown , UM could be right, something is letting the voltage through to the other side.
If the disconnect is thrown, then one side is the real voltage, and the other side is probably the 'phantom' voltage caused by the high impedance of the meter picking up the induced voltage on the wiring.
One side could be open somewhere.To find out which, take a light bulb, anywhere from a couple of watts up to 100 watts and put across the line from L1 to neutral and then L2 to neutral. Do that on the 'hot' side of the disconnect.
Could be the breaker is bad, needs to be reset, or if fuses are used, one bad fuse.
Sounds to me like someone moved the 2 pole breaker and it's not on both sides of the line. Both black and red are on the same side of the service.
Is the disconnect open or closed?
"Detective?" - "Defective" is more like it. I'll bet you couldn't detect your way out of a used refrigerator carton even if both ends were open.
S
I did a lot of reading on this and UM is right - it's called backfed voltage and it's a problem peculiar to 240V wiring. It could easilt account for the problem since the circuit label shows a crankcase heater.
Checked the fuses, checked the breaker but couldn't find anything wrong. Wife is insisting I call the pros. Will let you know what they find.
S
Nope. It failed without any manipulation.
S
One leg is dead and you're reading voltage through the crankcase heater. make sure the disconnect is off before checking the voltage. Read the voltages at the circuit breaker feeding the external disconnect. One side could be tripped or there is a bad connection. Turn the breaker off forcefully to make sure it clicks and resets if it tripped before. Sometimes, a 2 pole breaker will trip and if you don't use enough force when you turn it off, one side may not reset. I've seen it happen more than once. ?(?)?
[8~{} Uncle Broken MonsterYou're clearly the HVAC pro here. I will double check the 2 pole breaker. That could explain a lot. Thanks!!!
S
Open and closed, with fuses and without and the fuses read about 1 ohm so I think they are good. It's all moot now since the A/C guys are coming - my window of opportunity passed - the wife wants the AC back YESTERDAY.
S
One trick to test fuses is to check voltage from one end of the fuse to the other. It would be the same method as a continuity test. So I've been told anyhow. Have you ever tried the end to end voltage test?
That works if the fuse is in a complete circuit, you'd get 0 V if the fuse is good, full line voltage if it's open. But if it's not a complete circuit, then you'd get zero either way.
That trick might be a bit more useful checking points in relays or contactors. I've always checked fuses by ohms or line to ground or line to line voltage.
Won't work if there is an open circuit either before or after the fuse ----
Did that, About 1 ohm for the both of them. I think there's an intermittent open in the cable in the conduit from the breaker panel to the outside disconnect. Decided that it needed a recharge anyway so I'm calling the HVAC folks tomorrow.
SThanks to (almost) everyone who replied - it's in the hands of the HVAC guy now. SWMBO wants cold. And as Dirty Harry once said "A man's got to know his limitations."
S
refrigerant does not get used up.
If it needs a recharge, it has a leak. Fix the leak.
(or it wasn't charged properly in the first place. But the leak is likely.)
While somewhat expensive at about $ 100 for a casual home user, I like the Fluke T-5 tester. Just set it for ohms and put it across the fuse. If it shows low ohms, the fuse is probably good, if it gives you an overload indication, the fuse is probably bad. The meter is almost blow up proof so that test works fine. I and several others where I worked do it all the time on circuits up to 480 volts and never had a tester to fail.
For the simple meters or even the neon bulb type testers, go from each side of the fuse to the neutral wire. If it shows power on both sides, then go across the fuse and if it shows power, the fuse is bad. If any doubt, just pull the fuse and check it with an ohm meter. Should be very close to zero ohms.
I would not be surprised if one or more bad capacitors are found.
Nor I but I don't have a way to test them easily whereas an HVAC guy with a truck probably has spares he can just swap test. Probably can meter it, too. I figure it's always worth looking at stuff like this in case it's something easy. It never hurts to learn the terminology. Three days ago I didn't know about backfeeding and crankcase heaters on A/C's so it wasn't a total loss mucking around but I suspect I will be charged the "you tried doing it yourself first" fee. I'll just say "I took it apart to help you - you owe me an pre-diagnosis assistance discount!" (-:
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