High suction pressure and low head pressure

To diagnose a bad TXV, look for: Low evaporator pressure. High evaporator and compressor superheats. Low compressor amp draw. Short cycling on the low-pressure control. Higher than normal discharge temperatures. Low condensing pressure. Low condenser split. Normal to high condenser subcooling.

High suction pressure and low head pressure. The high side guage was connected to the liquid line. Static, both guages are 160 psig. When the unit ran, BOTH guages dropped to about 130. The high side was perhaps 2-5 higher. The amp draw at the compressor was 8.6 RLA out of a 22.1 suggest maximum on the equipment sticker.

Blog. Pressure Points: Understanding the Importance of Head Pressure in HVAC. December 20, 2023by J & J Services. Table of ContentsToggle. Causes of High …

The margin of pressure over vapor pressure, at the pump suction nozzle, is Net Positive Suction Head (NPSH). NPSH is the difference between suction pressure (stagnation) and vapor pressure. In equation form: NPSH = Ps ‑ Pvap. Where: NPSH = NPSH available from the system, at the pump inlet, with the pump running.Hi, sorry you're having trouble. Low suction and high head is usually due to a restriction in the liquid line. Basically, you're starving the evaporator. If the unit has an expansion valve on the inlet to the evaporator, it may be defective. Some are adjustable, most residential ones, not. I would look there first.Scroll Troubleshooting Solution Chart - Copeland A/C Specific. Deep Vacuum Conditions. Deep vacuum can cause arcing damage to the Fusite pins. Models built after September 1991 have an internal vacuum protection and stop pumping when the pressure exceeds approximate. 10:1. Scroll compressors should never be used to evacuate a system, …Liposuction is the removal of excess body fat by suction using special surgical equipment. A plastic surgeon typically does the surgery. Liposuction is the removal of excess body f...Pressure gauges provide readings of the condensing and suction pressures, allowing technicians to monitor and adjust the head pressure as needed. B. Measuring Head Pressure in Refrigeration Systems To measure head pressure in refrigeration systems, technicians connect pressure gauges to the service ports on the high and low sides of the system.The most common, and obvious, reason for a service call is a space temperature that is too warm. And, just as common, is suction pressure and/or head pressure being involved in the cause. Often, the refrigeration system will still run, but it’ll run inefficiently because the suction pressure is too high while the head pressure is ...An R-22 evaporator running at 40F saturation temperature will have a corresponding pressure of 68.5 psig. Should the suction pressure drop below 57 psig, the coil temperature will drop below 32F causing moisture in the air to freeze on it (see Figure 4) causing no end of trouble. A R-410A evaporator running below 100 psig will freeze-up …

The purpose of this work is to provide empirical design models for low-pressure, subsonic Venturi nozzles. Experimentally validated simulations were used to determine the effect of nozzle geometry and operating conditions on the suction ratio (ratio of suction mass flow rate to motive mass flow rate) of low-pressure, subsonic Venturi nozzles, over a wide …Typical low pressure or suction side pressure for R410A is about 120 psi, varying by ambient temperature, here assuming 75°F, may vary by equipment and metering controls. 3. Typical high side pressure for R410A is < 600 psi at an ambient outdoor temperature of 95 °F, may vary by equipment. 4.I arrive to find a loud compressor, 200 psi suction and 275 head. First thing that comes to mind is bad valves. A few minutes later the compressor cuts off on internal overload. I take a hose and cool it off. 10 min later, compressor kicks back on and pressures now seem normal (130/325) 13 subcool , 19 delta t.The net positive suction head (NPSH) of a pump refers to the difference between the suction pressure at the pump's inlet and the fluid's vapor pressure at the system …High head pressure is typically accompanied by a low suction pressure. This combination can be indicative of restricted refrigerant. Essentially, this means that air and vaporized water travel through your HVAC’s evaporator until they get to the top of the compressor, where it remains because it will not condense.The most common causes of pressure in the head and face include allergies, ear infections, the common cold, muscle tension, sinusitis, stress and tension headaches. Increased intra...Typical low pressure or suction side pressure for R410A is about 120 psi, varying by ambient temperature, here assuming 75°F, may vary by equipment and metering …A dirty evaporator in an air conditioning system will cause what symptoms? Low Suction and Low Head Pressure (discharge) Technician "A" says that a compressor should pull 24" Hg during a vacuum test with 100 psig discharge pressure. Technician "B" says that a compressor should pull 26" hg to 28" Hg when discharging to the atmosphere.

