Summary: High head push faults can happen on wait conditioners because that a variety of reasons. This article will comment on two scenarios wherein high head push faults emerged because of two distinct and also common problems.

The first problem emerged when Liebert computer system room air conditioner condenser fins were blocked by cottonwood seeds. The second example was brought about by a faulty condenser fan that would not revolve on.

You will check out that both instances left distinctive signatures or trends that gimpppa.org’s beat charts were able come show. Ns will evaluation the basics the the refrigeration cycle i m sorry can aid you understand why these two difficulties caused a high head pressure fault.

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Key concepts:

High head pressure faults leave distinctive signatures.Short cycling can be one indicator that a high head pressure fault.The refrigeration cycle can assist you understand the probable causes.

Even though HVAC units often live on peak of roofs, the doesn’t typical they space immune come the environment about them. The very first example of a high head push fault developed at a customer’s data center and office building in ft Worth, Texas. It to be the middle of June and spring was winding down and also one that the sexy summers on document in Texas was start to bear under on the state. Below you have the right to see the temperature graph for the day i beg your pardon topped out at 105 levels just ~ 4 pm.


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Temperature graph for fort Worth on June 18, 2011


These Liebert units deserve to show brief cycling wherein they will rotate on for simply minutes and also then turn off again because that minutes. Follow to sources we’ve speak to they space designed to take care of this since many client of computer room waiting conditioners want to have actually fairly continuous temperatures.

You can see native the graph listed below that just after 11:00 am the lines get even closer together and also denser indicating the the unit is to ride bicycle on and also off even more frequently. This to be not normal behavior and was the very first indication the there to be a problem developing.

At 3:21 pm the unit shut under completely. Over there were 2 Liebert units offering cool air come a data facility room housing about $1.5 million in equipment. On warm days, both units are required to cool the load produced there. A gimpppa.org alarm was sent out to the customer who was able to obtain the unit back up and also running before they had actually to take any type of drastic actions to minimize the fill in the center by turning off machines. This additionally averted the associated lack of company to your customers not to mention all the extra time it takes your IT staff to shutdown and restart a huge server system.


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High head press fault on computer system room air conditioner


What happened to reason this problem? The Liebert manage panel in the data center indicated a high head push fault had occurred, yet no alert from that mechanism was sent. After ours alert to the customer, your authorized Liebert representative was called out and determined the the condenser coils had been blocked by cottonwood seed in the air obtaining trapped in the fins by the draft going with the condenser. The unit to be cleaned and restarted also though the unit had actually recently been cleaned.

The refrigeration cycle

If you had actually a instance that said “High head push fault” carry out you understand what was yes, really happening in the an equipment and what might cause it? Let’s testimonial the refrigeration cycle whereby it will be much easier to recognize the resources of a high head pressure fault.


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Refrigeration cycle illustration


The refrigeration cycle relies on the regulations of physics because that refrigerants going with a phase readjust from high press liquid to low push gas and earlier to a high push liquid. So exactly how does this high press liquid actually cool itself? The prize lies in the thermal growth valve (TX, TXV, TEV). The controls the pressure drop indigenous the high come the low push side of the refrigerant cycle. The growth valve is basically a constriction that the refrigerant line that accomplishes a press drop across the valve. By meaning if you have actually pressure top top one next of a valve and the valve is letting liquid move, climate the liquid on the other side the the valve will be in ~ a reduced pressure.

Expansion (drop in pressure) that the high push liquid refrigerant will flash evaporate roughly half of the refrigerant before it being introduced to the evaporator. Think around water that boils more quickly when you’re at altitude (lower atmospheric pressure). It’s push that is hold the refrigerant in a liquid type and once that push is released that mixture desires to boil.

Because this mixture is not having heat added or removed at this time, the phase change from fluid to saturated liquid/gas will reason the mixture to radically autumn in temperature. This is because energy in the type of warmth is being converted come a new form or power to support part of the refrigerant in gaseous form.

Heat is shed to the development of the gaseous form of the refrigerant. This heat loss is called the heat of evaporation. It’s the lot of warm needed to change a fluid to a gas. Girlfriend can include heat come the system to develop the warmth of evaporation (the burner including heat to boil water on a stove) or the heat power required can be pulled from the original mixture or its next site if the push is low enough and also there is no various other source. Due to the fact that the pressure is diminished the refrigerant is going come be required into a phase adjust and it will literally suck heat out that the mixture to do it causing a huge drop in temperature.

Refrigerants are just special compound or mixtures that exhibit very details phase alters at convenient temperatures and pressures. Plenty of liquids could be supplied as a refrigerant, however the boiling and also condensation properties of those liquids don’t work-related well under common cooling conditions or they are uneconomical to produce.

The development valve chin is not proactively accepting or rejecting warm (there will be part ambient warmth transfer if the valve is exposed). Once the press drops the mixture starts to boil and also the temperature drops together the heat of evaporation is extract to assistance the saturation mixture the liquid and also gas. Now the low pressure side that the development valve is the place where you have truly cold refrigerant.

