700 PSI on start up

charliechicago

I have a 410A york microchannel condenser that on start up instantly goes up to 700 psi. It is not overcharged because I am the only one who has worked on this unit, did not do install but system has not been touched since. Coil is not dirty, as I chemically cleaned it on the spot. I'm thinking its the txv? Is it possible one of the circuits in the condenser is blocked, its microchannel, and that could cause the pressure? How could I test txv vs blockage. Thank you! Michael.

EdTheHeaterMan

Never needed one before so I'm not sure, but infrared camera technology may help show a blockage.

Off-Topic: but related to infrared camera use: The only time I wanted to use an infrared camera on the job was to see if there was overheating under a boiler on a wooden floor, I called the Fire Department and asked them to look at the structure with the infrared camera they just purchased. (read in the local paper about their new firefighting tool) Confirmed my suspicion of a smoldering wood floor under a newly installed boiler. With the help of the several strong firefighters I cut the boiler out and they lifted the boiler out of the way so they could mitigate the smoldering wooden floor members. The old boiler was wet base approved for combustible floor. The replacement boiler was not approved for use on combustible floor.

Back to blockage topic. With new cellphone apps and attachments, infrared photography is much more affordable today. Look at the coil for temperature changes in the coil you are having a problem with. The colors should change evenly across each circuit. If there are inconsistencies in the color pattern, you will see if there are blockages

Ironman

It COULD be a bad TXV if it's closed and the compressor is trying to pump the entire charge into the condenser. They only way to properly diagnose a TXV is with the system running.

What's your suction pressure?

ChrisJ

charliechicago said:

I have a 410A york microchannel condenser that on start up instantly goes up to 700 psi. It is not overcharged because I am the only one who has worked on this unit, did not do install but system has not been touched since. Coil is not dirty, as I chemically cleaned it on the spot. I'm thinking its the txv? Is it possible one of the circuits in the condenser is blocked, its microchannel, and that could cause the pressure? How could I test txv vs blockage. Thank you! Michael.

What's the suction side doing during this?
I assume dropping really low? Does it give you time to feel the piping to see where it's warm / hot vs cold?

HVACNUT

> @Ironman said:
> It COULD be a bad TXV if it's closed and the compressor is trying to pump the entire charge into the condenser. They only way to properly diagnose a TXV is with the system running.
>
> What's your suction pressure?


Yeah that. Straight A/C, not a heat pump?
Do the pressures equalize when its off?
Clogged suction or liquid line drier?

JUGHNE

IIRC most units come with enough charge for 15' lineset.
If much longer then MC coil maybe not hold it all.
Does TXV get cold at all.

mattmia2

My AC did something similar when it was first installed 20 years ago, they ended up replacing the TXV(after recovering the charge then using r-22 to fill their leaking tire...). It appears what really happened was that when they opened the service valves it pulled a slug of oil out of the condenser and in to the TXV.

JUGHNE

When it goes up to 700, does it drop eventually?
If so then the liquid must be squeaking thru the TXV.
Plugged LLFD might do it also.

I had this happen, but it would just pump down into copper tube condenser coil and go off on LP switch. Txv was nearly plugged....maybe from Copeland compressor processing oil that gave some problems about 7 to 10 years ago.

charliechicago

Thanks for the response!
I don’t think it’s the FD because it’s in the condensing unit and my hoses are downstream and I would presume I would see a lower pressure there. The suction pressure does START to drop, it’s at about 125 psi, which I think is standing pressure, it’s in a basement, but then it shuts off on high pressure. I could override it but am afraid of too high a pressure? Not sure if that’s being too overprotective because if the fan goes and there’s no pressure switch you have the same situation, which happens all the time. It’s not a heat pump. The head pressure drops when it shuts off but the suction pressure stays put, I think around standing pressure ,125 psi
Thanks, Michael.

ratio

700 is way too high & points at a blockage I believe. With that kind of pressure, I'd be looking for a plug left in the lineset or a valve closed, but it sounds like this is an existing install?

Was N₂ used during installation? Might be scale somewhere, but I'd kinda expect that to be in the filter/dryer rather than the TXV.

There was that whole oil escapade that @JUGHNE mentioned, too… I got bit by that one, took Trane's factory guy to figure it out; & he had to call tech support!

JUGHNE

In my case the TXV was not available so I was given a new indoor coil under warranty.

HVACNUT

Looks like you're going to have to recover and investigate.

pecmsg

You Do Not "Chemically Clean" a Micro Channel!

What's the suction? Throttle it back, if it settles down its Overcharged!

Matt_67

I’m guessing your gauges are on the liquid line. If that’s the case a condenser blockage is not the cause. Is the condenser fan spinning the right way? Drawing proper amps? Sometimes a failed capacitor will allow a motor to start backwards.

EBEBRATT-Ed

If overcharged the liquid line will be cooler than normal (too much subcooling) Find the restriction by using a thermometer,

Get temp in and out of the condenser, across drier also check subcooling if high then that adds to the restricted high side theory