Messed up today

[hurtinhvac]

And learned a hard lesson.

Targeted the "txv subcooling" listed on the data plate and got there rather quickly - really only throttled it a couple/times and I was preparing to let it run for a bit and there it was. Suction line started sweating (which is all the client really wanted to see) and I was bleeding the hoses back into the system when the compressor screamed, thumped horribly and tried to jump out of the coil at me and the head pressure took off like a rocket. Right in front of the very worst kind of client, whose house is right across the street from where my boss used to live - knows him well and called him probably five times the rest of the time I was there.

I failed to note it was a fixed metering device despite what the data plate said. Recovered until I arrived at target superheat and system started operating normally. But the damage was done in the eyes of the customer.

Very embarrassing. The rest of the day was very long, during which I obsessively identified metering devices.

[jimj]

You should ALWAYS be looking at both, SC and SH! A good leason learned.:cheers:

[thermojohn]

There you have it. There are many trade secrets all of us Professional Members here at H-talk have. You have passed the initiation process. Now apply for Pro and learn much more! :.02:

[gravity]

:deadhorse: you should also be starting inside at the air handling unit checking filters, airflow, and what metering device your working with.

but im with you. homeowner followed me around today. we got to the outdoor unit and i had like 65/140 psi pressures with sc; 13* sh; 30* i diagnosed quickly clogged drier or txv.

i said hmmmmm lets take the door and cover the top of the unit.

pressures jumped to 68/195 with sc still at 13* but sh came down to 10*

outside was ~ 62* and no load really inside. unit was high efficient too.

doesnt sound like my first 2 conclusions were correct.

[zw17]

There you have it. There are many trade secrets all of us Professional Members here at H-talk have. You have passed the initiation process. Now apply for Pro and learn much more! :.02:

Ohhh... I get to teach him how to shred a few cylinders in a 60 ton semi hermetic and the follow up lesson will be the cost of overnight air freight to replace said compressor.

Yup, it happened to me.

I bet you will NEVER make that mistake again, I know I learned from mine.

[thermojohn]

Ohhh... I get to teach him how to shred a few cylinders in a 60 ton semi hermetic and the follow up lesson will be the cost of overnight air freight to replace said compressor.

Yup, it happened to me.

I bet you will NEVER make that mistake again, I know I learned from mine.

That hurt. I burnt a perfectly good 30 HP Copelametic by wiring the part windings out of phase. Just so happened there was a hella thunder and lightning storm that afternoon. Wonder what caused that compressor to take a dump? :whistle: Lucky for me and a lesson learned. I pay attention to part windings and phasing now!

[chaard]

:deadhorse: you should also be starting inside at the air handling unit checking filters, airflow, and what metering device your working with.

but im with you. homeowner followed me around today. we got to the outdoor unit and i had like 65/140 psi pressures with sc; 13* sh; 30* i diagnosed quickly clogged drier or txv.

i said hmmmmm lets take the door and cover the top of the unit.

pressures jumped to 68/195 with sc still at 13* but sh came down to 10*

outside was ~ 62* and no load really inside. unit was high efficient too.

doesnt sound like my first 2 conclusions were correct.

With those numbers low load would be first conclusion, especially when its below 70*. You'll see more systems running like that this time of year. Besides a restriction in the liquid line would show high head.

[zw17]

That hurt. I burnt a perfectly good 30 HP Copelametic by wiring the part windings out of phase. Just so happened there was a hella thunder and lightning storm that afternoon. Wonder what caused that compressor to take a dump? :whistle: Lucky for me and a lesson learned. I pay attention to part windings and phasing now!

As I don't use a recovery machine to force liquid refrigerant into the suction side.

It was such a busch league rookie mistake.

[manny2326]

The client wanted to see the suction line sweating? normaly I would tell those types of people to let me do my job and to stand back. I am so glad that I dont have to deal with residential or even commercial clients that think that they are hvac techs anymore. I think that this is one of the reasons that I am so happy with supermarket refrigeration.

[gravity]

With those numbers low load would be first conclusion, especially when its below 70*. You'll see more systems running like that this time of year. Besides a restriction in the liquid line would show high head.

oh geez here we go again!

[jimj]

oh geez here we go again!

LOL. :grin2:

[Makinhole]

No one ever told me you have to remove the scale from the case in order for it to be accurate....severely overcharged...OOPS the compressor sounded like my 76 chevy luv pickup the last 100 yards it ever ran..:whistle:

[ChrisTechMech]

My stupid mistake. I trusted a customer. Enough said? I had a leak, added 300 psi nitrogen, didn't drop 5 psi in an hour, couldn't find the leak, scheduled to come back in 24 hours to see if it was really leaking or if maybe neighbor kids were releasing it. I didn't pull the disconnect because the house was locked up when the customer left and I didn't have anywhere to store it (flipping it wasn't an option, it would power the unit either way). I talked to the customer before he left and he understood the compressor would "blow up" if he ran it. I already shut it off at the stat and figured it would be fine. I was way too trusting back then. Wifey got hot and decided to try to run the A/C even though it hadn't worked in 3 days already. You know the rest. For as angry as I was at that customer's wife, I was even more mad at myself for not just disconnecting the t-stat wire on the contactor. :gah:

[keeplearnin]

Here's a good trick for customers who like to look over shoulder. Excuse me sir or mam could you please go look at the thermostat and check temperature I will come inside in a couple of minutes.

[chaard]

oh geez here we go again!

Pardon me. My ADD is showing.

[hurtinhvac]

I feel a bit better now. And you can believe I was paying close attention to every metering device I came across today - the very first one being the same set up. However one of our most experienced techs wrote the piston size of the metering device big as day on the coil case.

Didn't mean to start another restriction debate...

What should I be paying particular attention to when checking systems in low ambient temps?

I applied for pro a few days ago and am looking forward to more schoolin' - it never ends, does it?

[gravity]

you can use this formula when checking a piston.

superheat = (return wb temp x 3) - 80* - OAT) / 2

ret wb = 60*, OAT=85*

60 x 3 = 180, 180-80=100, 100-85=15, 15/2= 7.5* superheat

also verify you have 400cfm per ton and make sure your at minimum operating pressure/temperature.

[thermojohn]

you can use this formula when checking a piston.

superheat = (return wb temp x 3) - 80* - OAT) / 2

ret wb = 60*, OAT=85*

60 x 3 = 180, 180-80=100, 100-85=15, 15/2= 7.5* superheat

also verify you have 400cfm per ton and make sure your at minimum operating pressure/temperature.

Is this airflow determined by something other than factoring EWB, and temp split to determine if airflow is correct?

[gravity]

my brain aint working to good right now. i dont understand your question.

i do however check airflow with static pressure first to determine the units cfm. i then will charge accrodingly.

[hurtinhvac]

my brain aint working to good right now. i dont understand your question.

i do however check airflow with static pressure first to determine the units cfm. i then will charge accrodingly.

What do you use to check static pressure? Pressure tips and digital dual port manometer, by chance?

I sincerely appreciate all the feedback and hope it continues for a bit.

But I just went off call as of 8 this AM, the Mrs. has been missing me and I've been missing my adult beverages {urp}.

[gravity]

oh. i use a testo 510 and the dwyer static pressure tips