This is a Refrigerants and Refrigeration lesson.
You'e called out to a local hotel, the manager says, "The lobby air conditioning unit is running, there is water everywhere, we have the thermostat set to 76F and it's 88F in the lobby."
Before you grab your tools and gauges, you locate the thermostat and verify that it is set to cooling. You also locate the air handling unit and see water everywhere, you can hear the blower running.
The outdoor unit is running and you put your hand over the condenser fan motor and feel hot air blowing from the condenser. You spot the condensation drain line and see water coming out of the drain. You decide to first check out the source of the water, and after opening the air handler you find this:
Wow!! As you walk back to your truck to get your gauges, you remember Module 3's HVAC training about refrigerants and what causes icing in an HVAC system. You think, "Restricted airflow, undercharge, or a bad metering device can all cause icing".
So before hooking up your gauges, you go back inside and verify the blower motor is running, the filters are clean (soaking wet but clean), and the coil is clean. You also realize that the ice restricts the airflow as well. You shut down the condensing unit and leave the blower running to thaw out the coil before you check the system pressures and temperatures.
Now might be a good time to get the manager and show him what you've found... this could take a while.
After all of the ice has melted you fire the condenser back up. You also remember that you should wait 15 minutes to let the refrigeration temperatures and pressures stabilize before making any measurements. (Obviously, you paid attention in Module 3 of your HVAC Training!)
You hook up your gauges and temperature clamp and here is what you find:
Being a great HVAC tech, you break out your notebook and record the system pressures and temperatures. Writing down the formula for superheat...
Superheat = Low Side Lineset Temperature - Saturation Temperature. So, 36.3F - 25F = 11.3F of superheat. Seems like the TXV is working as there is superheat. No wonder the coil is freezing, the saturation temperature is 25F. You wonder if the system is undercharged, because that can cause icing too.
You disconnect your temperature clamp from the suction line an put it on the discharge line and find this:
Subcooling = Saturation Temperature- High Side Lineset Temperature. So, 118F - 89.4F = 18.6F of subcooling. You think, "Superheat is good, and the subcooling levels indicate the system has enough refrigerant, maybe a little too much refrigerant. What else could it be?"
You check your superheat again and wonder what can cause the low side pressure to be so low. Obviously, the low side pressure is to low. So you decide to check the TXV.
To be continued.....
How would you go about checking the TXV? Is there anything else that could cause the icing?
by Ron Walker
You'e called out to a local hotel, the manager says, "The lobby air conditioning unit is running, there is water everywhere, we have the thermostat set to 76F and it's 88F in the lobby."
Before you grab your tools and gauges, you locate the thermostat and verify that it is set to cooling. You also locate the air handling unit and see water everywhere, you can hear the blower running.
The outdoor unit is running and you put your hand over the condenser fan motor and feel hot air blowing from the condenser. You spot the condensation drain line and see water coming out of the drain. You decide to first check out the source of the water, and after opening the air handler you find this:
Wow!! As you walk back to your truck to get your gauges, you remember Module 3's HVAC training about refrigerants and what causes icing in an HVAC system. You think, "Restricted airflow, undercharge, or a bad metering device can all cause icing".
So before hooking up your gauges, you go back inside and verify the blower motor is running, the filters are clean (soaking wet but clean), and the coil is clean. You also realize that the ice restricts the airflow as well. You shut down the condensing unit and leave the blower running to thaw out the coil before you check the system pressures and temperatures.
Now might be a good time to get the manager and show him what you've found... this could take a while.
After all of the ice has melted you fire the condenser back up. You also remember that you should wait 15 minutes to let the refrigeration temperatures and pressures stabilize before making any measurements. (Obviously, you paid attention in Module 3 of your HVAC Training!)
You hook up your gauges and temperature clamp and here is what you find:
Being a great HVAC tech, you break out your notebook and record the system pressures and temperatures. Writing down the formula for superheat...
Superheat = Low Side Lineset Temperature - Saturation Temperature. So, 36.3F - 25F = 11.3F of superheat. Seems like the TXV is working as there is superheat. No wonder the coil is freezing, the saturation temperature is 25F. You wonder if the system is undercharged, because that can cause icing too.
You disconnect your temperature clamp from the suction line an put it on the discharge line and find this:
Subcooling = Saturation Temperature- High Side Lineset Temperature. So, 118F - 89.4F = 18.6F of subcooling. You think, "Superheat is good, and the subcooling levels indicate the system has enough refrigerant, maybe a little too much refrigerant. What else could it be?"
You check your superheat again and wonder what can cause the low side pressure to be so low. Obviously, the low side pressure is to low. So you decide to check the TXV.
To be continued.....
How would you go about checking the TXV? Is there anything else that could cause the icing?
by Ron Walker