Apprentice Is Sometimes Right.

GBart

We have some students working in the field, one told us of a situation he find himself in.

He was sent out with a subcontractor to a AC call at an older office building. Older R-22 system, they go into the office and they note that the ceiling panel under the airhandler is stained and wet and the technician says let's go to the roof and brings gauges and R-22.

They hook up to the unit for that office and find, on a 74F ambient day that the suction pressure is 80PSIG and the head pressure is 350PSIG but the condenser doesn't seem to be moving any heat, the technician says they have to ADD refrigerant and has the apprentice hook up the gauges and start charging in VAPOR........then the compressor seems to die, ( there is an empty R-22 can laying on the roof by the way). He blames the apprentice.

Your thoughts?

STEVEusaPA

The tech is responsible for the apprentice. What was the tech doing while the apprentice was hooking up the gauges?

SuperJ

Probably tripped the high pressure cut out when they added refrigerant. 350psi seems really high for a 74F day on r22. Might already be overcharged.
Did they get a superheat/subcooling measurements?

GBart

SuperJ said:

Probably tripped the high pressure cut out when they added refrigerant. 350psi seems really high for a 74F day on r22. Might already be overcharged.
Did they get a superheat/subcooling measurements?

Nope the guy just looked at the gauges and decided to add refrigerant, 350 is high for 22 on a hot day, high pressures do not indicate low refrigerant, could be it's full of non condensables.

EBEBRATT-Ed

The tech is an idiot. R-22 with a clean condenser will run about a 275-280 head at 90 degree OA. If you get over 300 your in trouble. The 80 lb suction is due to the high head pushing the suction up.

Dirty condenser, condenser fan problem or overcharge would be my guess, especially with the empty can lying around. Or they recharged a leak without evacuating and caused non condensables

pecmsg

GBart said:

We have some students working in the field, one told us of a situation he find himself in.

He was sent out with a subcontractor to a AC call at an older office building. Older R-22 system, they go into the office and they note that the ceiling panel under the airhandler is stained and wet and the technician says let's go to the roof and brings gauges and R-22.

They hook up to the unit for that office and find, on a 74F ambient day that the suction pressure is 80PSIG and the head pressure is 350PSIG but the condenser doesn't seem to be moving any heat, the technician says they have to ADD refrigerant and has the apprentice hook up the gauges and start charging in VAPOR........then the compressor seems to die, ( there is an empty R-22 can laying on the roof by the way). He blames the apprentice.

Your thoughts?

Wrong way to train an Apprentice.

SH & SC #'s are required. Get this apprentice with another tech so he can learn properly!

unclejohn

After reading the post many times the only thing I know for sure is that there is a empty drum of R22 on the roof.

Gordy

Where does the sometimes the apprentice Was right come in?

Not following other than the error made by the technician, the technician blaming the apprentice, and the apprentice following his instruction. What year apprentice?

ratio

I read it as the apprentice didn't want to add juice but was told to anyway. Possibly with some verbal abuse.

DZoro

Sounds like they both are at the apprentice level? Yes the true apprentice if he has had any schooling, should have suggested doing "other" before adding refrigerant. Empty jug at a job site, is like a red light, alarms, bells whistles, should have been screaming.

Gordy

I read it as the apprentice did nothing, but follow the leader. There is no wording as to the apprentice making suggestive trouble shooting.

ratio

I inferred from the title and from "...the technician says they have to ADD..." and "He blames the apprentice." I just guessed about the verbal abuse, but I think it was a pretty good guess.

Some guys think that blame goes downhill. It doesn't—it goes uphill. Especially when the apprentices are following orders, but even if they're not. I've taken a$$ chewings for my helper's screwups before, I suppose I'll do it again if I have to. That's the price of responsibility.

nibs

Many years ago while working as a carpenter over heard this conversation;
Apprentice Plumber " how many gallons of water do I need to put up on the roof to get enough pressure for a shower at our cabin?"
Plumber " Oh probably 45 gallons would do"
My mate, another carpenter and I both remained silent with big grins on our dials.

ChrisJ

What did the apprentice say or do that was right?

nibs

Their discussion popped into mind reading through the thread.
Neither the apprentice nor the plumber were paying attention in high school science classes.

