Air source heat pump trouble shooting

Error one: High pressure alarm and solution

 

High pressure alarm is the common error in the air source heat pump system, there two types error in general, 1^st is water piping system, 2^nd is the electrical system. The solution should be decided after the error reason is clarified.

 

The error is because of electrical system if it alarms right after the unit is energized and compressor is not started yet; the error is because of water system, if the error comes after the unit runs for few minutes or a while.

 

We can find the corresponding solution after the reason is clarified.

 

I. Reason and solution for the HP alarm in water system

It is more often to have HP alarm in water system, let’s explain it first:

The 1^st situation: There is HP alarm within 3 to 5 minutes after the unit is switched on, regardless the current water temperature, that is to say, there is alarm right after the compressor start, the high pressure value is higher than 3 MPa in the pressure gauge, it is mostly because of there is block in the water circulation system.

The water level in water tank should be checked first, then check the valve is open or not before the water circulation pump, then check is the Y strainer (the Y strainer stopper should downward, it should be noted during installation) blocked before the water pump, then check is the air released in water pump, is the water pump working normally or not? It is allowed, check the water circuit is normal or not in the water tank. Most of the problem will be solved after the above steps checked and corrected.

The 2^nd situation:  The unit pressure is normal when the water temperature is relatively low. There is HP alarm when the unit runs for certain period or several hours, and the high pressure is higher than 3MPa. The main reasons are: water pump flow rate is not sufficient, circulation pipe length is too long, or too many elbow, scale on heat exchanger.

The water pump parameter is usually mentioned on the rating label of the unit, the pump should be selected properly, if the pump is too small, the flow rate will be not enough, it is easy to have HP alarm; there will be energy waste if the water pump is selected too big. The circulation pipe between the unit and water tank, distance no more than 3 meter, better to keep in 1.5 meter, and adopt 3 to 4 elbows (45℃).

If there are too many elbow, the water resistance will be too big and water flow rate insufficiency and HP alarm could be caused due to it. There is another reason of HP alarm, scale in heat exchanger, if the water quality is poor, and calcium and magnesium ions is much in water (TDS meter can check), the scale formation is fast. Generally, if the TSD is above 200, the unit will have HP alarm after operation of around 1 year.

If the HP alarm is because of the scale, professional scale detergent should be used to clean the heat exchanger. There are two ways of cleaning, one is to use interior circulation that is suitable for the hot water system below 10 tons, another one is exterior circulation that is suitable for hot water system above 10 tons. The dosage and period should be controlled well to avoid getting hole on the heat exchanger.

For the small hot water system, for example, below 10 tons, just keep the water level over the circulation inlet/outlet, and put professional scale detergent or vinegar into water tank and run the unit, to clean the unit and water piping. For the bigger hot water system, the interior circulation method needs to drain huge amount of the hot water in the water tank, it wastes water and time, so exterior circulation method is recommended.

 

 

As shown in the picture above, steps as follow: Close the gate valve at the water circulation pipe to cut the circulation circuit, and add one water make up tunnel at the water inlet at the circulation water pump, and put the water outlet pipe of the unit inside the water make up tunnel, and put the professional detergent in the tunnel with water at the percentage specified in user manual, then run the unit and have circulation to clean the heat exchanger.

No matter which cleaning method is used, how to know the cleaning result? For the interior circulation method, we can observe the water temperature and high pressure gauge during cleaning, when the water temperature is above 50 ℃ and the HP is below 2.5 MPa, it means the heat exchanger is cleaned already. For exterior circulation, take the water temperature sensor out of the water tank and put it in the water make up tunnel, and observe the water temperature and high pressure gauge, when the water temperature is 55℃ and pressure is below 2.5 MPa, it means the heat exchanger is cleaned well.

Not to use oxalic acid or diluted hydrochloric acid, for it is easy to get hole on the heat exchanger and pipe due to strong corrosion.

