Q&A about refrigerant charge quantity for air conditioners & heat pumps. Set #2.

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.

We explain how overcharging or undercharging of refrigerant in an air conditioner or heat pump is detected and we list the effects of overcharged or undercharged refrigerant.

We discuss how to diagnose refrigerant pressure problems; how to determine the proper refrigerant charge quantity.

Page top photo: refrigerant high side and low side refrigerant pressure test gauge set used by the author: Daniel Friedman.

Q&#2 A/C or Heat Pump Refrigerant Pressures

These questions & answers about refrigerant pressures & pressure charts or pressure measurements were posted originally

at REFRIGERANT PRESSURE READINGS & CHARTS - home. Be sure to review that article.

Measuring the refrigerant pressure in air conditioning, heat pump or other refrigerant systems can diagnose a range of operating problems including a refrigerant leak, over charging or under charging.

Can I bypass a low pressure switch that turns off my A/C system?

How can I start HVAC if low pressure switch does not allow it to start? - by Nessisso

Reply by (mod) - Don't: if low pressure switch won't let the A/C start fix the problem

You may need to repair or replace a refrigerant metering device like a thermostatic expansion valve or capillary tube.

Watch out: You should not force the system to run because you're a subverting a safety device. Forcing it to run could be dangerous.

Why won't my car A/C system not cool enough?

I have an '07 Dodge Ram. The ac is cooling but not as cold as it should be. I have a low pressure reading of 70-75psi and a high pressure reading of 80-90 psi and the high pressure line is icing f up from the firewall to about halfway to the front of the truck. What might be the problem? My email address is henryr79@att.net. On 2019-04-29 by Henry

Reply by (mod) -

Often when there's icing it's due to low refrigerant; second most common cause: improperly-functioning refrigerant metering device.

But unlike building air conditioning and heat pump systems, it is common to lose refrigerant from an automotive air conditioner if the A/C system is not used for many months.

A home or building air conditioner uses a hermetically sealed compressor whose moving parts are all enclosed. But in contrast, an automotive air conditioner compressor, because its driven by an external pulley and fan belt, risks refrigerant leakage around the pulley shaft bearing.

Watch out: OPINION: it's smart to run the car or truck or other vehicle A/C compressor from time to time every month or so even if you don't need its cooling capacity.

That operation helps keep the automotive air conditioner's drive shaft bearing lubricated and reduces the risk of refrigerant loss at that location.

How can I monitor the pressures in my home air conditioner system?

Where can I buy pressure sensors to put in my home air conditioning system?

I want to monitor the pressures and temperatures to see how it is running. High pressure line is 0.4 inches and the low line is 2.0 inches, copper. I prefer a section of pipe that can be brazed in place with a integral sensor that can be monitored. Not having much look with my searches.
The system is marked as R 410 refrigerant and a max pressure of 600 PSI. - by bkelly

Reply by (mod) - home A/C systems are not designed for continuous monitoring of refrigerant pressure: monitor temperature and air flow instead

BK

Thanks for an interesting question. I haven't seen the type of pressure monitoring equipment for residential air conditioning or heat pump systems that you describe either.

I think that is because of the great risk of a gauge blowout that loses all the refrigerant in a catastrophe.

In fact typically service techs usually just measure temperature on those refrigerant lines before they even bother hooking up a gauge set to the high and low pressure test ports right at the compressor condenser unit.

That's because they want to avoid extra trouble and also avoid the risk of introducing dirt or contamination at the valve connection.

And certainly no service tech will leave a gauge set permanently connected, for the ssme reasons

So what you might do is look for a couple of simple temperature sensors and to try monitoring that data.

What is the average low pressure on a 3.5 ton system in 90 degree ambient temp with R22

What is the average low pressure on a 3.5 ton system in 90 degree ambient temp with R22 - -

Reply by (mod) -

Start with a look at typical R22 pressures in the table found

at REFRIGERANT PRESSURE READINGS & CHARTS.

You also need to note the temperatures.

Charging Freon R410 did not fix my air conditioner

I have a split type FREON-R410 air conditioner . In cooling mode the pressure was 40 psi and after a few minutes it stopped working, so i thought that there was a lack in FREON. I charged the system with FREON-R410 but the pressure remained low and it was increased slightly to 55 psi and the unit stopped working again. Can you help me please ? - by Evangelos -

Reply by (mod) - Here are signs of low refrigerant or a bad TEV

Evangelo

Typically if refrigerant is somewhat low the compressor will keep running but temperatures will be too low and the cooling coil will ice up .

When refrigerant is very very low or all lost, the compressor will keep running but the cooling coil won't cool.

It's possible that your TEV (expansion valve) is not working - stuck or clogged. That would cause abnormally high pressure on the high side, low on the low side, and loss of cooling if refrigerant isn't making it through the valve into the cooling coil.

Followup by Evangelos

Thank you very much, you were so helpful to me

Reply by (mod) -

Glad to assist, Evangelos; let me know how the problem is finally solved.