Thread: Low suction - High Head. Thread Tools. Show Printable Version; 02-09-2005, 12:35 AM #1. saillar. View Profile View Forum Posts View Forum Threads ... If you attempt to bring up the suction pressure by adding more refrigerant, you'll be stymied by high head pressure and a suction pressure that does not come up much (with a …Head pressure: 400 lbs. Condenser air in: 140º F. I guess Condenser air out: what; about 160º F. I am guessing? LSC is: 30º F. - so the system has plenty of refrigerant in it Suction Pressure: 105 lbs. Suction Line Temp: 65º F. SSH: 30º - so the evaporator does not have enough refrigerant in it. What am I missing? PHM-----The SC might be normal , but the normal head for a r410 system w/ a 68* ambient should be closer to 300psi and the normal suction press should be closer to 110psi w/70* IDB. Those p/t's sound more like r22. kdean1, buttwheat liked this post. As others have said it sounds like a TXV and maybe low on juice.Scale results in a low head pressure in the cooling mode and high suction pressure in the heating mode. False. A domestic hot water loop is loop is often used for heating domestic hot water from the hot discharge gas coming from the heat pump's refrigerant compressor. True.

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Watch on. Compression ratio is the ratio of head pressure to suction pressure in an HVAC/R unit. Generally, compression ratios approach 2.5:1 on high-efficiency, 16+ SEER A/C systems. The highest compression ratio in A/C compressors is typically 11:1. Refrigeration compression ratios tend to be quite a bit higher (up to 26:1).One of the leading causes of low suction pressure is refrigerant leakage. When refrigerant leaks occur, the system’s refrigerant charge decreases, resulting in reduced pressure levels. Leaks can occur at various points, including connections, joints, valves, or even within the coils themselves. 2. Dirty Evaporator or Condenser Coils.When it comes to building a deck, there are many options available. One of the most popular places to shop for decking boards is at Lowes. Lowes has a wide selection of decking boa...High suction pressure plus low head pressure can risk product quality and safety. By John Tomczyk. FIGURE 1: A normal valve plate with suction and discharge valves. ... High Evaporator (Suction) Pressure — Refrigerant vapor will be drawn from the suction line into the compressor’s cylinder during the downstroke of the compressor. …Low suction pressure causes. low suction pressure is developed in the refrigeration system. Some of the most probable causes are as below, The coil is covered with dust or frost. Restriction in the refrigerant line. Filters and strainers are dirty. Faulty fan motor. Low room temperature. Faulty compressor.180 suction line pressure 320 discharge 10 degree temp split. No temp difference across the filter drier. I cleaned coils and checked airflow just to eliminate the variables. I recovered the refrigerant, changed the filter drier, charged about 2lbs before starting the compressor and the low side shot right up to 170. System holds about 8 lbs total.

