HELP...An Odd Problem that None of My Subs can figure out... Compressor issues.

[docperio44]

Hi All, I'm new to the forum and having a problem that is a causing some big headaches with a client (I'm a GC). I'm just so lost right now.

I have a client that wanted to rehab a house to live. When we got in there, the owner told us that the previous owner replaced that both AH and AC 2 years prior but the house sat empty for those 2 years (3 ton, off-brand Carrier unit). After our work, we fired up the units and they seems to run and cool well.

We received a call a few days after the owners moved in that the outside unit was making a humming noise and vents were blowing warm (I have a video). A sub contractor went but the machine was working fine and he installed a hard start in the event the comp was struggling to start. The client then called again and said the machine continued to hum but when restarted, it would work. However, at times, the compressor didn't start at all (fan blow only -- over heat).

These are 2 faults that continue to this day... and sporadically every time I go the machine is cooling well and compressor behaves. : Either 1. The compressor struggles to start and makes a loud hum sound. or 2. Compressor doesn't start, only fan runs and compressor temp is overheated and can restart by cooling down compressor.

This problem continued with multiple subs trying different things. One sub said the compressor was bad, and it was replaced under warranty. SAME THING HAPPENED with the new comp. Another sub replaced contactor, capacitor, and other sub played with the amount of gas. SAME

FINALLY, the homeowner decided he wanted to CHANGE the unit. My sub calced the square footage of the home and decided a larger unit was needed. A 5-ton Rheem was installed with new wiring and piping. More venting was created. We even had the electric line monitored by the local power company to ensure that wasn't any issue with either of the phases that run to the house. AND STILL THE SAME PROBLEMS INTERMITTENTLY occur. Once a day or once every 2 days.

I replacement the electric panel, thermostat.... and I can't think of anything else. I'm being threatened with a law suit as my sub was the one that talked them into the larger unit.

I have brought different subs (4 in total) and no one can figure it out. Most recently, a balance test and CFM test were done and this contractor said the machine wasn't moving enough air. My first that was that this wasn't the issue cause I would think the machine would start to freeze.

I'm 10000% LOST and losing money like no other. I have more details if needed.... sorry for the winded post.

[pecmsg]

From 3 tons to 5 tons and it’s moving enough air?

[Juan Madera]

Happen at the same time each day?

And..... bad move allowing someone to replace a 3T with a 5T as this generally compounds the issue.

Are there no qualified A/C techs in your 'hood?

[Olivero]

Wow.

That's quite something.

Is it a 3 phase compressor or single phase? I'm guessing it's single if it has a start capacitor.

The only reasons a compressor won't start is,

A: it's locked up.
B: It's got no power or not enough.
C: The capacitor is bad and it can't get it's "Kickstart"
D: An incomplete circuit, which would be compounded to B.
E: Intrenal safety went off.

There's not much else, you can get into details of why each point is what it is, but there's not much else.

Did you get new T-stat wire pulled when the new unit went in? A Licensed electrician once beat into my skull so thoroughly and made me repeat it about 100 times that an intermittent problem is ALWAYS a loose connection.

You replaced all the hardware when a new unit showed up, could be it's short cycling on the extreme, compressors don't like that and it will wear it out really, really fast, a loose wire or a semi broken wire can do that, it'll make a connection, break it, make it, break it, etc.

Ohm out each wire from the T-stat to the condensing unit, it's gotta be something OTHER than what you've replaced so far, so find out EXACTLY what the subs did, each one, and make a list, post that list here and I'm sure we can tell you what else needs checking.

My first thought is bad wiring and severe short cycling, that's the only thing making any sense considering the problem hasn't changed at all.

[ammoniadog]

Is this thing running off of a Nest thermostat?

Just a hunch.

My second guess is that the home owners are crazy and the noise is coming from something else. Maybe a sump pump?

My third guess would be that this is a heat pump and when you say warm air is blowing out of the vents, the unit is actually going into heating mode and it's the reversing valve that's humming. Or perhaps they are running it in heating mode on purpose and it's going into defrost periodically and doing what it's supposed to. Could it be that the thermostat has an "auto" mode to switch between heating and cooling automatically, and it's bouncing back and forth? Maybe the stat is in a dumb place with a vent blowing on it or a light bulb is pointed at it or it's too close to something else that produces heat?

Either way, I agree with the others that imply that it was probably nuts to go with a larger unit.

Most ducts are undersized from the start for whatever system a house originally comes with. I know you said they added more vents, but it would take a considerably larger duct system to go from 3 tons to 5. Hopefully whoever did this knew what they were doing and has some real load calcs to back it up.

Good luck!

[rider77]

Please post the commissioning report for this unit that was just installed

[poppa]

hire a qualified sub

[pacnw]

Manual J
Manual D

Model and serial number of the old equipment, if available, and the new equipment.

House size and location if neither of the above(but should have that if the sub "calced" it).

Most likely oversized equipment on undersized ducts.

[beenthere]

When you say only the fan runs. Do you mean the indoor fan, or the outdoor fan?

We’re the low voltage wires from the thermostat to the out door unit replaced ?