ChrisJ

> @nibs said:
> Their discussion popped into mind reading through the thread.
> Neither the apprentice nor the plumber were paying attention in high school science classes.

Plumbers do refrigeration?

nibs

Chrisj, guess my bit of levity did not impress you. Had no intent to offend.

ChrisJ

> @nibs said:
> Chrisj, guess my bit of levity did not impress you. Had no intent to offend.

Calling someone a plumber is certainly not offensive..

I just thought it wasn't correct.

GBart

If you take the temp at the condenser, let's say it's 90, for an older unit add 30, newer add 20 +-, this is definitely an old unit so with 30 we get 120F, convert to temp for the refrigerant you have, in this case R22 that comes out to 256PSIG on my Danfoss slider, that's what the head pressure should be within reason.

The other half is always DO YOU HAVE THE FACTORY SPEC'S???, if you do you use that, if not then you use rule of thumb.

What I didn't explain was the apprentice questioned his findings and actions by asking "are you sure we should add refrigerant?".

He actually said to the apprentice that he thinks there's air in the system.......well hell Johnny you don't add refrigerant, you recover, evacuate, and recharge to the factory spec's IN LIQUID TO THE HIGH SIDE UNDER VACUMM to the lbs and ounces specified in the factory spec's.

ChrisJ

> @GBart said:
> If you take the temp at the condenser, let's say it's 90, for an older unit add 30, newer add 20 +-, this is definitely an old unit so with 30 we get 120F, convert to temp for the refrigerant you have, in this case R22 that comes out to 256PSIG on my Danfoss slider, that's what the head pressure should be within reason.
>
> The other half is always DO YOU HAVE THE FACTORY SPEC'S???, if you do you use that, if not then you use rule of thumb.
>
> What I didn't explain was the apprentice questioned his findings and actions by asking "are you sure we should add refrigerant?".
>
> He actually said to the apprentice that he thinks there's air in the system.......well hell Johnny you don't add refrigerant, you recover, evacuate, and recharge to the factory spec's IN LIQUID TO THE HIGH SIDE UNDER VACUMM to the lbs and ounces specified in the factory spec's.

The "add 20" for a newer unit, is this assuming something in the 13-14 SEER range?

I ask because my own system which is rated 16 SEER usually seems to run around 10+- degrees above ambient.

pecmsg

Condition of the condenser and how much crap in it plays with those #'s also.

GBart

I ask because my own system which is rated 16 SEER usually seems to run around 10+- degrees above ambient.


It doesn't mean there's anything wrong, without the factory spec's you don't know for sure, even if you test SC and SH and get 8 it doesn't mean it's good or bad without the factory spec's, many of the newest variable speed equipment isn't even testable, it's ramping down by the time you would, but 100psig over what it should be is insane, compressors are rated for about 3 - 1 compression or so and made for the refrigerant they will use.

ChrisJ

GBart said:

I ask because my own system which is rated 16 SEER usually seems to run around 10+- degrees above ambient.

It doesn't mean there's anything wrong, without the factory spec's you don't know for sure, even if you test SC and SH and get 8 it doesn't mean it's good or bad without the factory spec's, many of the newest variable speed equipment isn't even testable, it's ramping down by the time you would, but 100psig over what it should be is insane, compressors are rated for about 3 - 1 compression or so and made for the refrigerant they will use.



Yeah,
The highest I've seen my highside run is 320 PSI and that's with 410A.


350 PSI on a 22 system, and adding more gas.....
Like you said, if he suspected NCG, he should've been setting up to recover.

Another common misunderstanding seems to be the TD across the coil. Many assume 20 degrees is normal, but it's highly dependent on both the system and the wet bulb. 15 might be perfectly normal with an unusually high latent load while 22+ may be fine with a low latent load.

GBart

Right without the factory specs you don't know, we have a unit in the school that under certain conditions 22 degrees of superheat is correct.

tim smith

I’m wondering if someone added 410 along the way, that easily could produce those pressures.

GBart

tim smith said:

I’m wondering if someone added 410 along the way, that easily could produce those pressures.

One never knows, but if your pressures are off something may be in there that shouldn't be. 410 goes nuts with even the slightest amount of atmosphere. When I did tech support for Carrier we had calls where guys had new installs that went bad, they changed the TXV's, the evap coils, they had never fully evacuated.