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.

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.

On 2019-05-14 by (mod) - low pressure switch won't let the A/C start

You may need to repair or replace a refrigerant metering device like a thermostatic expansion valve or capillary tube. You should not force the system to run because you're a subverting a safety device. Forcing it to run could be dangerous.

On 2019-05-14 by Nessisso

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

On 2019-04-29 13:44:49.297481 by (mod) -

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

On 2019-04-29 04:20:05.347766 by Henry

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 2018-11-15 19:08:39.126002 by (mod) -

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.

On 2018-11-15 04:31:55.659869 by bkelly

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.

 

On 2018-11-15 by (mod) - buy pressure sensors to put in my home air conditioning system

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.

On 2018-11-15 by bkelly

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.

On 2018-10-02 05:47:03.307980 by Anonymous

What is the average low pressure on a 3.5 ton system in 90 degree ambient temp with r22

On 2018-09-24 22:51:01.933864 by (mod) -

I'd start with a look at typical R22 pressures in the table above in this article. You also need to note the temperatures.

Could be a bad TEV.

On 2018-09-20 03:37:51.902237 by Eric

Hello to whom can help me 70 psi low side and a 310 psi high side
Green r 22 readings are 40 psi low side and around 140 high side what is the problem?

On 2018-09-13 02:13:53.487750 by (mod) -

Great news.

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

On 2018-09-12 19:48:53.412923 by Evangelos

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 12:25:52.589736 by Anonymous

I replaced the expansion valve with a new one and the air conditioner works fine. Thanks again.

On 2018-09-08 22:57:02.331234 by (mod) -

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

On 2018-09-08 20:39:59.040582 by Evangelos

Thank you very much, you were so helpful to me.

On 2018-09-08 17:18:29.779110 by (mod) -

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.

On 2018-09-08 16:35:10.874564 by Evangelos

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 ?

On 2018-06-12 17:07:19.400671 by (mod) -

Most hvacr equipment provides the factory charge quantity on the data tag.

On 2018-06-12 13:41:47.862678 by Steve S

What is the factory charge for an Aqua Comfort AC 125 vintage signature series heat pump?

On 2018-08-28 18:54:29.778951 by (mod) -

Thanks anon

On 2018-08-28 15:54:11.677032 by Anonymous

@The repairman,
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...

On 2018-07-09 02:39:53.986058 by (mod) -

sounds like the thermostatic expansion valve is not releasing refrigerant

On 2018-07-08 17:46:26.376043 by The repairman

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

On 2018-06-24 01:53:12.036207 by (mod) -

That seems a bit short to me.

In particular though if the system is shutting off before reaching the set temperature on the thermostat that's certainly a reason to call for repair.

On 2018-06-24 00:37:18.683596 by Jim

Short cycling. Return air 74, supply 62 degrees. Thermostat set at 78, room air temp on thermostat says 78 also. System will come on and run for about 6 minutes and shuts down. Comes back on about 10 minutes later. Is that considered "short cycling"?

On 2018-05-18 15:45:50.078773 by Michael

High side high presure lowside high presure

On 2018-04-30 21:08:29.814491 by (mod) -

What your note tells us, particularly repeatedly adding R22 refrigerant to a system is

1. the system has a leak

2. we are contaminating the envioronment and adding to the problem of global warming

3. we are using an obsolete refrigerant that has been phased out for good reason

4. It would be best to either find someone who will find and fix the leak or abandon the equipment.

The milkman's job and delivery route have become obsolete. So should we treat the HVAC refrigerant delivery truck.

On 2018-04-30 20:57:58.507052 by Rick Harrison

I've had to add R22 to my comfortmaker central unit for the last,3 years..still does a decent job... I just hooked up my gages and the low side is reading around 70 psi but the high side is reading zero...what's that telling us..thanks

On 2018-04-22 10:02:40.958871 by Mani

How much pressure on air conditioning

On 2018-04-21 06:14:02.138257 by daewoo bus

how psi low side

On 2018-04-15 22:35:19.939753 by (mod) -

Defective gauge
Not properly connected
Compressor not running
are 3 possibilities

On 2018-04-15 21:27:23.900576 by James Stennett

Why is my low pressure gage not reading anything all of the sudden

 

On 2017-11-09 by Gdlkumar

Sir good in information. sir I have simple problems please rectify to answer my

Reply (Mod)

No, Luc

Both of those items need repair.

On 2017-06-26 by Luc

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

On 2017-06-23 by Duane Smith - old 3 ton heat pump in Arizona.

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 2017-06-15 by Carol - Goodman AC unit diagnosis

I have a Goodman a/c unit ,it's a big one.not sure if it is suppose to sound real loud.my landlord will not hire someone to check it out.he tells me it's suppose to sound that way because it's brand new.oh..he installed it himself.wondering if the p.s.i. is to high for the unit.

On 2017-02-11 by (mod) - there is no single "exact" pressure number for refrigerants

Sorry, Ariel but there is no single "exact" pressure number for refrigerants. The pressure varies depending on 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.

On 2017-02-11 by Ariel

what is the exactly pressure of freon in freezer van

On 2016-09-09 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.

On 2016-09-09 by Anonymous

I have a cintrel air conditioning witch is the low side or charging side

On 2016-09-01 by Anonymous Amana 3nad 1/2tona/c

I have an Amana 3nad 1/2tona/c unti and I know it needs to have freon recharged. What are the reading I should try to attain upon recharging the unit with Freon.

On 2016-08-31 by luhar jigar

My ID is.... malvito4@gmail , thank you

Hy, I am doing project on A/C system so for that purpose I need to know the inlet and outlet pressure and temperature of compressor and condenser for 1 tonne refrigerant. So can you please suggest me any link/website or any idea regarding this? So that I can easily get to solve my problem....thank you!!

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

(Jan 30, 2015) ed said:
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.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 20deg f read50#psi

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:

(Nov 14, 2015) Dan said:
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.

Reply:

Perhaps because the ambient outdoor temperature is lower now.

Question:

(June 10, 2015) Shembesh said:
If the evaporator pressure is maintained at 400Ka while the condenser pressure is varied according to the outdoor condition, at various outdoor temperatures ranging from 25 to 45 c

how do i know the pressure of the condenser
if the temperature difference of 10c between the condenser and the ambient ?

(Aug 20, 2015) Clair said:

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.

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:

(Mar 11, 2016) jim said:
What difference would using 1/2 inch in the low side instead of the recommended 3/8 in a short run, this is a pre charged unit.

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?.

(Apr 21, 2016) Joey said:
I have a baldwin chiller,.what is the exact psi on r22 and 134a?.

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: stabilized pressure for split type ac?

(May 23, 2016) ed said:

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 off) thanks.

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

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

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

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