[Makeitcold]

Agree with previous posts about your low voltage side. I would be getting a proper commissioning report written up from the installing company showing the refrigerant charges and airflow are correct for your records as I think in all likelihood enlarging the system by 60% is going to create an S-storm of problems. Get a copy of their completed load calculations as well

[docperio44]

Is this thing running off of a Nest thermostat?

Just a hunch.

My second guess is that the home owners are crazy and the noise is coming from something else. Maybe a sump pump?

My third guess would be that this is a heat pump and when you say warm air is blowing out of the vents, the unit is actually going into heating mode and it's the reversing valve that's humming. Or perhaps they are running it in heating mode on purpose and it's going into defrost periodically and doing what it's supposed to. Could it be that the thermostat has an "auto" mode to switch between heating and cooling automatically, and it's bouncing back and forth? Maybe the stat is in a dumb place with a vent blowing on it or a light bulb is pointed at it or it's too close to something else that produces heat?

Either way, I agree with the others that imply that it was probably nuts to go with a larger unit.

Most ducts are undersized from the start for whatever system a house originally comes with. I know you said they added more vents, but it would take a considerably larger duct system to go from 3 tons to 5. Hopefully whoever did this knew what they were doing and has some real load calcs to back it up.

Good luck!

YES... it is on a Nest. Curious as to why you asked that?

[docperio44]

When you say only the fan runs. Do you mean the indoor fan, or the outdoor fan?

We’re the low voltage wires from the thermostat to the out door unit replaced ?

I meant outdoor, sorry. Actually, no, LV was not replaced. Seems like you have a hunch about something.,,,, maybe??

[docperio44]

Wow.

That's quite something.

Is it a 3 phase compressor or single phase? I'm guessing it's single if it has a start capacitor.

The only reasons a compressor won't start is,

A: it's locked up.
B: It's got no power or not enough.
C: The capacitor is bad and it can't get it's "Kickstart"
D: An incomplete circuit, which would be compounded to B.
E: Intrenal safety went off.

There's not much else, you can get into details of why each point is what it is, but there's not much else.

Did you get new T-stat wire pulled when the new unit went in? A Licensed electrician once beat into my skull so thoroughly and made me repeat it about 100 times that an intermittent problem is ALWAYS a loose connection.

You replaced all the hardware when a new unit showed up, could be it's short cycling on the extreme, compressors don't like that and it will wear it out really, really fast, a loose wire or a semi broken wire can do that, it'll make a connection, break it, make it, break it, etc.

Ohm out each wire from the T-stat to the condensing unit, it's gotta be something OTHER than what you've replaced so far, so find out EXACTLY what the subs did, each one, and make a list, post that list here and I'm sure we can tell you what else needs checking.

My first thought is bad wiring and severe short cycling, that's the only thing making any sense considering the problem hasn't changed at all.

Great info.... BUT NO, they didn't pull a new T-stat!!!! What's your thinking there? And it was on a NEST as well. I will OHM out the wires.

I'm not too familiar with short-cycling. Is the potential bad-wiring the cause or the effect?

[pecmsg]

°

[BNME8EZ]

°

This is funny.

I saw an ad for a Home Warranty company and when they mentioned A/C repairs they showed a lady tapping on a Nest.

[ammoniadog]

YES... it is on a Nest. Curious as to why you asked that?

Nest thermostats have been known to cause oddball issues that don't seem to make any sense. There's a chance that the nest is sometimes causing the contactor in the outdoor unit to only partially pull in which might explain some of the weird stuff that's happening.

When I hear about oddball stuff happening with hvac stuff that doesn't seem to make any sense, the picture that pecmsg put up is usually the first thing that pops into my head.

I can't say for sure the nest is causing it, but it'd probably be the first thing I would suspect.

[docperio44]

I changed it to a regular tstat on sunday. and it hasn’t failed yet. fingers crossed! thank you!

[Olivero]

I changed it to a regular tstat on sunday. and it hasn’t failed yet. fingers crossed! thank you!

Yeah the idea is the T-stat is what controls everything in a way. it's the control center of everything so if it fails or acts up it affects the system.

I don't have experience with NEST at all but i've heard enough on here to stay away from them.

The idea with the LV (Low Voltage from and to the T-stat) is that those wires control everything as the T-stat is the brain, the wires are the arms you can say so if the wires are damaged or shorting they can cause short cycling which is when the compressor starts and stops, start then stop, it kills the compressor in short time and it overheats it as it can never really cool down due to not getting any refrigerant flow through it, it also fails to cool as it never really runs.

The thing about it is it's most likely a control issue so if the new T-stat doesen't solve it, have a sub pull new low voltage wires, all of them get replaced so you KNOW. Even if you ohm them out you could be ohming it out right when it's connected and as soon as the wind shifts or something happens, the wire breaks apart again and everything shuts down.

So if the new t-stat doesen't do it, then get new low voltage wiring.

And slap whatever contractor installed that new system without even checking with anyone what might be causing it, you as the GC are solving their problem for them. Or send them a link to this site and they can learn something.

[Olivero]

What happened? Did it get fixed?

Was it the Nest?

[kdean1]

My experienced guess is the Nest was the problem all along. My experiences with Nest have led me to tell customers I won’t guarantee new equipment on a Nest.

You must still determine if the equipment and ducts are the right size. Oversized equipment is bad. Undersized ducts are bad. Ask a contractor you hire HOW they determine sizing.