 

II. Reason and solution for the HP alarm in electrical system

1^st situation: If there is HP alarm right after pump is energized and no start of pump, fan, compressor, mostly it is because of the failure of water tank temp. sensor, high pressure switch or PCB.

Solution: First check the water temperature displayed is the same as actual water temperature or not, if the difference is too much, then replace the water temp. sensor. There is one case happened, the displayed water temperature is 20 ℃, but the water is too hot from the water tank, and the HP alarms after the unit is switched on. If the water temperature displayed is same as actual water temp., then try to short connect the high pressure switch at the PCB, and power on again to test, if there is no more alarm, it means the high pressure switch is failed, if there is still alarm, it means there is failure of the high pressure control chip in PCB. If it is high pressure switch failure, then replace the coil of the high pressure switch, if the problem is still there, then replace the high pressure switch from the refrigerant circuit, and have the system vacuumed and charge refrigerant again.

2^nd situation: there is no regularity in the high pressure alarm, there is HP alarm both in low water temp. period and high water temp. period, and the pressure value is not high when there is HP alarm, it means the PCB should be replaced due to the failure of HP chip in PCB.

 

Error two: Low pressure alarm and solution

The are two situations for LP alarm.

1^st situation: There is LP alarm, and the LP displays normal when the unit is running, and above 0.1MPa, it means the LP switch error or PCB error.

Inspection method: Short connect the low pressure switch, and start the unit to test, if the LP alarm still remains, then it is because of the PCB, if the LP alarm is cleared, it means the LP switch is failed, inspection and replacement should be done accordingly.

2^nd situation: There is LP alarm when the unit LP is below 0.1 MPa during unit operation, it is because of refrigerant is not enough or no refrigerant.

Inspection method: To check the leakage point and weld the leakage point well, then vacuum it and charge refrigerant.

 

Error three: Error of no water make up in water tank and its solution

 

For the air source heat pump water heater system, no water make up is a common error, there are two reasons, one is pipe and water pressure, another is the electrical control system error. Inspection method as below:

1.       If the water makeup does not work when the water makeup valve is manually opened, the reason could be 1 water pressure is not enough. 2 water supply valve is closed or the valve is jammed 3 if there is floating ball in the water tank, it could be the floating ball is jammed, and no makeup water can flow in.

2.       If it is the water makeup does not work automatically, and it works with manual operation, the situation is little more complicated, and can be classified as below:

1^st situation, take out the water level sensor all over the water surface, and the water makeup works with such enforced action. The reasons are:

1 Water does not reach the temperature set for water makeup condition ( Normally the automatically water makeup water temperature is set at 50 ℃)，water make up works by enforcement, taking all water level sensor above water surface. The water is at certain water level in the tank, and the water temperature does not reach the water makeup temp. setting, it does not makeup the water.

2 There is scale on part of the water level sensor terminal, the instrument does wrong code or wrong water level. The water makeup does not work in such condition, which can work by enforcement, taking all water level sensor out of the water surface, and the instrument shows no water. It is caused by the scale on terminal.

2^nd situation: There is no water makeup even the water level sensor all over the water surface, the reasons are:

1 The instrument is in “OFF” status;

2 The solenoid valve core is jammed, or the solenoid valve coil failed;

3 No power supply to the solenoid valve

If it is found there is no power supply to the solenoid valve, then check the water makeup signal of the water level relay at the control system of the unit, if the water level relay does not send the water makeup signal, then it is because of the failure of the water level relay or there is no output signal from the PCB, and the water level relay or the PCB should be replaced.

Error four: water tank overflow error and its solution

There are two reasons for the water tank overflow in the air source heat pump hot water system, one is the water piping error, another one is the electronic control system error, the inspection method as below:

1.       There is water overflow even the unit power is off, the reasons and solution as follow:

1 Check the manual water makeup valve is at “OPEN” status, then check if there is a floating ball in the water tank, the floating ball is jammed or not at the open status.

2 Check if the water pressure is too big, if the voltage is too high, the solenoid valve spring can not get the membrane back at right position, and water is not blocked.