Posted: 7/6/2012 2:35:12 PM EDT. My HVAC contractor recently saw head pressure of 350-400, normal to low suction. He diagnosed it as a restriction in the condensor coil, replaced condensing unit. The "changeout team" that installed the condenser saw exactly the same situation on the new unit. They left and now waiting for a re-evaluation from ...Low suction pressure and high head pressure is a condition where there is a decreased refrigerant pressure in the AC system and at the same time a high output pressure in a compressor. This condition is mainly caused by a defective or malfunctioning TXV valve .Reduced system performance. Increased energy consumption. Impact of High Head Pressure. Excessively high head pressure can:If you don't mind getting your hands a little dirty, some petroleum jelly can increase the suction power of your plunger to help with particularly stubborn clogs. If you don't mind...If it is 50˚ outside, the suction saturation temperature would generally be between 25˚ and 30˚ on a functioning system. Remember that in heat mode, the colder it gets outside, the lower the suction pressure, and the hotter it gets inside, the higher the head pressure.20% vapor. Eric, contamination in a refrigerant circuit will likely show a symptom of a. High head pressure. When all else seems to function properly a system with a high suction pressure and a low head pressure suggest. The compressor has leaky valves, and/or worn piston rings. When both the suction pressure and head pressure are low how …I will be sharing a pressure chart that may help you troubleshoot low pressure symptoms, high pressure symptoms. As well as other potential problems you may run into when trying to get your r410a or r22 systems to normal operating pressures. ... Outside air temp 95. Running for an hour, suction 120, head pressure between 315-350. Fluctuates ...Subcooling is liquid pressure converted to saturated condensing temp - liquid line temp. A SC reading of 40 degrees would put your line temp at 97 degrees, which would be cooler than your outdoor ambient. The only way for that to happen would be from incorrect instrument readings or non-condensibles in your system.The normal operating pressure for R-404A in a freezer at a temperature of 70 degrees Fahrenheit and a suction temperature of 30 degrees Fahrenheit would be around 9.6 psi. The low pressure should be 18-20 psi while the high pressure should be around 200 psi. However, this can vary depending on the specific conditions of the freezer and …Very high suctuion and head pressure on heating mode. Hello, I have a Rheem (2015) heat pump 2ton 410A, on cooling mode the system runs great; suction and liquid pressure are ok 185/360, super heat 10 F, with 90F outdoor temperature, now the winter is coming and the system on heating mode the gages read high pressure on both sides, begin from ...The most common, and obvious, reason for a service call is a space temperature that is too warm. And, just as common, is suction pressure and/or head pressure being involved in the cause. Often, the refrigeration system will still run, but it’ll run inefficiently because the suction pressure is too high while the head pressure is ...

Low suction pressure in both mode. b. High head pressure in both mode. c. Low head pressure in the heat mode and high suction pressure in the cool mode. d. High head pressure in the heat mode and low suction pressure in the cool mode. D. If the reversing valve were to stick in the halfway position, which one of the following would the service ...

The SC might be normal , but the normal head for a r410 system w/ a 68* ambient should be closer to 300psi and the normal suction press should be closer to 110psi w/70* IDB. Those p/t's sound more like r22. kdean1, buttwheat liked this post. As others have said it sounds like a TXV and maybe low on juice.Lower suction pressures generally result in a higher DTD, and higher suction pressures usually result in a lower DTD. When we look at head pressure, we’re actually learning …Read also: R410a Pressure Chart High and Low Side. psi: Pound per square inch, unit of pressure. FAQ What is the normal suction pressure on a 404a walk in the freezer? The normal suction pressure on a 404 a walk in freezer is around 10-20 psig (10 is ideal) on the suction side if working properly. And the high side is about 180 or so.Number 2 is incorrect, metering device part depends on system to system. High load is correct. Look at your liquid line temps, subcooling and approach temps. They will help diagnose high head issues. There is another cause of high head pressure, mismatched (higher btu) compressor. Different refrigerant in the system.Suction pressure occurs on the low-pressure side of the system where refrigerant is drawn into the compressor. Head pressure, or high side pressure, should not be confused with these other readings as each serves a specific purpose in maintaining an effective HVAC cycle.An R-22 evaporator running at 40F saturation temperature will have a corresponding pressure of 68.5 psig. Should the suction pressure drop below 57 psig, the coil temperature will drop below 32F causing moisture in the air to freeze on it (see Figure 4) causing no end of trouble. A R-410A evaporator running below 100 psig will freeze-up …Typical low pressure or suction side pressure for R410A is about 120 psi, varying by ambient temperature, here assuming 75°F, may vary by equipment and metering controls. 3. Typical high side pressure for R410A is < 600 psi at an ambient outdoor temperature of 95 °F, may vary by equipment. 4.Net Positive Suction Head or NPSH for pumps can be defined as the difference between the suction pressure and the saturation pressure of the fluid, expressed in terms of height of liquid column. …Note that variations in the atmospheric pressure can and will affect the NPSHa value. Now you just need to convert the atmospheric pressure from psia to feet of head. Multiply 14.7 by 2.31, and the result is 33.957 feet, rounding to 34 feet. The value for the first component in the equation is 34 feet.Suction Head. Based on the Energy Equation - the suction head in the fluid close to the impeller *) can be expressed as the sum of the static and velocity head: h s = p s / γ liquid + v s 2 / 2 g (1) where. h s = suction head close to the impeller (m, in) p s = static pressure in the fluid close to the impeller (Pa (N/m 2), psi (lb/in 2))

