- An essential troubleshooting list of things that cause high head pressure
- What is high head pressure?
- Condenser Fan Motors
- Condensing Units and Condenser Coils
- The Line set and crucial devices in the line set
- Non-condensing gases in the system
- Refrigerant overcharge
- Design conditions and head pressure
High Head pressure for a refrigeration system, including a heat pump or air conditioner can cost you more money and possibly lead to premature failure of the compressor. It can also cause a malfunction in the system that will lead to reduced capacity for cooling and heat (for a heat pump) or the system not functioning at all.
For any refrigeration system, it is vital that all pressures, the suction, and the head pressures are normal and as designed for the load and outdoor ambient temperature.
Some of the initial and essential things to look at when troubleshooting high head pressure include the condenser fan motor working and operating at the proper RPM’s and clean condenser coils. More advanced things to look at include refrigerant overcharge and a restriction in the refrigerant lines. There some other things you can look at when a heat pump or air conditioner is experiencing high head pressure.
High Head Pressure Air Conditioner Heat Pump
Condenser Fan Motor | What Causes High Head Pressure?
Top Reasons for High Head Pressure
- Bad Condenser Fan Motor
- Dirty Condenser Coils
- Refrigeration device crimp or plugged
- Refrigerant overcharge
- Non-condensing gases in the system
- Extreme operation above design specifications
When first encountering the problem of high head pressure, it is essential to check the basics first. The condenser fan motor and the condenser coils are the most common problems I have found with the issue of high head pressure.
Of course, other issues can cause high head pressure but these are the most common. In one case, the condenser fan motor appeared to be working fine but through the process of troubleshooting, I did an RPM check of the condenser fan motor and found it to be turning at 900 RPMs. The test resulted in 200 RPM’s lower than what it was supposed to be turning.
I know all technicians do not carry an RPM gauge tester, but I have found it very useful in a lot of cases where the problem seemed to be mysterious. Use an RPM meter solved some of those mysteries, especially with fan motors and pumps that are required to turn at a specific RPM. The RPM meter I carried required reflective tape to be applied as close to the motor shaft as possible. There are other types of RPM meters, but the one with reflective tape is the one I have and always given me the best results.
Condenser Coils | High Head Pressure Air Conditioner Heat Pump
Plugged up condenser coils is another big problem commonly encountered with high head pressure. That is also probably the easiest one to solve, provided you have a water hose nearby. A little coil cleaner and spraying water (from the inside out) will solve that problem and drop the head pressure to normal levels. I usually advise the homeowners to turn off their air conditioner or heat pump when they are cutting the grass.
By following that advice, it keeps a lot of grass out of the air conditioner or heat pump condenser coils. Therefore, they do not have that problem of grass plugging up the coils. Make sure the condensing unit stays as clean as possible, and you can avoid this problem. This is the most common problem I have found that causes compressors to trip on high head pressure.
Other problems that can result in high head pressure from condenser coils are corroded coils. That can happen as a result of living near the coast (environmental issues with the air) or animal urine. I had a call from a residential customer with this problem. It seems their dog thought the condenser was a fire hydrant and continuously did his business on the condenser.
The condenser lost, and the corroded coils caused the high head pressure. Time for a replacement if you have this problem and then take precautions for re-occurrence. Manufacturers typically have a salt spray rating on their condensers. Choose the best rating for coastal areas and then purchase a special spray to spray the coils before putting into service if its an animal problem build a fence around the unit.
Restriction in the Line Set | High Head Pressure Air Conditioner Heat Pump
Can a TXV or Metering Device Cause High Head Pressure?
If you have a high hear pressure in a condenser and the fan motor is working fine, and the coils are clean, then you need to go hunting. Check all your filter driers. Some filter driers have pressure access ports on them so you can see if the filter is plugged using your gauges.
Other filter driers without the pressure access ports need to be checked by temperature. Using an infrared temperature gun is not always the best method in this case as infrared’s do not work very well on copper. I use a digital thermometer that has individual probes.
The readout will give me the differential temperature. Usually, a few degrees is okay. Still, when you get a more significant number for a differential temperature from one side of the filter-drier to the other, then you have a restriction, and you need to replace the filter drier.
Other restrictions can be the metering device getting plugged up with debris. I have found both the piston type and the TXV type with restrictions that caused high head pressure. In one case, I found a bead of solder was restricting the piston. That was from improper soldering methods, namely using too much solder. Another example was a TXV. Once I found the TXV, it was frosted.
Replaced the TXV and the system returned to normal operation. Crimped copper lines can also cause restrictions. The satellite TV installer crushed the liquid line in an attic in one case, and the other case was unknown how it happened, but it was crimped and causing high head pressure.
Non-Condensing Gases in the Refrigeration System | High Head Pressure Air Conditioner Heat Pump
In this particular case, the homeowner installed the system themselves. It was one of those purchased online deals. They bought the unit online and decided to install it themselves to save money. The customer did a decent job with most of it except when it came to the refrigeration part. They were clueless.
They must have read the instructions to a certain point and then ignored the rest of it. No vacuum was pulled. They soldered it up, hooked up the wiring, and put the charge to it. The pressures were fluctuating wildly. At first, they were pretty good at playing dumb, but then the wife fessed up and told me what they did.