3 then check if there is block at the membrane of water makeup solenoid valve, and water can be held, or the valve core is blocked due to scale when it is lifted, and not able to get back after power off.

4 If the water tank overflow is caused by continuous return water from water return inlet, it could be there is block at the membrane of the water return solenoid valve, and water can not be held, or the valve core is blocked due to scale, and the indoor cold and hot water is connected or the mixing valve core damaged, and water overflows due to the cold water get into hot water pipe and enters the water tank through return water pipe.

A Y strainer must be fixed before the water inlet of water makeup solenoid valve and return water solenoid valve, otherwise, it is easy to have dirty or scale on the membrane and cause water overflow.

There is another special condition for the water overflow, the water does not flow in through the cold water inlet, it gets in the water tank from return water tank continuously, and the return water temp. does not rise, it could be that the hot water and cold water pipe get connected or one mixing valve core damaged at indoor, and the cold water gets into hot water pipe, and flows into water tank through return water pipe and causes the water overflow. The feature is that the water flow into water tank from return water pipe for this problem.

There is one hot water system case, it is in a 50 rooms hotel in tourist area, the tourist season is obvious, the occupation rate can be 100% in peak season, and it is no more than 10% in off season (winter). 8 tons hot water is selected. The user switch of the air source heat pump water heater is switched off in off season, and install the electric water heater in room, as the user though the power consumption is too high. It happens that there is hot water in some room, and no hot water in some other room, and there is water overflow from water tank in the peak season. It is found that the cold water gets into the hot water pipe through electric heater, as the electric water heater is not turned on in peak season, it is cold water in it, the it gets into water tank through hot water pipe and causes water overflow. The solution is to switch off the air source heat pump water heater in off season, and close all the water inlet and outlet of the electric water heater in peak season.

2.       There is no water overflow when the unit is power off, and there is overflow when the unit is energized, the reason and solution as below:

1 The wrong water level signal is caused by the scale on the middle and high water level terminal or the middle high water level sensor wire is broken. The water overflow is caused by the continuous water makeup due to the solenoid valve is always in power connected status by PCB or water level relay and gives water lack signal even the water tank is already full.

2 There one more situation, the indoor cold water and hot water is connected or the mixing valve core is damaged, and the cold water gets into hot water pipe and enter the return water pipe, and the return water temperature becomes lower, and the water return solenoid valve automatically open, and causes the water overflow.

 

Error five: evaporator frost and its solution

 

The heat pump water heater frost is common in winter, but if the defrost can not be performed properly, the heating effect will be seriously impacted, the inspection and solution as below:

First check the setting is correct or not, the defrost start time, start temperature, defrost period, defrost stop temperature is reasonable or not. The defrost start temperature is 2~4 ℃， defrost period is 30 to 45 minutes, and defrost stop temperature is 10 ℃ in general factory setting. Inspect those setting is reasonable or not first, and then check the next steps.

There are 8 situations of evaporator frost:

1.       Evaporator bottom part frost

It is mostly drainage is not smooth at drain pan, it will be all right after the defrost manually with hot water and clean the dirty. When there is frost on the evaporator, do not try remove the frost with hard tool to avoid copper pipe damage or even refrigerant leakage. The best way is to clean it with hot water.

2.       Equal frost on both side of evaporator, and no defrost

1 Check the defrost temperature, or put the defrost sensor into frost, it can be confirmed that the defrost sensor is failed if the defrost temperature is above 5 ℃, then replace the defrost sensor after the defrost with hot water flush.

2 If the compressor works normally, operate the reversing valve, or directly energize the reversing valve, it can be confirmed that the reversing valve coil is failed if there is no sound of pull in from the reversing valve, and no sound of refrigerant flow; it is the reversing valve jammed if there is sound of pull in but no sound of refrigerant flowing, and evaporator frosted, then replace the reversing valve.