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This small amount of heat to reject will cause a low condensing pressure and temperature. Most of the refrigerant will then be stored in the condenser and receiver, simulating a pumped-down refrigeration system. Symptoms of a liquid line restriction include: Low evaporator (suction) pressure; High superheats;Fig. 3.55 illustrates this by plotting the pump discharge head vs. flow for high- and low-suction tank conditions. The control valve, however, tries to maintain a steady pressure. As a result, the flow rate varies as the suction pressure varies. In some cases, the flow rate may drop to below the recommended minimum at very low head conditions. A bad check valve on an air conditioner, heat pump or similar HVACR equipment can show up as abnormally low or abnormally high suction line pressures, or as abnormally low or high superheat. Experts suggest using an IR heat gun or similar tempeature measuring tool to check the tempeature of the refrigerant line on each side of the valve. The Net Positive Suction Head (NPSH) margin is a crucial factor that is commonly overlooked while selecting a pump. ... Pumps work by creating a pressure differential between the inlet and the outlet—the high pressure at the inlet causes fluid to flow towards the low pressure at the outlet. As the fluid flows through the pump, it …Because the pump's suction pressure, PIP, is known, the pressure increase to be exerted by the pump, Δ ppump = pd − PIP, is easily found. This value, however, if converted to head, gives exactly the pump's required head, i.e., the TDH value as found from the following formula: (5.38) where. TDH = total dynamic head, ft.In the cooling mode this will result in low suction pressure and low discharge pressure. Sub cooling would be extra high. However, heatpumps can't always be charged accurately using sub cooling alone. Usually "a stuck check valve" can be freed-up by using a strong magnet.This means the pump takes suction pressure, adds more pressure (the design pressure), and generates discharge pressure. So, the discharge pressure is equal to the suction pressure plus the pump’s design pressure. The discharge pressure of the pump should be approximately equivalent to the total dynamic head (TDH) required by …The normal operating pressure for R-404A in a freezer at a temperature of 70 degrees Fahrenheit and a suction temperature of 30 degrees Fahrenheit would be around 9.6 psi. The low pressure should be 18-20 psi while the high pressure should be around 200 psi. However, this can vary depending on the specific conditions of the freezer and the ...we note (and you probably know better than I) that making sense of any refrigerant pressure reading requires also a note of the ambient temperature. If we take 75°F as an example point, R410 low side typical pressure would be about 120 psi and the high side between 410-420 psi. Your high side is a little low.We would like to show you a description here but the site won’t allow us.Hi, I just put a new compressor on a gas pack. I charged it to the correct amount of refrigerant o the name tag. My ambient temp. is 100 degrees and the unit running with a high high side pressure a high suction pressure and high superheat and sub cooling. The indoor temp is 87 degrees. i was told that the high indoor temp is why my …Typical low pressure or suction side pressure for R410A is about 120 psi, varying by ambient temperature, here assuming 75°F, may vary by equipment and metering … ….

