Power interruption between breaker and ac disconnect

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Old 11-04-20, 05:30 PM
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Power interruption between breaker and ac disconnect

Hi all. I really need some info on this and I'm coming up short finding anything online. My air conditioner spontaneously quit working. After troubleshooting the thermostat and the 24vac transformer, I find no power to my ac disconnect. However, I confirmed I do have 240v coming from the breaker. There's no visible damage to any of the wiring or the circuit board. My house is a 50s style above ground house with a crawl space, I live in Central Florida. Any suggestions on what my issue could be before calling an electrician?
 
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Old 11-04-20, 05:38 PM
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Welcome to the forums.

You have a main panel with a two pole breaker supplying 240vAC to a service disconnect that should be very near the outside condenser. If that is correct...... check for 240v in that disconnect. Make sure you are checking the incoming wiring..... not the wires that go to the condenser. If you don't get 240v..... check from each hot leg to ground. What do you measure ?

It's virtually impossible to have a defective cable..... especially running 240v.
 
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Old 11-09-20, 09:21 AM
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Think I found the problem

I did line test and verified I have 240 coming from the breaker to my outside unit. The contactor appeared burned up and I replaced that. As I was replacing it, I noticed the resistor on the circuit board appeared burned up and a lizard tail sticking out the back of the board. I pulled the board off and sure enough, a lizard shorted the circuit board. I know my power source runs from my breaker to the outside unit, then back in to my air handler. I'm assuming this burned out circuit board is the source of my power interruption. Thoughts?
 
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Old 11-09-20, 10:02 AM
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Excellent chance the lizard caused a failure. After years of doing industrial control box design, I find myself shocked at recent a/c condenser wiring methods. Uncoated PCBA's just a flimsy piece of sheet metal, poorly attached from the outside elements, lizards, etc. Not even a hanging plastic drip panel used. Pretty clearly, just a 5 to 10 year solution at hand.
 
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Old 11-09-20, 12:05 PM
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I hate it when lizards do that.

I know my power source runs from my breaker to the outside unit, then back in to my air handler.
That would be pretty unusual. The most typical split installation is with a furnace, gas or electric, as the air handler with it's own circuit and the condensing unit outside on it's own circuit.
 
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Old 11-09-20, 12:46 PM
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His description is describing a ductless split system.
Those are fed outside and then power and switching to inside.
 
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Old 11-13-20, 12:06 PM
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I'm stumped

I'm officially stumped. I have an older Carrier (installed in 2001) split system with a heat pump and ducting. Both units are connected by a single circuit on the breaker, yet each has it's own disconnect. There is no float switch or door switch on this system. I replaced the contactor and the circuit board on the outside unit as those had obvious damage. I've verified i have 240 from the breaker and I have 240 to my outside unit at the disconnect. Yet I still have no power to the inside disconnect. I live in a 50s style house that has a crawl space underneath. The coil hose housing the power supply appears to run underneath the house. The supply lines are solid copper. I'm 3 weeks in on this problem and I'm stuck. I can't find anything online and because I'm still on furlough due to the pandemic, I have no funds to call in a serviceman. Help?
 
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Old 11-13-20, 12:50 PM
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So, a single feeder somehow makes it to two, separated disconnects. Is the air handler disconnect a fused version? How/where does the feeder split?
 
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Old 11-13-20, 01:17 PM
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The disconnects are non fused. Each one has 2-120 volt lines to run 240 to the system. Where the split is, I'm not sure. The system makes no sense to me and it has run for 19 years without issues other than normal maintenance. The physical lines have continuity, yet no voltage. If I'm understanding that right, then that means no physical breakage otherwise I would show an open line.
 
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Old 11-13-20, 01:25 PM
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Is it not possible to follow the breaker fed feeder to see where it goes? This is unusual, but it may lead to a junction box.
 
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Old 11-13-20, 01:49 PM
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I assume that would involve a voltage detector or wire tracer. If so, that's a tool I don't have. If it's inexpensive enough, I'll happily buy one if anyone has good recommendations.

This whole thing is a mess. The house was built without any type of hvac system in the late 50s. This system was installed in 2001. The house originally belonged to mt grandparents. Thankfully, u still have all the paperwork, but no electrical blueprints among it. So how they ran the wiring is beyond me.
 
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Old 11-13-20, 04:41 PM
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Ok. I feel like a moron right now. I pulled out and went through the original installation paperwork and discovered how they wired the system. They installed an additional breaker on the outside of the house for the air handler! My guess is when the lizard crawled and fried the circuit board, the outside breaker tripped. Switched it off and back on and the air handler is working again. The breaker inside the house is to my outside unit. The breaker they installed next to the power meter is to the air handler. One issue solved.

However now, the system won't engage the outside unit. Yes there's power. Brand new contactor and brand new circuit board. Verified power is running through both. Could it be this lizard shorted my capacitor, too and that's what is causing my outside unit to not engage?
 
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Old 11-13-20, 04:50 PM
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Ok.... we know you have an old Carrier heat pump system.
You mentioned voltage measurement so you must have a meter.

You need to check for 24vAC. You can pull the thermostat off and measure there.
You need to see 24vAC from R to C.
If you don't have a C..... measure from R to Y and from R to G.
 
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Old 11-13-20, 05:09 PM
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All is good. My system has a built in time delay. I've verified everything is working. Heat, cool, and fan. Compressor and fan on the outside unit is functioning normally. Thanks to everyone's input here. This was definitely a learning experience in HVAC. Time for a drink! 🤣
 
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Old 11-13-20, 05:11 PM
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It took a while but you persevered.
 
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Old 11-13-20, 05:12 PM
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In that case, no, not possible the lizard took out the capacitor. Cheers.
 
 

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