Cold weather and charging

Paul Fredricks_3

We checked out one of our units today that handles a copier room. The unit was definitely low on refrigerant. It was 46° outside with a light rain, 80° inside. we added refrigerant, but are not confident we have the correct charge.



There is a TXV. Subcool was 20°, superheat 60°. Sounds like a bad TXV, but is it, or does the cold and wet have some sort of effect on readings? There is a fan cycling control, but the head pressure never got over 150 so the fan never kicked on.



While we're at it, what is your policy regarding A/C start ups and service calls on residential equipment when it's raining or cold?

Techman

Tuffen up Cupcake

is what I tell everyone that works with me. NOTHING DANGEROUS ! Rain gear makes a nice wind barrier,coveralls,insulated coveralls,gloves ,hats, sweat shirts jackets and such.We do lots of packaged rooftop units,outdoor refrig cond units and some AC for server rooms .It's all part of the service trade. Lots of snow and wind  and cold this past winter.Nothing wrong w/ doing a routine in the cold . Rain and electricity mix pretty well,so thats a no-go .Getting wet is a no-go.Getting cold is a no-go.Getting grumpy is a no-go.Is the TXV superheat adjustable? Is the TXV frozen internally ?

Paul Fredricks_3

I hear ya

One difference is going in and out of someone's house with wet feet and tracking mud. Is there a way to do it? Sure. Booties or taking your boots off each time. Is it worth it? I don't know.



I've done the commercial service thing years ago and I know how that works. Been on snowy or wet and windy roofs myself. No big deal.



But what about temperature. Manufacturers recommend a minimum or 60° to test pressures. What's your feeling on that?



I don't think the TXV is frozen, as in ice inside or wax. But it could be stuck or blocked. And these residential valves are not adjustable.

don_9

cold weather charging

To remove all doubt weigh it in.I know sounds stupid but believe me its not.

One thing to keep in mind,if coils are not clean and you do not have correct airflow across the system then your number will be off any ways.

i have herd and try so many different way from adding 126 degree to outdoor temps to achieve a certain discharge temp six inches from the compressor.to blah,blah.

Most units have a charging chart for the heating performace go with that and return in summer time to check and dail it in.

In your case  the superheat looks excessive but the subcooling seem to fall in place.Could be a restriction or a txv staying ride open or etc,etc.

A quick check would be to look at a heating performace chart that would give you the tr at the indoor coil depending on what outdoor temps you are at.with the second stage heater disconnected.Then again not that reliable if airflow is incorrect.Thank goodness for accumulator.

So back to weighing it in..your thoughts?

Paul Fredricks_3

yes

Weighing in is the best way, but the unit was low, not out. In that case I'd have to recover and start over. Given the numbers I have to believe it's a TXV or restriction issue.



And this is just straight A/C. no heat involved.

John Mills_5

Does sound like a bad TXV

Those miserable things have been failing so fast lately.



We started a new split in an office yesterday. Wrapped the coil with a tarp til the fan stayed on constantly to simulate about an 80° day then looked at superheat. Will return in hot weather to recheck.

Techman

Cold weather

I think if refrigeration units can be started and charged in any weather conditions so can AC units.  With AC its important to have a 72-75* indoor temp  and controlling the head press to be about 95* cond temp will get you really close. Close enough ,so that the customer will not notice  any problems  and then you can go back on a warm day to verify. 95% of the work will be done before the cold weater is gone. Yea, I feel your pain Bro, about  the mud and boots on/off/ on/off .Those few customers can wait until the warm temp arrive.Ac units for server rooms and Fire Dept dispatch office require AC when its 0* outdoors and those units get charged or checked in any ambient, and thats w/ regular compressors or variable speed  compressors.It would be PHYSICALLY IMPOSSIBLE for us to do all the AC routines in the warm weather only.

Paul Fredricks_3

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Yeah, we only do residential. And this time of year it's 62 in the house. No time to warm things up to 72, and the customer doesn't want to waste the oil. tough to do this time of year.



And I'm talking about spring start ups, not installs of service calls. We do a start up, we don't want to go back to recheck. not in the budget.



OK, how about this question on a slightly different note: If I have a 20° TD and my amperage draw is decent, do I need to put the gauges on? A discussion we are having here.

Techman

Mostly

you don't have to.Get ahold of the book {all of 70 pages} by James L Bergmann , HVAC/R Technical Specialist,Testo,Inc..Its called " Air-conditioning Applications Guide - A Measurements Reference for the Advanced Technican " Really good ! I guess I'm supposed to be more Advanced now for having read that book.

EddieG

Good....

Thanks for the info. Looks like a good book. Jim is a great guy. I googled his name and found a printable version.

Techman

Name change

Mr. Bergmann has seemed to have changed the title of his publication.I did not get this information first hand,I don't mind telling you.The new name is " Applications Guide  - AC & Refrigeration  - An Essential Reference For The Advanced Technician "  Also ,Testo, inc. had something to do w/ the name change!

RDSTEAM

cant be weighed in

if its a new start-up you can weigh it in, but your not gonna know how much weight is already in the system when you find it low.

RDSTEAM

amperage draw

wont be a tell all.  your RLA is based on that thing cranking in the summer heat. With low temps, your not putting much of a load on the compressor so your amp draw will be less

don_9

Low on freon

Is that not the issue here?.What good does it do this day in time with freon prices being what they are to juice it up and try getting it dail in?.Heck its a leak and leaks should to be fix.

Find the leak or the problem fix it, evacurate it down to proper microns drop in the charge and know in the long one the customer will be happy you twist their arm into doing the right thing.

If you are going to juice and go please get your customer to sign the invoice knowing the system as a leak and they are aware that it will leak down again and you are not responible for their stupidity.

Its easy money no doubt but the crap you hear out of people a week later after you charge them big bucks to juice and go is not worth it.

Paul Fredricks_3

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Thanks, but this is for spring start ups, not service calls. If we find an issue we would certainly put the gauges on and see what's happening.

Techman

A show of hands,

from those who read the infomation provided by James L, Bergmann !

I did ,again!