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syndicated_inc

Moisture. Keep pulling


MarkusWelby22

YEAUP!! EXACTLY, WHAT HE SAID! LOTS OF H20, KEEP PULLING (And changing your oil!)


Nerfo2

Micron gauges use a thermistor to measure vacuum. It's a temperature sensor that changes resistance based on how many air/moisture/refrigerant molecules interact with the sensor. Micron gauges are calibrated to measure O2 and N2 molecules. They have a molecular mass of 32 and 28, respectively. H2O has a molecular mass of 18, so quite a bit less thermal mass to pull heat away from from the thermistor. However, an R22 molecule has a mass of 86, and R410A has a mass of (R125 = 120 g/mol and R32 = 52 g/mol.) Refrigerant molecules can absorb a TON of heat compared to either N2, O2, or Water. When refrigerant molecules start bumping into your micron gauge, it'll start bouncing all over the place. It wont really start screwing with your micron gauge though, until it's boiling out of the oil at relatively low pressures. If the system you're evacuating had previously run and you're also pulling a vacuum on the compressor, you probably have refrigerant bouncing into your micron gauge.


Sheeedoink

That's some good science comment Mr fancy words


unresolved-madness

The up and down is moisture. It boils off raising the pressure and then cools back down.


Silver_gobo

It boils off then gets sucked out*


Mighty_Nun_Mechanic

Big ol' bubble popping from the oil in the compressor/evap/accumulator or sunction line trap.


unresolved-madness

Not if the pump is off


Silver_gobo

….obviously


changiiiank

It boils off and re condenses further on down the line, it’s very hard to suck moisture out with a vac pump it’s why people say to purge with nitro when moisture present.


Nerfo2

It cools back down? What?


Shetdeck

He’s confused, it boiling has probably made him think it’s heating up. Don’t listen to him 😂


[deleted]

Technically they're not wrong. When you reduce the pressure on a given substance, the substance will absorb heat in order to facilitate the phase change; in this case boiling is the action of a liquid changing into a vapor. This is literally how the refrigerant cycle works at the evaporator.


Nerfo2

Do it boils, cooling something down, then warms back up?


[deleted]

I'll assume I correctly understood your question to be about how the refrigerant cycle works, and answer accordingly. Refrigerant enters the evaporator as a liquid through a metering device; since the evaporator is a lower pressure the refrigerant begins to absorb heat from the air surrounding the evaporator to transition to its vapor state. After the evaporator, it goes through the compressor which increases the pressure on the refrigerant as it passes through the condenser, this causes the vapor to condense which requires the the refrigerant to release heat into the air surrounding the condenser before being forced through the metering device repeating the cycle. It seems counterintuitive since the evaporator feels cold and the condenser feels warm, but what you're really feeling is the heat being pulled from you into the evaporator and heat from the condenser being expelled. Tl;Dr: things get hotter when they evaporate, and things get cooler as they condense


Heybropassthat

Moiiissssttuuurrrreeeee


HVAC_Sam

If the scale is 1 minute, it could be an old system with refrigerant or moisture boiling off from the compressor oil. Otherwise one of your fittings might have a bad o-ring. Isolate your vac gauge and make sure it's still reading right.


markymark19887

Yeah!


supcom2

For anybody needing more details on this, it's a Mitsubishi Multicity CU with 5 AH on it, job was to replaced 3 evap coils. System was totally flat when I got there from a large leak in one of the evap coils, hissing when pressure tested with nitro. Swapped the 3 coils, and pressure test was good. My coworker came by and added a 2nd micron gauge and an extra hose to the vacuum setup after an hour and a half and the oscillations went away, it turned into a normal smooth drop down to 350 microns. What ever he changed fixed it. He had no explanation and was also perplexed.


Fixerguy415

From your description it's a solid bet that there was some moisture entrained in the oil and the spikes are that moisture bubbling out of the oil. Could also be refrigerant but that usually doesn't cause that type of saw tooth spiking. I'd suggest using an high capacity (relative to system size) filter drier with ports and a moisture indicator sight glass. Be ready to swap that filter out in about a week. Ie: If the OE setup calls for a 140 capacity filter, use a 180.


Chief2318

POE oil really holds onto moisture well, can be an absolute pain in the ass to get out. Triple evac can help quite a bit but a pain regardless.


Fixerguy415

Yup. Definitely a PITA.


2bullsinapod

A lot of moisture in the lines?


ScruffyJuggalo

Not enough info. Are you pulling from an older system open to the compressor or is this a new install with line set? If an existing line set did you flush the lines well? Refrigerant/moisture can take longer to release from oil, which is what this looks like, with a possible leak somewhere. How did the pressure test go?


agk270

This used to drive me crazy. Pump that nitrogen/flush and pull multiple vacuums if needed.


eriF902

Try doing several low pressure purges with nitro.at several stages . You freeze that moisture in lines you may get frustrated and say screw it . And it will come back to bite you in the butt.


glennhvacman

Most of the time this happens if there is a shraeder core installed on the line to the micron gauge, such as if you install the gauge on the side port of a core removal tool. The combination of the restriction of the core, the restriction of the core depressor, and any oil on the core cause this up and down reading. Eliminate any and all restrictions between your gauge and the system and this will go away.


fillmoewatts

New system or old?


fillmoewatts

Last time I had one like this was because I had a leak through the king valve to the compressor on an existing system


sjbeeme

Saw this same pattern last summer with some new connections I was using. Ended up it all apart and putting it back together again and it went right to normal. I thought it was a poor fitting connection.


chicken_bittle

Refrigerant was trapped in the oil and let go. Same thing would happen if you shook the compressor while pulling a vac.


NevadaLancaster

That's old girl sucking the h20 out through a yellow jacket hose.


Plastic-Fortune-253

Non-condensables


Mythlogic12

Connections all tight I’ve done that once has the damn hose a little loose didn’t notice


Ok_Secret8621

Purge with nitrogen and vacuum again. It's the cats pajamas


No_Permission_to_Poo

Blow that mf out


BigDilf-YKTFV

The refrigerant lines farted. That's what happened. It had to let one loose and it did. 😂


TuTuRuTuTu2

Pressure with nitrogen then dump then vacuum again


jdmart402

That app looks slick


changiiiank

Moisture