An over-charged system will cause efficiency problems and can cause component damage, but the most obvious sign of an over-charge in heating mode, is that it will trip on high head pressure. Jeff Rosenblum. Technical Support. 16 Years Industry Experience. Cell (330) 962-2491.20% vapor. Eric, contamination in a refrigerant circuit will likely show a symptom of a. High head pressure. When all else seems to function properly a system with a high suction pressure and a low head pressure suggest. The compressor has leaky valves, and/or worn piston rings. When both the suction pressure and head pressure are low how …Step 1. Scale in a geothermal heat pump's fluid system results in an overall increase in fluid temperature high head pressure in the cooling mode and low suction pressure in the heating mode an overall decrease in fluid temperature low head pressure in the cooling mode and high suction pressure in the heating mode.Midodrine is also called Bramox. It is used to treat low blood pressure known as postural hypotension. Try our Symptom Checker Got any other symptoms? Try our Symptom Checker Got a...The SC might be normal , but the normal head for a r410 system w/ a 68* ambient should be closer to 300psi and the normal suction press should be closer to 110psi w/70* IDB. Those p/t's sound more like r22. kdean1, buttwheat liked this post. As others have said it sounds like a TXV and maybe low on juice.Suction Head. Based on the Energy Equation - the suction head in the fluid close to the impeller *) can be expressed as the sum of the static and velocity head: h s = p s / γ liquid + v s 2 / 2 g (1) where. h s = suction head close to the impeller (m, in) p s = static pressure in the fluid close to the impeller (Pa (N/m 2), psi (lb/in 2))Low suction pressure causes. low suction pressure is developed in the refrigeration system. Some of the most probable causes are as below, The coil is covered with dust or frost. Restriction in the refrigerant line. Filters and strainers are dirty. Faulty fan motor. Low room temperature. Faulty compressor.Low suction pressure in both mode. b. High head pressure in both mode. c. Low head pressure in the heat mode and high suction pressure in the cool mode. d. High head pressure in the heat mode and low suction pressure in the cool mode. D. If the reversing valve were to stick in the halfway position, which one of the following would the service ... High suction pressure and low head pressure, Flashcards Study Guide 29 | Quizlet. In a 2-ton capillary tube system, the unit does not develop full capacity. Heat pressure is low and suction pressure is high. What is the problem? Click the card to flip. BLANK. Quizlet has study tools to help you learn anything. Improve your grades and reach your goals with flashcards, practice tests and ..., When both the suction pressure and head pressure are low, how might a technician determine that the problem is low evaporator airflow and not a low refrigerant charge ... When all else seems to function properly, a system with a high suction pressure and a low head pressure suggests _____. the compressor has leaky valves and/or worn piston ..., what causes a high suction pressure and a normal head presssure on an r22 system besides low air across the evaporator coil? Can air in the system cause this situation? TD is 17f. otd is 91degrees liquid line pressure is 230psi; suction pressure is 90psi. ... High side is 151 low 48-50psig., The suction pressure, on the other hand, is the pressure at the evaporator, where the refrigerant absorbs heat and evaporates. ... Higher loads may result in higher head pressure, while lower loads may lead to lower head pressure. Refrigerant charge: The amount of refrigerant in the system plays a significant role in head pressure control. …, In the cooling mode this will result in low suction pressure and low discharge pressure. Sub cooling would be extra high. However, heatpumps can't always be charged accurately using sub cooling alone. Usually "a stuck check valve" can be freed-up by using a strong magnet., Low pulse pressure, or low blood pressure, is not always indicative of a health problem and it is usually not alarming to doctors unless the patient is exhibiting other symptoms ca..., 1. Reduced Cooling Capacity. 2. Reduced Airflow From the Vents. 3. Increased Energy Consumption. 4. Poor Indoor Air Quality. How to Diagnose and Fix Low Suction Pressure High Head Pressure. Step 1: Inspect the System for Leaks. Step 2: Measure the Pressure and Temperature. Step 3: Replace or Repaire Components. Add Proper Refrigerant., Midodrine is also called Bramox. It is used to treat low blood pressure known as postural hypotension. Try our Symptom Checker Got any other symptoms? Try our Symptom Checker Got a..., This low head pressure and higher-than-normal evaporator pressures will decrease the compression ratio of the compressor, causing high volumetric efficiencies. This will increase the pumping rate of the compressor, and a balance may be reached if the compressor can keep up with the high refrigerant flow in the evaporator., This article series explains the causes of high head pressure at an air conditioner or heat pump compressor motor? This article lists twelve causes of high …, Greetings, I am working on a R22 Lennox Split Heat Pump 3 ½ ton. The unit will trip on the compressor relief valve in heating. I was unable to test the unit S/C and S/H accurately, due to the High Side pressure building up so fast with in a minuet will be hitting 400psi and blow the low side would sit at about 50psi. I tested the RVR from cooling to …, Try our Net positive suction head calculator or: In your reservoir, get fluid surface pressure: P surface. Get the distance