It took me a while to realize the behavior of a "fixed" metering device is dynamic due to changes in the high side pressure. On a hot day when there's more load on the system pressures will go up and more refrigerant will go through the fixed metering device. In the experiment you ran, the high side pressure dropped, which lowered the amount of refrigerant going through the piston which helped the system stabilize in the low airflow condition.

@measureQuick

16 күн бұрын

@@arthurhartwick7974 100% correct! I was thinking earlier I wish I had said that in the video.

This software saves me hours of time doing math and guessing. It usually gets it right on the first or second fault. It has helped me immensely. Usually it describes the exact problem I I’m thinking and sometimes it surprises me. Some people think this is a shortcut, yes and no. It teaches you too. I spend less time on a service call often. Thanks for this!

Can we please get a subscription service for the app instead of buying qbits!

@joeshearer1247

16 күн бұрын

Yes please let us have a subscription level to pay to be allowed to take screenshots again

I appreciate your contribution to moving the industry forward Jim. The MQ app is fantastic, recently it keeps saying the “seer rating is not possible”. In the real world the seer rating is almost never possible.

@measureQuick

15 күн бұрын

Usually what happens in that case is the air handler and condenser amps are swapped.

Love these scenario training videos. Thanks Jim! Looking good too 😎

Twice in a 40-year career on water cooled, R22, TXV systems with low airflow I witnessed such severe flooding that the discharge lines were heavily frosted. The first one was a 100-ton Carrier system, the second was a 5-ton Chrysler Airtemp system. The compressors survived somehow. I swear that this is true. I never saw anything close to that on air to air systems.

@measureQuick

15 күн бұрын

I’ve seen a hot gas line, frost, but never a discharge line. Sometimes the refrigerant would back up in the hot gas line and has the system ran it would’ve evaporate out and cause the frosting. We had to put a check valve on the packed tee on the expansion valve to stop it.

….got a little bit out of this video? No, but a whole lot. Always looking for your videos, and always impressed how well it is presented. Beautiful!! Thank you Jim. I’m wrestling with low SC and low SH. Suspecting an oversized piston. Perhaps I should increase the blower speed?

@robertcherry4971

10 күн бұрын

What are your saturation temperatures with the low superheat and low subcooling? Return temp Wet bulb and dry bulb? Supply temp dry bulb? Outdoor ambient? Thank You!!

Great info. to know. Thank you, Jim.

Awesome video

Wicked good video Thank you

If you increase airflow and the charge boils off quickly, why is there no superheat? Seems like you wind up with all vapor so no risk of liquid to the compressor.

@measureQuick

16 күн бұрын

@@realSamAndrew 0 superheat means liquid flooding. The refrigerant boils so quickly that it carries the liquid with it. The rapid boiling basically pushes the liquid out of the evaporator.

@HVACRTECH-83

9 күн бұрын

Well I was also wondering about this too. How do you know for sure it was flooding just because it says zero sh? I stopped the video when you put door on and asked what we thought was gunna happen,and thought about it and I predicted it would shoot strait to zero but for a different reason than you explained. So I thought it would instantly start raising in sat/ and pressure,which it did, but I thought the suction line would take 20 or 30 secs to start reading correctly. So if the vapor line was still reading around 28 and sat went up to 31 you'd be about 3 deg subcooled and since there's no negative sh it just says 0. Same exact thing as when the sh went up briefly when you first took the door off,then started coming down once pipe cooled down. Without a clear pipe there's no way to know unless you hear the compressor actually flood. Rite?

@measureQuick

9 күн бұрын

@@HVACRTECH-83 I know for sure that it was flooding because when I was an instructor I put sight glasses in suction line and performed the same experiment. I have seen it. Subcooling cannot be negative. If it displays that way it is an error in the calculation.

But what if we have a dirty condenser coil and low indoor air flow? In that case we would flood the compressor I think. What do you think? Thanks.

@measureQuick

15 күн бұрын

@@user-kn7cp4me8n it likely still would not as your not moving enough heat. The low side has to absorb heat to reject it on the high side.