Air Conditioner / Heat Pump Refrigerant Overcharge FAQs (2023)

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Overcharged refrigerant in air conditioners & heat pumps: FAQs.

This air conditioning repair article series discusses the the diagnosis and correction of abnormal air conditioner refrigerant line pressures as a means for evaluating the condition of the air conditioner compressor motor, which in turn, is a step in how we evaluate and correct lost or reduced air conditioner cooling capacity.

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Q&A Overcharged Refrigerant in an Air Conditioner, Heat Pump

These questions and answers about overcharged refrigerant in an air conditioner, heat pump, refrigerator, or other HVACR equipment were posted originally at OVER CHARGED of REFRIGERANT, EFFECTS - you will want to review that discussion.

On 2018-08-11 by (mod) - what happens if I put too much charge into a compressor?

You might, depending on other devices being present or absent, send liquid refrigerant into the compressor motor, damaging or destroying it - this is called liquid slugging.

On 2018-08-11 by Md. Abdul Awal

refrigerant r600a charging excess what happen

On 2018-06-28 by (mod) - the unit is not holding temperature

The compressor motor - outdoors? Odd as usually an operating motor warms up enough to be dry.

Is your system otherwise operating normally? Cooling adequately?

On 2018-06-28 by Gregory

the unit is not holding temperature

my central air conditioner compressor is covered in moisture is something wrong

On 2018-04-07 by (mod) - stuck reversing valve

sounds like a stuck reversing valve

On 2018-04-06 by Jose - Why low side on heat pump a/c is hot

Why low side on heat pump a/c is hot

On 2018-03-06 by (mod) -

I would look for

- a blocked condensate drain

- an unusual water or moisture source in the building

On 2018-03-06 by Jose

I have an R22 TXV system, the a/h drain pan has excessive condensation, And keeps dripping water - But does not freeze up.

Please assist. respond to you're assistance is greatly appreciated.

Thanks in advance,


On 2017-12-30 by (mod) -

Possibly low refrigerant o r a failed defrost control

On 2017-12-28 by Andy

Why is my heat pump completely frosted over but still running?

(Video) Refrigerant Overcharge Troubleshooting and Prevention

On 2016-10-26 by Eric Tan

Greetings danjoefriedman, I have a daikin system 3 ftks25dvm coupled to a 3MKS50FSG. I recently have a problem with the FCU blowing warm air (Delta is probably only max 4 degrees c) in the furthest room with a pipe run of approximately 15 m.

I have confirmed the scroll fan and the heat exchanger coil are free from dirt largely to eliminate the possibility of inefficient surface heat transfer.

Upon immediate operation, the air blown is cool but that cease after several minutes. I noticed that the bottom half of the heater exchanger coil is not cold to the touch unlike the top half.

This is true when all 3 FCUs are running or when this particular FCU and another one FCU is operating. However when I operate this FCU alone, air cooling operation is normal and satisfactorily so as to speak.

The bottom half of the heat exchanger in the latter scenario is cold to the touch as well.

Because I was able to repeatedly reproduce this behaviour, I have eliminated the possibility of the thermistor or the PCB malfunctioning.

I have sought advice on another forum and someone mentioned a fault of the EEV controlling evaporator superheat misbehaving.

After some thinking, I am suspecting that a refrigerant leak resulting in an undercharge scenario is causing the EEV to not open causing my symptoms.

To my dismay, I also observed to my horror that the heat exchanger coil to the left side seems corroded and there is some easy free play when a notch should have held the coil in place to the subframe.

I would appreciate your comments about my situation. Thanks

On 2016-09-14 by (mod) - over-filled AC unit caused mold contamination?


this sounds Troublesome to me too. You need an on-site expert who can inspect conditions in your home and tell you what cleanup and repairs are needed. That's not something that I can determine from just your text. Be sure that the expert is paid by and is working for you not the air conditioning company and not a mold cleanup company.

On 2016-09-13 y Tiffany

I had a new AC unit installed last year. The company that installed the unit over filled it. Now I have mold all through my duct work, coming out the vents, it's on flooring, furniture, walls, clothing, ruined under kitchen and master bath sink area. Company doesn't have mold insurance and I'm "Still" waiting for them to say if and when they will fix it all.

Even though the insurance company said they are not covered by mold they sent out an investigator (I feel it's really shady to pay to have him come out if they're not insured for mold) to determine if in fact the mold was caused by the faulty insulation of our new unit and from it being over filled.

The new unit is the same size as our last one. House is 1700 sf and it's a 3ton unit. Could you please (in your professional opinion and experience) shed light on what I can expect? And why this is all going on? It's been a month now with NOTHING being done! I'm scared we are going to have to come out of pocket (it's thousands of dollars at this point) with how shady this all feels!!

