Hot Topics: AC Won't Turn On Hot Topics: AC Won't Turn On

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Original post: AC not turning on

Gecko316 Member

This is a rental unit and occupants trashed the place, I suspect the AC has been out for many months.

Nothing happens when I turn on the AC at the thermostat. There is no noise and it doesn't trip the breaker or anything (I reset the breaker also).

I’m not sure what steps to take first. The AC was purchased new at the end of 2010/start of 2011.

Houston204 Forum Topic Moderator

Is the low voltage wire even connected to this unit?

Gecko316 Member

I don't even know what a low voltage wire is. I will probably just get an HVAC person to come and check it out.

Houston204 Forum Topic Moderator

I believe it showed in AC4 JPEG.

Roughneck77 Member

I see an aftermarket high-pressure cutout control that’s been bypassed, but the other pictures don’t show anything.

You’ll need some tools and a meter to troubleshoot. Do you have those things?

I don’t see a control wire going into the unit either.

Houston204 Forum Topic Moderator

A faulty AC unit.

The yellow arrow is pointing to the most likely location of your control wire.

It usually looks more like this but your wire is in a plastic conduit.

A faulty AC unit.

It will usually connect to the condenser with a couple of orange wire nuts.

A faulty AC unit.

Turn off the thermostat before trying to reconnect the two wires or you might pop a fuse in the indoor unit. Usually, it's 3 amps for gas furnaces and 5 amps for air handlers.

A faulty AC unit.

Gecko316 Member

Here is a picture of the run capacity and the control wire.

A faulty AC unit.

Last edited by PJmax; 07-02-18 at 11:13 AM. Reason: added labeled pic from link.

PJmax Group Moderator

The two connections I circled in red are the 24vac that activates the contactor. I don't see any protection devices, like hi/lo pressure switches, connected.

I also only see one single capacitor. Is there a second one elsewhere on that unit?

The connection I circled in white looks to be a connection that would normally be on a capacitor.

You may be in need of some "hands-on" professional help there.

Houston204 Forum Topic Moderator

Looks like a dual cap on my iPad.

I have seen some serious issues when the low voltage wire is run in the same whip as the high voltage wire.

Water got inside of the whip and shorted the high voltage with the low voltage.

I had to replace the contactor, the thermostat, and the furnace control board.

I hope this is a very different issue.

Gecko316 Member

I had the HVAC tech come and check it out. He got the unit running from inside the garage but could not get it working from the main thermostat.

The previous tenant was running something very illegal, there were new vents in the garage and wiring that led to what most likely used to be an alternative thermostat.

The HVAC tech seemed really honest and stated that the whole unit would need to be replaced because:

1. It was very old, likely from 1986 when the house was built, the flue inside the garage needed to be replaced and they don't make them anymore. He said it would be dangerous to operate — if there was a leak, the house would intake carbon monoxide.

2. The evaporator coil is corroded.

3. The condenser is almost 8 years old and uses R-22 refrigerant which may not be a problem now, but won't be available to use in the near future.

He also stated that other AC companies may offer to fix it, but he couldn't do it because he wouldn't be able to sleep at night.

It is mounted to the garage's ceiling, not a freestanding AC/heating system.

Any thoughts? Do I just trust this guy or get a second opinion?

There was no charge for the service call, and he was out there for around an hour.

PJmax Group Moderator

Looks the furnace was from 1986 but the AC was either replaced or installed at a later date if it was only 8 years old.

A condenser being 8 years old and R-22 are not issues.

A corroded evaporator, and I guess leaking, is a problem.

Should you trust the guy? Probably but you should get a second estimate to replace existing equipment.

Roughneck77 Member

So what did he find was keeping the unit from running?

Gecko316 Member

I think it was just the thermostat not wired up to the house

But yeah, I will get another estimate. If they can fix it and it's safe, I will go that route.

I think he manually turned it on using the wiring from the thermostat that used to be in the garage

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