FAQ - High Discharge Superheat

For this instalment of Frequently Asked Questions we are going to focus on just one question that is asked regularly in an effort to reduce some of the confusion around the issue of superheat. While the Question is often about specific error or default codes, the underlying issue needs to be addressed.

Q: What do I do if a Temperzone unit cuts out on a High Discharge Superheat?

A: Firstly, the relevant fault codes for this are 9 on the UC6, and Hi-dSH on the UC7 and UC8. If you have come across a unit that has locked out on a Discharge Superheat fault, it is a good starting point to know what the ideal Discharge Superheat at standard cooling operating conditions should be (15-25K). With the latest Temperzone UC Controllers, obtaining the Discharge Superheat is now at the touch of a button.

If the Discharge temperature is too high, say 85°C or higher, it is highly likely that the evaporator is being starved of refrigerant. The most common cause of a starving evaporator is an undercharged system.

When dealing with pre charged split systems, a typical system will be factory charged with refrigerant for a certain interconnecting pipe length. Temperzone pre charge all split systems for a 10m pipe length. Unfortunately some installers guess what the actual interconnecting pipe length is and often will leave a system under charged.

Another possible cause is a refrigerant leak. Other causes of high Discharge Superheat are a kinked or restricted liquid line, a restricted filter drier, a restricted Accurator piston or Accurator strainer or an Electronic Expansion Valve (EEV) under feeding the evaporator. Restricted condenser air flow can also contribute to high Discharge Superheat. That of course will be the indoor airflow on reverse cycle (check the indoor unit filters and coil).

To check the superheat, reset and test run the system. Observe the Discharge temperature and Discharge Superheat via the units UC Controller. If you are working on an older model without a UC6, UC7 or UC8, measure the discharge temperature half way between the compressor discharge port and the entry into the reversing valve. Then, measure the liquid line pressure and convert on your PT Chart to temperature. (For R410A use the “Bubble” or “Liquid” table on your PT Chart). Discharge temperature minus the liquid line pressure converted temperature gives you the Discharge Superheat.

There is also low Discharge Superheat to consider. The most common cause of low Discharge Superheat is flooding to the compressor. That condition will more than likely be associated with an Electronic Expansion Valve over feeding the evaporator. It could also point to an Accurator or check valve issue.

Discharge Superheat above 45K will trigger a High Superheat Fault on the temperzone UC Controllers.

Discharge Superheat below 10K will trigger a low Discharge Superheat fault on the temperzone UC Controllers.

The Unit Controllers Trouble Shooting Guides are also incredibly useful and can be found on page 107.

Temperzone takes is Technical Support very seriously. Not only do we ensure that everyone who handles Tech Support calls are fully trained but we also spend an enormous amount of time updating our Service Training Manual regularly. We are committed to supporting everyone who installs and services both our Temperzone and Hitachi units.

If you would like to receive a hardcopy of the latest Service Training Manual, please email Mark Howcroft at with your postal address. Or click here to download a copy and keep it handy on your tablet or computer.