On 2016-09-09 by (mod) -

Also see

Choi, J. M., and Yong Chan Kim. "The effects of improper refrigerant charge on the performance of a heat pump with an electronic expansion valve and capillary tube." Energy 27, no. 4 (2002): 391-404.

On 2016-09-09 by (mod) -

Thanks for that important added note, Will.

As you're using EEVs, and some are not operating, you will want to check the wiring between the EEV controllers and the EEVs as well as the location and condition of the sensors, thermistors, or pressure transducers that pass information to the EEV controller. If it were just one EEV I might suspect dirt fouling, but as three of them are off I'd start with wiring and connectors.

Do keep me posted as what you learn will help others.


For other readers, an explanation of expansion valves and electronic expansion valves (EEVs) is at THERMOSTATIC EXPANSION VALVES, REFRIGERANT

On 2016-09-09 by Will

Thanks danjoefriedman. These are electronically controlled ones.

Big temperature difference either side of working valve but the others seem to be moving no refrigerant at all, are not cool to the touch and no frosting. Which is why I wonder now whether the indoor units are the source of my ills. The one that IS working is working great.

On 2016-09-08 by (mod) -

Yes brazing can foul a TXV. Beyond listening to the expansion valve you may be able to measure or feel the temperature difference on the inlet vs outlet sides of the valve; try adjusting the TXV (if yours are adjustable) to see if they free-up.

On 2016-09-08 by Will

(Video) Symptoms of Overcharge

I've installed a new Daikin multi-split system with four indoor units. Deep vacuumed lineset below 100 microns for an hour.

Cracked the R410 valves and fired her up. One zone cools beautifully, but three out of four zones don't cool at all and no frosting evident at condenser end either. I removed and re-weighed gas charge, still no joy.

Tested all gas and liquid thermistors on the condenser and listened to check all expansion valves test operation on system startup

. I am wondering whether brazing heat might have affected indoor units or TXV internals during installation since I find it hard to believe that three linesets could have been blocked on one installation! Any ideas?

On 2016-08-04 by (mod) -

The proper refrigerant charge will be on the data tag for your equipment. Though R22 is obsolete.

On 2016-08-03 by Anonymous

hellow friends i want to know the acurate quantity of r22 gas filling in 2 ton compressor distances is not more than 3mtrs

On 2016-05-04 by (mod) -

Kirk, something is wrong with your equipment or procedure.

On 2016-05-04 by kirk

When putting gauges on the low side too much freon comes out causing freeze burn

On 2016-05-03 by Rick Tormos

My air to air heat pump A/C was recently serviced. Before you could hear the fan only with a low hum sound. Now the system makes a lot of noise that is high pitched. What caused this ? Too much Freon ? Or ??

On 2016-03-07 by (mod) -


You can charge by liquid refrigerant, and most manufacturers describe procedures for doing so.

But the risks are just what you said if charging on the low or gas side but using liquid. When I used liquid refrigerant to charge a system I used a charging cylinder with attached equipment that forced the liquid to convert to gas and charged on the low side.

Using Google Scholar as well as normal web search I did not find any research claiming that there was no compressor damage risk from liquid refrigerant entering the compressor motor at the low side.

I do not know the science that would explain why liquid refrigerant entering a compressor is not at risk of damaging it.

In sum: introducing liquid refrigerant to charge on the high side may avoid trouble, but allowing liquid refigerant to enter the low side of a compressor risks destroying it. A liquid slug of refrigerant entering the piston/cylinder means that when the piston comes up (expecting gas to be compressed by a motor piston) it encounters a non-compressible liquid and bang.

Here is a quote from AutoAC forum

When the system has no charge and you've pulled a vacuum on it, you can dump (turn the can upside down) a can of r134a into the high side port using a manifold guage set and having the engine off. It'll pull in at least 12oz easily and it's a quick way to get the system a small charge.

When charging it up the rest of the way, you have to have the motor running, the a/c on max and the can kept upright putting into the low side port.

With the can upright, the r134a is pulled in as a gas. You never want to tip the can upside down and pump pure liquid into the low side.
The charging of a refrigerant as a liquid into a non running/non compressor activated system,either low or high side depends more on where the service ports are located.

If charging into an accumulator, it really makes not difference. However, if charging into a a service port that is near or on the compressor could have serious effects on the compressor at start up.

What can confuse many of us is that manufacturers often describe charging with liquid refrigerant on the LOW side - but you have to READ the instructions. For example Carrier describes this process for a split system A/C unit but you have to notice that you are charging with liquid through a charging cylinder that will be sure that only gas actually enters the low side into the compressor.


On 2016-03-07 by Dobie Lawrence

I'm working for an A/C heat and refrigeration company. The tech I'm working with charges units by liquid only.