Followup by Evangelos: Replacing the expansion valve fixed my air conditioner

I replaced the expansion valve with a new one and the air conditioner works fine. Thanks again. (Forgot to type my name on my previous Anonymous comment). - On 2018-09-12 by Evangelos

Reply by (mod) -

Great news.

Thank you so much for taking the time to follow up with the results. That will certainly help other readers.

How do I find out the factory charge of refrigerant on my heat pump?

What is the factory charge for an Aqua Comfort AC 125 vintage signature series heat pump? - On 2018-06-12 by Steve S

Reply by (mod) -

Almost all modern HVACR equipment provides the factory charge quantity on the data tag.

R22 low at 20 psi high at 200 psi - not cooling, what's wrong?

R22 system , no cooling whatsoever low side 20 psig high side 200 psig. What's going on? please. - by The repairman

Reply by repair tech -

@The repairman,

Sounds like the thermostatic expansion valve is not releasing refrigerant.

Maybe the liquid line was clogged or maybe the condenser coils of indoor inverter ac was clogged or maybe termostatic expansion valve is not working properly and need to be replace...

It might also be possible that the manifold gauge can break down over time especially the cheaper ones.

Why am I not seeing ANY reading on my low pressure refrigerant gauge?

Why is my low pressure gage not reading anything all of the sudden - by James Stennett

Reply by (mod) - if you see no reading at all on the low pressure gauge of your A/C refrigerant gauge set:

Defective gauge
Not properly connected
Compressor not running
are 3 possibilities

Truck air conditioner clutch won't engage and refrigerant is leaking out

Truck air conditioner has leak in radiator and I notice at this time the compress clutch is not engaging.

Is that normal. - by Luc

Reply (Mod)

No, Luc

Both of those items need repair.

 

To fix an old 3 ton heat pump in Arizona tech says we need a new capacitor and fan motor

I don't know if you can help me. I have a 10 year old 3 ton heat pump in Arizona. Last spring, before the hot weather came, we had the spring checkup done and the tech came off the roof and said we needed a new capacitor and fan motor to the tune of $900.

We told him to go ahead and a month later when it got time to run the AC, it would not work. The company sent out another tech and he said the capacitor was bad and exchanged it.

The unit then ran fine until we got the record heat of 118 a few days ago and the unit quit putting out cool air and the inside temps rose 5 degrees or more until evening when the unit started cooling.

We called the company again and the tech came and said we needed a new metering valve to the tune of $2500.

He took the bulb sensor off the suction line and said that would make the unit let max Freon through all the time and it would work until we decided to have the valve replaced or get a new unit.

After that, we got a second opinion and this tech said removing the bulb sensor would not make any difference and he put it back in place.

He said the compressor amps seemed low when it was running and with the high ambient temperature, it should be running about max amps.

The compressor was getting very hot and that is why it was shutting down. He said it indicates the compressor is wearing out and not operating efficiently anymore.

I know this may not be enough information for you to give me any advice but maybe you can possibly tell me which tech is on the right track. I think the first one was just trying to make a big sale because of the high price of replacing the metering valve. By the way, this is an R-22 unit.

Thanks, Smitty - On 2017-06-23 by Duane Smith -

What is the freon pressure in a freezer van?

What is the exactly pressure of freon in freezer van - by Ariel

Reply by (mod) - there is no single "exact" pressure number for automotive refrigerants

Sorry, Ariel but there is no single "exact" pressure number for refrigerants.

The refrigerant pressure you should see varies depending on what refrigerant gas is in use, where in the system you measure it, whether or not the compressor motor is running or has been off for a time, the specific refrigerant used, and the ambient temperature in and around the system.

That's why you see refrigerant pressure tables that express the pressure as a function of temperature.

See REFRIGERANT PRESSURE READINGS & CHARTS for example refrigerant pressures for different gases, and look at your van's A/C unit for a data tag (nameplate) or look in the owner's manual to see which refrigerant it's using.

Currently the most-common automotive refrigerant gas is R-134A (HFC-124a) but if your van is really old it may use "Freon" or R-12.

Which is the charging side for a central air conditioner?

I have a central air conditioning. Which is the low side or charging side ? by Anonymous

Reply by (mod) - which pipe is the low side?

Anon

The "Low side" of a typical refrigeration system in cooling mode will be the larger diameter pipe that enters the compressor motor. When the system is running, if it's working at all, that suction line will also be the cooler or colder line.

Question: is it possible to repair a leaky evaporator coil and then replace the refrigerant?

(Sept 30, 2014) p. choate said:
Repairman said there was a leak in evaporator. Can it be replaced and freon replaced.

Reply:

P. C.

IF the evaporator is corroded, patching it is a short term band-aid repair. More likely in that case it'd need replacement and then of course refrigerant replaced/recharged. Install a new filter drier too.

 

Question: short cycling A/C heat pump at 10 second interval

I have a 4yr old american standerd a/c heat pump unit.cycles every 10sec.

Tech serviced 12/06/2014 had to shut unit down01/20/2015. I live on a island only way to get here in winter is by plane. expensive! put gauge on high side,unit off temp out side 20degF read50#psi - Ed.

Reply:

Ed you are right to shut off the system; it may be that at low outside temp the unit wants to switch to backup heat anyway.

