Ways to lose refrigerant

Toad

Do folks have any thoughts on the frequently heard “your refrigerant reading is a bit low”? (During annual preventive maintenance residential AC checks.) Absent a leak, aren’t these closed systems that shouldn’t require “topping off”?  Is there any possibility, that similar to how we sometimes lose too much air when checking tire pressure, it was due to a mishap during the measuring process that lost the refrigerant, or does it not work that way?
Just trying to get the experts’ view on how often it is due to a bad reading when level is actually ok, losing pressure due to the reading itself, a leak (which I would think would need to be identified and addressed before just adding more refrigerant, or (and hopefully this is not often the case) unnecessary work. Thanks. 

HVACNUT

Assuming the original charge is correct and there are no condensables, it's a closed system and should never need additional refrigerant. 
Nobody should be  adding refrigerant and then just walk away. The problem should be found and repaired. Leak seal is an option but not a guarantee. 

pecmsg

Salesmen trying to make extra $’s. 

You can’t tell refrigerant level with just gauges, the corresponding temperatures need to be takin and super heat or sub cooling readings analyzed. 

mattmia2

Should you be connecting a manifold set at all during routine service unless you have reason to suspect it is not performing at the correct capacity?

ratio

I think that, barring a leak, that's more likely due to different tech's idea of 'properly charged'.

Some refrigerant does escape when nippling on & off the system too, & that will add up over time, especially with a fixed meeting device where 'properly charged' is a noticably small window.

I mainly do new work, & a factory-charged unit doesn't get gauges on it if it's performing adequately. I've seen how much even a 36" hoses' worth of refrigerant can change performance.

EBEBRATT-Ed

A properly charged system should be leak free. No need to put gauges on a system unless you suspect a refrigerant system problem.

@HVACNUT is correct you shouldn't add gas to a leaking system. Putting gas in a unit to get them through the night may be acceptable (especially food service or hospital equipment) but not constantly refilling a unit without fixing or changing it. Way to much gas and go going on

kevinj_4

And I have found many plugged coils, dirty blowers, etc.

All can mimic a low charge with reduced air flow.

ChrisJ

mattmia2 said:

Should you be connecting a manifold set at all during routine service unless you have reason to suspect it is not performing at the correct capacity?

I'd be pissed if someone hooked gauges up to my system if it's working correctly.
I expect zero refrigerant loss unless there's a leak and if there's a leak I want it fixed. Blend refrigerants such as R410A do very poorly when the system is leaking and IMO the only proper way to treat it is recover the entire charge and fill fresh after the leak is repaired.


But that's me.

SuperTech

Wireless probes are a different story from gauges.  They hold almost no refrigerant. Still, there are other ways of verifying that the system is functioning adequately. 

Toad

Thanks for all of your responses. Very helpful and consistent with what I had assumed. 

One follow-up - at this point my concern is whether it is actually low and if so, can it damage the equipment in any way. Is it safe for me to assume that if it is a Spacepak/Unico-type system and the house seems to be cooling as it always has and I can measure a 15-20 degree differential between air temp at the intake and the outlets, I’m probably ok and should adhere to  “if it seems to be working, don’t go looking for problems”?

Thanks again everyone. 

pecmsg

Over or Under charge Can and Does shorten the life of the compressor. 

ChrisJ

Toad said:

Thanks for all of your responses. Very helpful and consistent with what I had assumed. 

One follow-up - at this point my concern is whether it is actually low and if so, can it damage the equipment in any way. Is it safe for me to assume that if it is a Spacepak/Unico-type system and the house seems to be cooling as it always has and I can measure a 15-20 degree differential between air temp at the intake and the outlets, I’m probably ok and should adhere to  “if it seems to be working, don’t go looking for problems”?

Thanks again everyone. 

The temperature drop depends on a lot of things. Humidity, indoor and outdoor temperatures etc.

If the humidity in the space is reasonably low I would expect close to a 20 degree drop. If the humidity is on the low side some systems will do over 20, even 25 degrees. But with high humidity and it being hot outside 15 degrees could be good too.

A quick way I check systems I'm around that are running normally is feel the lineset and the air leaving the condenser. If it's hot outside and the air leaving the condenser is fairly hot, liquid line is close to ambient and the liquid line feels ice cold, the system is working pretty damn good in my opinion. This may or may not work on inverter type systems.


I'm not a contractor, nor do I play one on tv.