superheat confusion few questions

[lees8110]

Hi all,
Im still learning the basics of AC and just have a few quick questions and queries if anybody would be kind enough to give me some answera or advice I wpould be very grateful,
The first being about superheat, I am working on a package heat pumpo unit, correct me if I am wrong, To measure the superheat, I am to connect my low pressure gauge on the compressor suction, my high gauge on the compressor discharge and my thermometer surface probe on the outlet of the evapourater (were the TEV bulb is) and I deduct the thermometer reading from my (comparitor converted temperature, vapour scale r407c) from my low gauge reading.
But the trouble is my low gauge is constantly fluctuating from 4 bar down to 2 bar as the condenser fan comes in and out, so I am unsure as to which reading do I take and while the this pressure is always changing so is my thermometer reading.
I am confused with this cos at college when I did this the pressure stayed the same on the fridge units we practised on.:rolleyes: Also do I need to, and how do I measure this with the unit in heating?(heat pump unit)
Can anybody educate me please:D

[Gary]

I am always uncomfortable explaining superheat to people because they tend to think that superheat is the first thing they should check. It is in fact the last thing they should check.

Every component in the system has to be functioning properly in order for the superheat to be right, and until everything else is right, any attempt to alter the superheat is probably the wrong thing to do.

[lees8110]

I am always uncomfortable explaining superheat to people because they tend to think that superheat is the first thing they should check. It is in fact the last thing they should check.

Every component in the system has to be functioning properly in order for the superheat to be right, and until everything else is right, any attempt to alter the superheat is probably the wrong thing to do.

The reason for me asking, Is not to diagnose a problem in this case, but too monitor the efficiency of a unit, as a service precaution to confirm the unit is running efficiently

[Gary]

The reason for me asking, Is not to diagnose a problem in this case, but too monitor the efficiency of a unit, as a service precaution to confirm the unit is running efficiently

Superheat will tell you nothing about the efficiency.

[Gary]

As you noted in your original post, the temperature and volume of air flowing through either coil has an enormous effect upon superheat. In order to properly judge superheat, these variables need to be stable and as close to standard design conditions as possible.

[D.D.KORANNE]

First stabilize condenser fan whereby high side pressure & in turn low side pressures will stabilize. Maintain design head pressure by properly timing cond fans .