Low suction high liquid pressure

[Dadbod]

So I’m a tech coming in after someone’s install. I was called out to look at a Lennox unit short cycling. It’s becoming the largest headache I’ve had to deal with in awhile at this point I have reclaimed and vacuumed down the whole system and added refrigerant but when the compressor kicks on the suction side drops quick and the liquid shoots up to well over 300 and then shuts off. I don’t want to overcharge the system. But I can’t figure out what the heck is the problem. I’m a bit newer only 7 years in and my master bailed before I got a full helpful training on ac. So if this is a stupid question I understand but I’ve never encountered this before. I need help.

[CEAS-AC-TECH]

Dont take this the wrong way, but Bro...
7 years? You got a restriction. How long have you been a tech?

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[2sac]

Instead of giving you the answer, think about what is happening in the refrigeration cycle and what is supposed to happen. Start with what are the causes of low suction pressure.

[Dadbod]

I know, I know I only just started really doing service by myself for the last 2 years. Thank you, thank you.

[FreeThrowGuy]

I know, I know I only just started really doing service by myself for the last 2 years. Thank you, thank you.

Are the service valves open? Lol

Fixed orifice or TXV?

Which way is your filter drier arrow pointing?

I'd start with the basics

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[DeputyDawg605]

Sounds like a restriction.
Look at the TXV or piston which ever you have.
Make sure service valve are open.
Just slow down., think it out, and go through the refrigerant cycle checking every component that could restrict the flow.

[Achso017]

Nvm. Didn’t read post properly. Sounds like a restriction like these guys said.

At what pressure does it shut off? What is well over 300?

[GeorgeKM]

Installers can be thoughtless at times. If you've tried to find it by temperature, put a piercing valve on the liquid line, if it's still 300psi check down stream what the installers have done. If it's low check what they did on the condenser side, then pump it down and fix the little hole.
Installers rule of thumb, little solder good lots better. Little heat good lots better.

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[VTP99]

300 / R410a ?

[TechmanTerry]

You came along after someones install? So, I'm guessing r410a? What was room temp and ambient? What does "well over 300 psi" mean?

[kidhudi]

410a i am assuming you have a TXV.

check for a temp drop across the liquid line filter/dryer also a temp drop from where the liquid line leave the condensing unit to where it enters the evap.
check for a clogged screen at the txv if there is one there. also could just be a bad txv. like they said. just think about it without freaking out it will come to you.

[gkboghdady]

300 psig for liquid line R 410A that's Not bad .. and how low is your suction line pressure ?? need Number .. you need to measure superheat and subcooling to make sure that there is a liquid line restriction .. if there is a liquid line restriction Evaporator coil will be starving for refrigerant and you're going to get high superheat on the other side refrigerant will be spending longer time in the condenser coil and releasing more heat and that leads to high subcooling too

[Olivero]

If you weighed in the charge and it's short cycling, most likely it's a restriction. Could be the drier, could be the TXV or piston or whatever you have.

Sounds like a restriction though.

[oldguy1949]

I had an installer swedge a 3/4 suction so it would fit over a MH evaporator suction fitting and didn't cut out the factory copper plug. Got the dreaded call after quitting time so I go and it took me about 30 minutes to finally figure out where the restriction was. Tested usual suspects & even removed all the insultube looking for kink, luckily only about 12 ft.
This was the iceing on the cake, sent him packing the next morning.

[Glennhvac]

One I found this summer. First time it didn't run perfect for 8 years. Solder broke loose between dryer and coil.
restriction by Glenn Hanson, on Flickr