Short cycling could be a shot or frozen compressor, a burned out compressor base heater, a failed start/run capacitor, a failed relay or control board, a frozen expansion valve that's causing a high pressure safety switch to shut off the system, or something else.

With just your note I'm doubtful one could actually diagnose the system.

Is your backup heat running?

Start by checking the control relays and check for a clogged or frozen TEV

 

Question: why are the heat pump refrigerant pressures the same but I'm getting less heat out of the unit?

Why are my pressures the same when on heat pump mode cooling mode is fine but only getting 80 degrees of heat out of supply pressures running the same new unit txv at evap. Dan

Reply:

Perhaps because the ambient outdoor temperature is lower now. That can reduce the heat that the heat pump can extract from outdoor air.

 

Service tech charged me for 2.5 lbs of Freon but he didn't weigh it

I had a tech come to my home and hook up his gauges and I was told the system was low on freon r22. He said he added 2.5 lbs. I was not aware of any machine that was weighing the Freon,is there a way to calculate by reading gauges? Thank you.Someone told me I was being ripped off. - Claire.

Reply:

It is certainly possible to put a measured charge into HVAC equipment, and in fact that step can be required in many circumstances.

But with just pressure gauges and a gas cylinder, no, the amount was estimated, not measured. My service tech did the same thing. It's ... well you can fill in the blank ... a common practice.

 

Question: can I use a smaller diameter tubing on the suction or low side?

What difference would it make if I use 1/2 inch diameter refrigerant tubing on the low side instead of the recommended 3/8 in a short run? This is a pre-charged unit. -- Jim.

Reply:

I don't know, Jim but my guess is potentially none if the run is short enough that you don't have to adjust the refrigerant charge for the larger pipe diameter. Check the manufacturer's installation manual on charging instructions.

Though it's discussing the volume of water in a well, this article - inspectapedia.com/water/Well_Static_Head_Definition.php - will help you calculate the different volumes of two lengths of refrigerant tubing of different inside diameters.

 

Question: what is the exact psi on r22 and 134a?.

I have a Baldwin chiller,.what is the exact psi on R22 and R134a? - Joey.

Reply:

Joey, there is not an "exact" psi for a refrigerant.

There are normal operating pressure ranges that depend on the ambient temperature where the compressor is running as well as the properties of the compressor motor. The article above gives some typical pressures.

You can also look at a table, for each refrigerant type, to see what the refrigerant pressure would be at various temperatures and applications and compressors, starting from ambient.

 

Question: what is the stabilized pressure for split type ac?

Can I know the stabilized pressure for split type ac? I'm suspecting my unit over charge as it is not starting (compressor) it shows in the low side gauge 300 psi. ( Compressor is off.) thanks. - Ed.

Reply:

You won't see an overcharge changing the stabilized pressure in the HVACR system.

The stabilized pressure can be read from any of the refrigerant pressure/temperature charts linked-to

in REFRIGERANT PRESSURE READINGS & CHARTS

...

Continue reading at REFRIGERANT PRESSURE DIAGNOSIS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• PRESSURE CONTROLS & SAFETY SWITCHES
• REFRIGERANT GASES & PIPING - home
  • CAR / TRUCK AC PRESSURE SWITCH
  • FROST BUILD-UP on AIR CONDITIONER COILS
  • GAS DETECTION INSTRUMENTS
  • GAS EXPOSURE EFFECTS, TOXIC
  • GAS LAWS & CONSTANTS
  • GAUGE, REFRIGERATION PRESSURE TEST
  • REFRIGERANT CHARGING PROCEDURE
    • OVER CHARGED of REFRIGERANT, EFFECTS
    • UNDER CHARGED REFRIGERANT, EFFECTS
  • REFRIGERANT DRIERS & FILTERS
  • REFRIGERANT FLOODBACK, LIQUID SLUGGING
  • REFRIGERANT LEAK DETECTION
  • REFRIGERANT LEAK REPAIR
  • REFRIGERANT METERING DEVICES TEVs & EEVs
  • REFRIGERANT METERING CAPILLARY TUBES
  • REFRIGERANT OVERCHARGE EFFECTS
  • REFRIGERANT PIPING INSTALLATION
  • REFRIGERANT PRESSURE DIAGNOSTICS
  • REFRIGERANT CHARGE QUANTITY
  • REFRIGERANT QUANTITY on DATA TAG
  • REFRIGERANT HIGH HEAD PRESSURE DIAGNOSIS
  • REFRIGERANT LOW HEAD PRESSURE DIAGNOSIS
  • REFRIGERANT PRESSURE READINGS & CHARTS
  • REFRIGERANT PROBLEM TYPES
  • REFRIGERANT UNDERCHARGE EFFECTS
  • REFRIGERANT SIGHT GLASS
• AIR CONDITIONING & HEAT PUMP SYSTEMS - home
• SPLIT SYSTEM AC / HEAT PUMP REPAIRS

Suggested citation for this web page

REFRIGERANT PRESSURE READING & CHART FAQs-2 at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to AIR CONDITIONING & HEAT PUMPS

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