I recovered everything out of the system, did a proper triple evacuation, and recharged. Everything went back to normal. In most cases, I give the homeowner a warranty on my work. In this case, I did not. I never heard from them again, so I am guessing it went well for them.
How can you tell there are non-condensing gases in the system? The pressures will fluctuate wildly, giving you a definite high head pressure reading. That is, at least, from my experience. Has the system been accessed recently by someone? Is it a new installation? Hopefully, the homeowner will fess up like mine did when I found the non-condensing gases problem, and you will be able to solve the problem much quicker.
Refrigerant Overcharge | High Head Pressure Air Conditioner Heat Pump
That happens quite frequently, even with HVAC technicians. They do not use proper procedures when charging the system. Using a chart, collecting basic data such as indoor wet bulb, outdoor dry bulb, and using the pressures to charge the unit properly is a necessity. Otherwise, you are just guessing. Using the proper superheat or subcooling methods to charge a unit are absolutely essential at getting it right the first time.
I’ve heard customers say, “I think I need some more Freon to make it colder.” They don’t understand that adding more Freon in properly charge system will make it not colder. The system will use more power and not as cool as effectively. Hit that sweet spot on your superheat or subcooling chart, and everyone will be happy, and you can avoid high head pressure in the system.
Conclusion | High Head Pressure Air Conditioner Heat Pump
Don’t forget the design conditions when thinking about high head pressure. Most HVAC systems are designed for a maximum outdoor ambient temperature of 95° F. So, if the temperature is at or above 95° with high humidity, then you will likely also experience high head pressures.
Or at least above normal head pressure for the air conditioner or heat pump. The system is working hard to remove not only the sensible heat load but also the latent heat load so the pressures will be high in those conditions.
Lastly, if you re ever in a situation that is a big mystery and hard to figure out, step back and take a deep breath when you return to check the basics with a fresh new look. Good luck. Comments are welcome below.
High Head Pressure Air Conditioner Heat Pump
Technical Resource: Refrigeration and Air Conditioning Technology
I have a question. I have a large LG window unit. Around 26,000 BTU. I bought it 2021. It keeps coding that it has high head pressure. This is the beginning of the second summer that I’ve used it. I only used it for a couple months last year. It seems like it’s not blowing through the rear condenser. Only a small amount of air blows out the back. The condenser is very clean. Scrubbing Bubbles and water hose with a sprayer. The fan is turning very fast. Unit gets very cold what time it will run. And it kicks off and gives me a CH 34 code. Is the exhaust fan just a bad design? The blades not designed correctly to push air? I would appreciate any buddies advice on this. I am on disability and cannot afford to buy another one.
It should still be under warranty. Call LG for service. Could be a bad sensor.
why doesn’t the compressor come back on after going off on high head pressure. I can push in the contactor and it will run as long as I hold the contactor in. The condenser fan is continuously running.
Because the control circuit runs through the safety switches before it completes the circuit to the compressor contactor.
I’m having an odd problem where I’m getting a high pressure lockout code at the roughly the same time each morning. The past three mornings I’ve woke up to my outside unit off with the error code indicating high pressure lockout. All three times have been around 4 am. I’ve cleaned the coils, checked the fan motor, visually inspected the coolant line for crimps and all seems fine. After I reset the units board the system starts up and runs for the day. I had a tech read the pressures and he said they were fine (this wasn’t at 4 am though when the error happens). Any ideas what could cause this?
Off the top guess a bad switch or something screwy with defrost board.
I attended a two day a week course 96 credit hrs at Albemarle College. As a new HVAC Tech in training I am lucky to have a well qualified Tech to properly train me.
Skyler has gone over these very scenarios! There is so much to learn. But I have to keep studying. This was very helpful in my continued training.
Never stop learning. Technology is always evolving. Good luck in your career.
I thought I am a technician
But after 10 years I noticed that there’s a lot of things I should have to know.
To be a good technician is not pap and meat
It takes all of life,
I want to say thank you very much for this page.
Clean two-year old Carrier 3-ton system. System short cycling – possibly due to high-side cutoff. Ambient outside about 80 degrees. Technician saw pressure fluctuations of 450-580 or so high side and a 10 psi range on low side centered around 132 or so. Oddly, they shot to their highs together, bled down to the lows over about 40 seconds, shot back up, ad infinitum. I would have expected them to be opposite. He guessed and bled some charge. High side range simply shifted to 350-480 or so.
He is scratching head and saying he hasn’t seen this in decades of experience. Wants to just start replacing starting with the lines because they are cheapest. I’m not thinking restriction or TXV because the high and low sides were going up together and down together. I’d think a TXV closing would cause high side to go up and low side to fall.
Non-condensables? Why do the sides go up and down together instead of opposite?
I’ve seen TXV’S ice up if they are restricted or not functioning. Follow the lines and components and see if there is a distinguishable temperature difference from one part to another. I would bet its a restriction somewhere and likely the TXV. Can’t really say for sure but I’ve seen those symptoms before and the last time it was a TXV.
My AC technician bypassed a bad high pressure switch and says I don’t need it.
I live in Central Florida and we experience some very hot and humid days in the summer.
After reading your article, I disagree with the technician. My unit is 11 months old and I don’t want to have more serious problems down the raid.
Shouldn’t I insist the HP switch be replaced?
Never bypass a safety switch……………never ever ever ever!!! Yes, it needs to be replaced.