I have told him that I was taught to charge by gas not liquid that it will cause slugging and burn the compressor. He said I'm nuts and that every tech charges by liquid that it's faster and the piston or metering device will flash it off. I am going nuts cause there is no piston or metering device from the charging ports to the compressor.

Please give me a straight foward answer with data back up so that I can inform him. Thank you for your time and effort.

On 2015-10-11 by Metoyou

I have a Lenox heat pump system with a carrier coil. When properly charged for cooling and ran in heat mode the high pressure pop off is popping open. What is causing this problem?

On 2015-08-07 by (mod) -

(Video) Air conditioning system that was overcharged


In the links above, please see REFRIGERANT HIGH HEAD PRESSURE DIAGNOSIS at

for a detailed answer to your question and an expansion of our discussion of the causes of high compressor head pressure.

On 2015-08-07 by (mod) -

Incidentally experts say we need to look at super and sub cooling to diagnose these problems, but a quick check of temperatures across the filter drier can be handy. If the filter drier is clogged you'll see a temp drop across its inlet to outlet ends. Make this check at the start of an on-cycle.

On 2015-08-06 by Tim Nordyke

The tech offers nothing......

He is sticking to his claim it is all the condensers fault.

When the system ran just before it gave up the ghost, there was no ice or even condensation on or around the TXV (found correct name).

What has me wondering is how did I get a high head pressure (faulty switch?) when the pressures were at 100 lbs. just before they evacuated the system, and the amb. temp. was 95 degrees.

On 2015-08-06 by (mod) -

Maybe so Tim. I like to assume just one snafu at a time:

Certainly if they added freon and didn't fix the leak you'd be low on freon again.

Low freon can ice the coil reducing or stopping actual cooling and it might ice the TEV causing it to block all refrigerant flow.

That MIGHT give a high head pressure.

The problem would continue until so much refrigerant has been lost that the TEV no longer ices (and the coil no longer cools).

What does your service manager offer?

On 2015-08-06 by Tim Nordyke

Well that's why I'm coming here.
The clueless tech only used an ammeter to check current draw, said that 6 degree drop from intake to out wasn't the best, but was not a solid indicator of a problem.

I learned last night that the system had to be recharged 7 years ago and all they did was add freon.

o I'm thinking that the prior problem contaminated the system, the freon was leaking out, the TEV was clogged so it couldn't shut off flow to the evap coil, and since the return line wasn't cold enough to cool the compressor, it overheated and locked up.
Had tech 1 hooked up his gauges when the system was still running he would have caught the pressure issue and saved my system.

On 2015-08-06 by Tim nordyke

I had a lennox system that had a very weird set of symptoms. It was an r22 3ton that was around 20 yrs old.
In the course of 10 days the system kept popping the high head pressure switch (8 times total) yet the temp difference between intake and output (inside) was only 6 degrees.

The AC tech from the home warranty co. blamed it all on a 20% damage area to the condenser from corrosion, and his test set was a clamp on amp meter.

He never once connected gauges to check high/low pressures.
10 days after first incident, the compressor locked up and gave up the ghost.

When the new system was being brought in, the installer noted the pressure in the system (both sides) was only at 100# and the ambient temp was 95 degrees (per the gauges), the installers claim that the old system did not have enough refrigerant, and that the TEV was clogged/jammed.

Does this sound right?? Too little freon, clogged TEV, 6 degree drop from intake to output, and still pop high head pressure?

On 2015-06-24 by (mod) -

Pat this sounds like a control or blower assembly issue or maybe a coil icing problem. I'd give your service tech a call.

On 2015-06-23 by Pat

My home a/c works exceptionally well at times. Then all of a sudden it feels like it is sucking warm air mixed with the cold air for a little while, causing me to feel ill. (and I'm not having a hot-flash, because my 10 year old feels it too) Then, it starts blowing cold again. Please help me! What is the problem? Thank you in advance.

On 2015-06-07 by (mod) -

Laura freezing up is likely to be an undercharge.

Watch out: when your system has lost refrigerant the proper repair is to find and fix the leak rather than to just keep adding refrigerant.

Watch out also for service companies who just deliver an unknown quantity of refrigerant, take your money, and leave.

(Video) [2019] How to Diagnose a Refrigerant Overcharge (On a Res A/C)

On 2015-06-07 by (mod) -

Re-posting from mobile comment

AUTHOR:laura bass (no email)

COMMENT:My air unit was freezing up and tech came to recharge it now it doesnt blow cool air at all. Could he have overcharged it and can that be undone?


(Sept 6, 2014) Anonymous said:
so very hard work . but this is my course R.A.C

(Apr 28, 2015) Robert Muela said:
my low side is 10 my hi side is 200 why


Robert, see and then also see REFRIGERANT DIAGNOSTIC FAQS. We expect the low side to be much lower pressure than the high side when the compressor is running.


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