Checking a system with the wrong sized piston!

In this video we come back to a recent call where I found high head pressures and a 0 superheat. Today im there to remove the piston and check it for a obstruction. When I pull the piston and check the piston size chart, it becomes a different situation.

[vincentfranze]

Thanks for the video I enjoyed it. I started in the HVAC field in 1978 at 18 years old and am still doing it although I am now a service manager in an office. I conclude that the 57 piston was indeed too small as proven by the 65 piston being listed in the Goodman piston chart as the correct one for the 3 ton condensing unit. That one was easy. I conclude that the system was overcharged because the 57 piston would not allow for enough refrigerant flow for proper cooling and overcharging will force more refrigerant into the evap. coil and "get more cooling" even to the point of flooding back to the compressor. Note that the superheat was zero which indicates flooding in this case. The high subcooling and high head pressure readings are both indicative overcharge in this case. As for the restriction talk, although high subcooling may indicate a restriction in some cases, you will also have high superheat and not low superheat as long as the refrigerant charge was correct and of course proper airflow through the evap. coil. Also, a restriction in itself with proper charge and proper airflow through the condenser coil will not significantly raise the head pressure and in this case the high head pressure was another clue of the overcharge.

[realSamAndrew]

Looking at some of the other comments and noticed the same thing as what they noticed. First, a .065 is larger than .057, so either you read the number wrong or the new one should have been even larger. Second, if there was a restriction, the evap would be starved and you would be at freezing or below and superheat would be high. You had a flooded evap so it was overcharged or piston too large, which if true means like the other guy said, may have been .087.

[soloch]

I had the same problem this week with a R 22 system good man air handler the installer left the 09 piston in I removed the 0.9 Piston and replaced it with a 65 and it’s working great, thank you for the great videos keep them coming

[blackericdenice]

Your video helped me fix my problem. I installed a Goodman 2 ton condenser onto a Rheem 2 ton n-coil with a txv. My low side pressure was really high and it was not cooling. I removed the txv and installed a .57 piston. The low side pressure came down and after adding refrigerant. It’s cooling better.

[Alienspecies]

I had this same experience! The system was only giving me a 10 degree delta T....we ended up changing out the piston and that bad Larry was cooling with a nice 20 degree delta T. I also changed the filter dryer. Systems been running beautifully for the last two summers.

[robertcherry]

A restriction would cause low pressures unless it was restricted and overcharged. Which they often are previous tech saw low pressures from restriction and added refrigerant. Also with a restriction superheat and sub cooling will be high. The symptoms your unit is showing is overfeeding metering device.

[drewf]

HOLY CHIT...couldn't figure out why my high pressure line kept tripping when above 95 degrees outside! Thank you! Mismatched piston.

[rickl]

Thanks for this video, you did a great job! However, to me those readings you're getting aren't symptomatic of too large of a metering piston. If you had too large of a piston the superheat would be too low like it is, but your sub-cooling would also be too low; the liquid refrigerant would be flowing too fast out of the liquid line and never have a chance to sit and cool long enough to give you the proper amount of sub-cooling. I think what you have here is too small of a metering piston installed AND a gross overcharge of refrigerant or a very dirty evaporator, or secondary heat exchanger or air filter.

[DoctorSleep_]

Whether the piston was being overfed or not, those pressures indicated the system was overcharged. Low superheat and high subcool is the major indicator, as well as the normal to high suction. Retrictions are indicated by a high superheat and high subcool, with a low suction pressure.

[mikel.]

I watched this video because i thought I had the same problem. It all started with a hissing (rushing) sound near the piston that would come and go as the unit ran. I'm an auto mechanic so the first thing I thought was low refrigerant charge because that is what some car systems do when low. I checked every inch of the system and no leak. The unit had ran fine since it was installed 10 years prior. A couple of years ago during a storm we lost one leg of our power and the condensing unit was making a horrible growl so I turned it off until power was restored. This was the clue I needed. One morning the condensing unit started the growl, no storm or power outage. I turned it off. Hooked up some gauges and they were fluctuating just like in this video. So I thought clogged piston. The piston size was written on the case with the bag taped to the unit as well. An it matched the Goodman chart. I checked power across the contactor and had 112v on one side, 83v on the other and 120v and 120v coming in. I removed the contactor and sure enough the contacts were cooked. Luckily there is an AC supplier close by and I bought a new contactor and capacitor. Pressures are now stable and no more hissing sound. I was surprised,

[hediervarelamedina]

The video is good but as far as I know the super heat within a normal working range should be between 8 and 16 degrees Fahrengeith. and the Coollin sub from 8 to 12 degrees. Other than that, the video is very good. It has very good tools to diagnose AC equipment. Blessings .

[briancarlisi]

New to your channel. First time seeing an oversized piston so this was very helpful. Not sure where you are at but those houses looked like the ones near me in Canton Ga. Thanks again. Brian

[android]

Man that vacuum pump jumper thing would be a life saver for me and so will the rest of the video

[floridasaltlife]

Great video and great content, very educational and insightful of real world. Big Thanks...

[mp]

I’d of cleaned the outdoor coil, checked airflow inside and recovered some refrigerant… even if it is the wrong size piston, it’s definitely overcharged

[jericosha]

Thanks for sharing this. Not something I really consider, so it's good to have this in my back pocket.

[keithmckay]

I had this problem today. I replaced a leaking coil with a cap tube replaced it with a coil with a piston instead. Installed a 0.068 piston for a 2.5 ton outdoor unit r22. And it was doing this sorta. its working decently had a 19/20 ish TD across the coil target superheat was 16 but It was maintaining 8 to 5 degrees of system superheat also added in a filter drier because system originally did not have one but I can't seem to get the super heat up. I suspect low airflow but its a super old system with old wood box style duct work. Even went through the house and made sure all the registers were open for proper airflow it really has me scratching my head.

[gunnervines]

Make more videos! One of the few worth watching

[chrisnorris]

That jumper cord u use for the vacuum pump we call them suicide cords or power thieves

[brnmcc]

That .057 orifice is the size for a 2 ton R410A system. Why would a 3 ton ADP coil come with a .057 in it? They messed up at the factory, or someone changed it. Should have been the pretty close piston right from the factory in the ADP coil.