AC system or bigger electrical issue?

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Old 06-24-14, 09:24 PM
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AC system or bigger electrical issue?

I will try to keep this simple. I am thinking I will need to find the intermittent short in the low volt system of my AC system. The air handler fuse keeping blowing. But do I have a bigger issue?

Do I need an HVAC guy or an electrician.

Here is the scenario. My house has 2 outdoor units and two air handlers.

upstairs AC and air handler work fine.
downs stairs air handler runs fine on fan mode
downs stairs air handler blows fuse when downstairs AC unit power is turned on and AC kicks in
down stairs air handler blows fuse when upstairs AC unit is powered on.
if either AC unit (upstairs or downstairs) is powered on. Downstairs air handler blows fuse.
upstairs AC and air handler work fine regardless of the the down stairs AC and air handler powered.

Do I need an HVAC guy or an electrician. Is this an issue with my electric service panel?
 
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Old 06-24-14, 10:01 PM
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Welcome to the forums.

Wow.... where do I start.

It's not a problem with your electric service panel.
The two systems should have two separate thermostats and the wiring has no need to interconnect.
I'm guessing that somehow the same heat unit may be controlled from both thermostats.

We're going to need more information.

Are these heatpumps ?
What is the aux heat..... electric, gas, etc. ?

Give us as much info as you can on these two units.
 
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Old 06-25-14, 03:12 AM
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Is it possible / practical to run new thermostat wire from the downstairs thermostat to the downstairs blower unit / air handler ? And then , from the down stairs air handler to the down stairs condenser unit ?

God bless
Wyr
 
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Old 06-25-14, 07:30 PM
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More info

Thanks for prompt replies. I really appreciate it.

More info.

There are breakers for both air handlers , both outside units, and the range top on a second electrical panel that looks to be added after the original construction. 1976.

They are Trane units, manufactured in 1991. I realize I am on barrowed time. But they blow cold when they work. The house sat vacant for 4 years until we purchased it and I was surprised the refrigerent still worked.

They are not heat pumps, just AC. The house primary heat is 220 baseboard. ( ouch on the electric bills)

They air handlers are equipped with heat coils but I don't believe they are wired in. Atleast not to my knowledge when looking at service panels. The service wires for the heat coils are just tied up to the rafters. I suspect that my service couldn't handle the coils and the baseboard at the same time.
 
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Old 06-25-14, 07:40 PM
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Anything is possible, but the thermostat wires would be a challenge unless I can find a way to feed them down through the floor. Air handler is in below ground basement. Thermostat is on 1st floor above crawl space on other half of house opposite basement. Think lots of feet of thermostat wire to pull this off.

So what I am thinking.

Check both outside unites for critter damage and look at the contactor coils. Maybe swap out upstairs AC unit contractor coil with downs stairs AC unit contractor coil. Since it works. Also probably find out how the thermostat wires run to the basement air handler and again look for critter damage in crawl space.

Thanks again for your help I really appreciate it. The HVAC. Guy just wants to sell me new units.
 
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Old 06-25-14, 08:26 PM
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Ok. I think I got it. Upstairs AC and air handler that work have newer thermostat wires running to the outside AC unit. Downstairs thermostat wires that run from air handler to outside AC unit are shot. Wire coating flakes off and are exposed in places. Hopefully the cause of the short.

Step 1. Replace thermostat wires.
Step 2. Take covers off outside units. Test, inspect, and clean.
Step 3. Find new HVAC guy.
Step 4. Thank old HVAC for charging me for a new transformer and not fixing a thing.

Step 5. Sing the praises of this site for helping me out.

Thanks for all the help. I will post again if this works.
 
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Old 06-25-14, 10:05 PM
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Downstairs thermostat wires that run from air handler to outside AC unit are shot. Wire coating flakes off and are exposed in places. Hopefully the cause of the short
That doesn't explain how the two units are interconnected unless all the thermostat wiring is bare and touching. You have two completely separate units that shouldn't share any wiring.
 
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Old 06-26-14, 03:53 AM
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Thermostat wire is relatively inexpensive . And , if you have A/C cool & electric heat ( not a heat pump ) you probably have only 2 conductor tstat wire going outside . With as few splices as possible . Preferably none . Just the termination at the tstat , air handler and condenser .

The tstat wire from the tstat to the AHU probably has 4 or more conductors . Replace with cable with equal or more conductors .

I agree , the 2 systems ( upstairs & downstairs ) should not be inter connected . Hopefully , running all new tstat cable to the downstairs system will isolate them . Although it may not diagnose why it was acting as it was ?

If some one sold you a transformer , check & see if that is correct ?

God bless
Wyr
 
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Old 06-26-14, 04:20 AM
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If you have to change upstairs wiring and can't I have read they have wireless thermostats now. Don't know anything about just heard of them. Thought I would throw this in as a just in case.
 
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Old 06-26-14, 05:26 AM
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I'm not an AC Tech, but, why not disconnect both thermostat wires at each AH, and connect the 2 wires at 1 AH to get it to turn on, and see what happens? Thus eliminating the wires, and thermostats, as a possible cause.
 
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