High Pressure Alarm (AL129) when Air to Water Heat Pump goes into defrost mode

Scope

This artile covers residential air to water heat pumps goes into defrost mode. the following models are covered by this article:

1. HSS030V2LM and LS
   
2. HSS060V2LM and LS
   
3. HSS080V2LM and LS
4. HSS030V3LM and LS
   
5. HSS060V3LM and LS
   
6. HSS080V3LM and LS
   

Trigger

The high pressure alarm is caused by a lower heat exchange either at the water side or air side of the heat pump. When it happens in defrost mode only, it's can be caused by:

1. Not enough heat heat exchange at the water side. When HP goes into defrost mode, it draws heat from a heat source (a buffer tank) and it dumps that heat into a heat sink (outdoor air cooled condenser). When buffer tank is undersized, or water flow is less than what it should be, the heat transfer from the tank to the air cooled condenser is less than what is needed. This causes the compressor to increase it's output pressure. Once that pressure exceeds it's ceiling value, HP controller throws an AL 129 Alarm.
   
2. Obstruction to heat on the air cooled condesner (could be restricted air flow path, or accumulated snow, or other things). This can also cause compressor to go overpressure which results in the same Alarm code.
   

Procedure

The above problems causing the AL129 Alarm are external to the heat pump. In order to accomodate them, we will need to make compressure work with its set of high and low limit of refrigerant pressure. To do that, please do the following steps:

Click on Prg Button.

Enter password:  Ask your rep for password.

go to M10 - Defrost Settings and press Enter to access sub-menus

Go to sub-menu Df04 - Defrost Param.

Change settings as followings:

1. Def. start Setpoint: This is the ambient temperature when defrost mode is intiated - recommended value of -1°C (default value - adjustable by user). Defrost is initiated when outdoor is -1°C or lower and ambient temperature sensor detects ice between the fins of the condenser.
2. Def. end Setpoint: This is the ambient temperature when defrost mode is terminated - recommended value of 12-15°C (default value - adjustable by user).
   

After entering the above setting, presse the Esc button to go back to M10 Main menu, then go to Df10 - Defrost Param

Change settings as followings:

1. Discharge Press .setP: This is the maximum allowed discharge refrigerant temperature. If Al129 is happening when this setp is 35 bar, lower it down to 32 bar. Run the heat pump, until alarm disapears (never set this value less than 30 bar pressure).
   
2. Diff.: This is a deadband value. Recommended value of 2 bar

• Related Articles

• Air to Water Heat is not switching to desired operating mode

  Scope This article covers residential air to water heat pumps with Carel Controller (Models HSS 030, 060, 080 V2 and V3 LS and LM). Trigger Customer is either unable to switch operating mode, or Heat Pump does switch to combined operating mode (like ...

• Geothermal Liquid to Water Heat Pumps going into freeze protection mode

  Scope This article covers GEO series Hydro Solar Liquid to water heat pumps: GEO040V1LM GEO060V1LM GEO080V1LM Trigger Default Heat Pump Parameters setup GEO series heat pumps with Titanium heat exchanger can be hooked up to both open (Lake, Pond, ...

• Enabling back up heat for Air to Water and Liquid to Water Heat Pumps

  Scope This article applies to our residential air to water and liquid to water heat pumps. Applicable model numbers: HSS030V2LM HSS060V2LM HSS080V2LM HSS030V3LM HSS060V3LM HSS080V3LM GEO040V1LM GEO060V1LM GEO080V1LM Trigger Backup heat is not ...

• How to change language for Air to Water or Liquid to Water Heat Pumps with Carel Controller?

  Scope This article covers the followings products HSS030V2LM / HSS030V3LM / HSS030V2LS / HSS030V3LS HSS0360V2LM / HSS060V3LM / HSS060V2LS / HSS060V3LS HSS080V2LM / HSS080V3LM / HSS080V2LS / HSS080V3LS GEO040V1LM / GEO060V1LM / GEO080 V1LM Trigger ...