3.       Defrost can be performed when there is frost, but defrost is not clean, not completely done, or there is frost at one side and no frost at another side, the solution as follow:

1 The defrost stop temperature setting is too low or the defrost period is too short, it will work after adjusting the defrost stop temperature and defrost period accordingly.

2 The defrost sensor position is not reasonable, it will work after placing the defrost sensor to the place with most serious frost.

4.       Frequent frost in short time

1 First inspect the defrost temperature is normal or not, if the defrost temperature displays normal, in the condition of below 0 ℃, inspect the ventilation is good or not around the unit, clean the object around the unit and flush the evaporator, and reasonably extend the defrost time and increase the defrost stop temperature.

2 Frequent frost on the unit, and pressure is relatively low at pressure gauge, defrost manually with hot water, and inspect the low pressure gauge during heating, it is confirmed that the refrigerant is not sufficient or refrigerant leaks if the pressure is lower than normal value (with reference of similar unit).

3 The unit fan motor is damaged or the air flow rate is not enough, for example, the fan blade is damaged or the fan motor power is relatively too small.

5.       Frost on one side or two sides frost is not equal or partial area frost on evaporator.

This situation is caused by the refrigerant is not equally distributed, and mostly because of a certain pipe is blocked, the solution is to move the defrost sensor to the place where it gets frost first and not easy to defrost, or replace the copper tube and vacuum and charge refrigerant accordingly.

6.       High pressure protection during defrost process

This is because of the defrost stop temperature is set too high, it will be all right after adjust it properly, and it is generally set at 10 ℃.

7.       Low pressure protection during defrost process

This is caused by the block or the opening is too small when the expansion valve flows reversely, the expansion valve should be adjusted or replaced, please follow the specific adjustment method mentioned in the manufacturer’s user manual, different model has different adjustment parameter.

8.       It defrosts even no frost

This is because of the defrost start temperature setting is too high or the defrost sensor is failed and causes wrong action, only needs to adjust the defrost start temperature or replace the defrost sensor.

 

Q&A: High pressure alarm and anti-freezing liquid etc.

1: Why the unit still works when there is HP alarm with the unit?

A: There are two possibilities of this problem, one is there is HP alarm on PCB, but no unit stop function interacted; another one is the PCB, high pressure alarm and unit stop interaction chip is failed, even there is high pressure alarm in instrument. The PCB should be replaced regardless which situation it is.

2. The unit is just started, pump is normal, and the high pressure gauge immediately rotates 180 degree, and have high pressure alarm in a while, what is the problem?

A: It should be because of the air is not released completely in the water pump, all the water pump should have air released before operation.

3.       Heating with air source heat pump, closed system, can the tap water pressure be directly used for water makeup?

A: Yes, but make sure the pressure is above 2 MPa.

4.       There is frost on from the liquid distributor head to evaporator and evaporator part near the liquid distribution pipe during the unit operation, why?

A: It should be because of the liquid distribution is not equal, it is normal if there is slight frost and can be defrosted, if the frost is heavy and it can not be defrosted, it may because of the refrigerant is not enough or there is refrigerant leakage.

5.       Should anti-freezing liquid be used for the unit in Hebei area? And the percentage?

A: This should be confirmed according to the local lowest ambient temperature in. The percentage should be prepared according to the user manual, how many percent of water, how many percent of anti-freezing liquid all described in the user manual.

6.       There was a HP alarm, and I clean the unit with oxalic acid, now it works well, should the PCB be replaced?

A: Not necessary to replace the PCB now as it works well after cleaning with oxalic acid, and it is not the problem of the PCB, it is because of the scale in heat exchanger, and it is already cleaned.

It is better not to use oxalic acid, it is strongly corrosive and slightly toxic. No matter what type of detergent is used, the unit should be cleaned again with clean water after the washing with detergent.  

7.       What will happen if the air is not released? Should air be released if there is no HP alarm?

A: It would cause water flow rate insufficient if air was not released, even there was no HP alarm, the unit operation pressure would be higher than that in standard condition, and it’s more easier to have scale on heat exchanger.