At this suggest in the bike the waiting conditioner wants to put this cold refrigerant v a warm exchanger and also transfer warm from the waiting in a room earlier to the refrigerant. The currently low pressure, low temperature liquid/gas refrigerant mixture is sent right into a warm exchanger called an evaporator. It’s dubbed an evaporator due to the fact that the heat air indigenous the an are is pass by a pan over coils containing the refrigerant and the warmth in that air is moved to the refrigerant bring about it to extensively boil and also change fully back to a gaseous type (saturated liquid/gas come a superheated present of vapor).

Remember the the refrigerant is at a much lower pressure now. Like water boiling at a reduced temperature in ~ high altitude, so will certainly the refrigerant boil or readjust to a gas in this lower pressure environment and in the procedure soak increase heat. Remember, heat constantly moves from warm to cold. So warm is naturally lugged from the warmth air come the cold refrigerant with the interface of the coiled pipe (usually copper pipe dubbed the coil). The air increase colder because the heat has been removed. The refrigerant vapor is now holding that heat and carrying it earlier to the compressor to begin the cycle all over again.

High Head press Fault: A Vicious Cycle

Back come the initial question: What is a high head press fault?

A high head push fault is identical to a high temperature fault. over there is a straight relationship in between temperature and also pressure for a substance in gaseous form (from thermodynamics). If temperature goes increase then push goes up if the volume is constant. If you understand anything around the container of the gas and also if you know the pressure you can number out the temperature. If you know the temperature, you can number out what the pressure is. In this case pressure is provided as the method to recognize the state the the liquid after it has been compressed. If its pressure is high climate so is that temperature.

High temperatures are a killer to compressors. If that goes too high it will literally breakdown the lubricant because that the compressor and also the compressor will destroy itself with metal on metal wear.

After the low pressure vapor coming into the compressor is compressed, its temperature rises since the press rises from the mechanical work done by the compressor. Power is included through mechanical compression and also the an outcome is a high pressure, high temperature vapor. You space converting electric energy come mechanical power to thermodynamic power ready to it is in unleashed again.

A high head pressure fault establishes if the vapor return to the compressor is too hot and the succeeding compressed refrigerant will additionally be hotter than normal. If there is also much heat in the refrigerant climate it’s feasible that the following step of placing it with the condenser to litter off that warmth will not completely condense the refrigerant right into liquid form. At that allude you have actually a devolving refrigeration cycle where the refrigerant never makes it completely to liquid type in the condenser prior to being sent out to the expansion valve. The expansion valve works due to the fact that you have actually high press liquid gift converted to a saturated mixture of gas and also liquid at lower pressure.

Therefore, girlfriend can’t put a gas with an growth valve and also get the refrigerant come cool down since cooling the the refrigerant occurs once pressure is released from a liquid and it start to come to be gaseous. If it’s currently mostly gas then no far-ranging expansion or flash cooling deserve to occur. Shortly no more heat will be soaked up and every one of the refrigerant cycle will certainly be in gas form. The compressor eventually overheats and destroys itself from rapidly boosting temperatures (getting hotter since heat is still coming from the an are as well as mechanical heat added by the compressors.)

So the difficulty with having high head pressure is that it is one indication that the refrigeration cycle is broken and there is no usage in trying to exercise it further. You are in a vicious cycle. The unit has to shut down prior to it destroys the compressor and this is why most modern systems have actually a safety and security cutoff in the instance of high head pressure.

What failure in stimulate to reason a high head press fault?

Ultimately a high head pressure fault is brought about by extreme heat in the system. The heat can be coming from a super hot room the you’re trying to cool. It might come native the buildup of warmth from a poorly functioning condenser can not to throw off the warmth the mechanism is picking up and many other reasons consisting of overcharging the refrigerant. Let’s look at several of these problems and also why they lead to a high head push fault.

Condenser Blockage

Most high head pressure faults will be on the condenser side of the system; the unit normally on the roof or outside the building. Among the main troubles is a physics fouling that the condenser fin which restricts air flow over the coils. If air isn’t moving well over the fins and coils then there won’t be as much heat transferred and therefore less warm is ejected from the system.

As outside temperatures rise or the inner load rises, much more and more heat will must be rejected. It’s possible to have more heat to disapprove than the condenser is maybe to litter off. This leads to higher temperatures and also therefore greater pressures in ~ the development valve. Much more heat end up in the increased refrigerant reduce the evaporator efficiency and also that leads to greater temperatures and also pressures of the vapor return to the compressor. It’s a negative cycle that only gets worse unless the warm load is dramatically lessened or the unit is closeup of the door down.

In the instance of our customer’s Liebert system, cottonwood seeds began to accumulate and also block the air flow across the condenser at some point causing the condenser come not store up together temperature rose and also a high head push fault shut down the system. Short cycling started as the reset itself a number of times before shutting down for great when approximately air temperature reached around 105 F.

Damaged fins

Other reasons of condenser inefficiency encompass damaged condenser fins. If you’ve been up close and also put her hands on these fin you understand they are fairly easy come bend. When they’re bent climate no air can flow over that section of the coil to reduce the all at once efficiency that the condenser and also therefore the condenser can’t refuse as lot heat. If the damages to the fins is too much it can dramatically reduce the warmth load the system can handle.

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We’ve seen examples where one overzealous maintenance person has actually directed high pressure spray across the fins and flattened entire sections. What started out together an operation to enhance the condenser performance by clean the fins and also coils finished up damaging and also reducing the condenser efficiency.