between the pump and liquid surface: Z. If the tank is above the pump, multiply this value by -1. Obtain the vapor pressure for the system's temperature: P vapor. Also, its density is ρ. Note that g represents gravity., The margin of pressure over vapor pressure, at the pump suction nozzle, is Net Positive Suction Head (NPSH). NPSH is the difference between suction pressure (stagnation) and vapor pressure. In equation form: NPSH = Ps ‑ Pvap. Where: NPSH = NPSH available from the system, at the pump inlet, with the pump running., Subcooling is liquid pressure converted to saturated condensing temp - liquid line temp. A SC reading of 40 degrees would put your line temp at 97 degrees, which would be cooler than your outdoor ambient. The only way for that to happen would be from incorrect instrument readings or non-condensibles in your system., What is NPSH-R? NPSH-R is a pump property. Net Positive Suction Head Required is quoted by pump manufacturers as a result of extensive testing under controlled …, lower suction pressure and high discharge pressure. Study with Quizlet and memorize flashcards containing terms like which of the following is NOT a symptom of a hermetic system that is low on refrigerant?, frost on the suction line indicates;, an increase in head pressure causes _____ refrigerant to flow through a capillary tube. and more., A cold suction line (low superheat) with low suction pressure is a symptom of low evaporator air. A liquid restriction would result high superheat (warm suction line). The high head probably due to the other guys overcharging, trying to get the suction pressure up. But the low air problem would result in high head pressure in the heat cycle., Yahoo announced today that it was repurchasing 40 million of its shares from activist investor Third Point, bringing the hedge fund’s Yahoo stake to below 2%. That means that Third..., Positive Suction Head (NPSH)—the pressure provided at the suction of the pump less the fluid’s vapor pressure — is too low. When fluid pressure on the trailing side of the impeller blade (opposite the pump intake) falls below the vaporization point of the fluid, vapor bubbles begin to form., High Discharge Pressure on heat pump. I was working on a customers heat pump today, A lennox HPXA19-060-230-02 with A cbx32mv-060-230-6-02. It kept short cycling but was giving off 100 f supply. I put my guages on at heat mode and it would trip discharge line temp at 650 PSI (154.7 F) on discharge with a 200 f discharge line temp., Karcher pressure washers are renowned for their powerful cleaning abilities and durability. However, like any mechanical device, they can encounter issues over time. One of the mos..., High Discharge Pressure on heat pump. I was working on a customers heat pump today, A lennox HPXA19-060-230-02 with A cbx32mv-060-230-6-02. It kept short cycling but was giving off 100 f supply. I put my guages on at heat mode and it would trip discharge line temp at 650 PSI (154.7 F) on discharge with a 200 f discharge line temp., 20% vapor. Eric, contamination in a refrigerant circuit will likely show a symptom of a. High head pressure. When all else seems to function properly a system with a high suction pressure and a low head pressure suggest. The compressor has leaky valves, and/or worn piston rings. When both the suction pressure and head pressure are low how …, , If you don't mind getting your hands a little dirty, some petroleum jelly can increase the suction power of your plunger to help with particularly stubborn clogs. If you don't mind..., It's tempting to head to the Caribbean this winter but here's why you might want to avoid the trip -- even to islands with low COVID-19 infection rates. Editor’s note: This post ha..., r410a high/low pressures; Cookie Consent ... If it weren't for the high head pressure and the high SH and SC I'd leave it alone. THX Jim Reply . 06-07-2021, 04:45 PM #2. pecmsg. View Profile View Forum Posts View Forum Threads ... Suction Pressure: 105 lbs. Suction Line Temp: 65º F. SSH: 30º - so the evaporator does not have enough ..., what causes a high suction pressure and a normal head presssure on an r22 system besides low air across the evaporator coil? Can air in the system cause this situation? TD is 17f. otd is 91degrees liquid line pressure is 230psi; suction pressure is 90psi., Peal. 3 posts · Joined 2009. #46 · Jul 12, 2009 (Edited) I think bwalley is correct. 3 things will cause high head pressure; poor air flow across condenser, overcharge, or non condensable in system. Recover charge, check system for leaks, pull vacuum, and weigh in new charge., Take the suction pressure and use the pressure/temperature chart to convert it to temperature. Let’s say the suction pressure is 60(Psi) which converts to 34F. And assuming that the suction line temperature is 44F. Then to get superheat we just get the difference between the two temperature readings. In this case, we have 10F of superheat., This will cause the following symptoms: Low evaporator (suction) pressure; High evaporator and compressor superheats; Low compressor amp draw; Short …, Try our Net positive suction head calculator or: In your reservoir, get fluid surface pressure: P surface. Get the distance between the pump and liquid surface: Z. If the tank is above the pump, multiply this value by -1. Obtain the vapor pressure for the system's temperature: P vapor. Also, its density is ρ. Note that g represents gravity., In the cooling mode this will result in low suction pressure and low discharge pressure. Sub cooling would be extra high. However, heatpumps can't always be charged accurately using sub cooling alone. Usually "a stuck check valve" can be freed-up by using a strong magnet.