Chapter 7 – Maintenance
TestEquity 3007C Temperature Chamber
Page 7-11
Refrigeration System Charging Instructions
!
WARNING:
Repair of the refrigeration system must be performed only by a properly
trained mechanic who is experienced in repairing cascade refrigeration
systems. Do NOT substitute any component. Do NOT substitute refrigerants.
Improper repairs will void the warranty.
These instructions are intended as guidelines for repairing TestEquity chambers. Details such as
how to attach a gauge manifold are not covered. These are NOT do-it-yourself instructions!
R-404A High-Stage Charge
TestEquity does NOT recommend charging the system by relying on a clear sight glass only.
Although a clear sight glass generally means the system is fully charged, it can be misleading.
For example, if the system is charged on a cool day or with an empty chamber, it could be
undercharged for hot days or with a heavy load. The proper charging procedure is as follows:
1.
Repair any leaks before recharging.
2.
Attach a vacuum pump and manifold gauge to the suction and discharge ports.
3.
Evacuate the system to at least 100 microns. DO NOT GUESS! You must use a micron
gauge.
4.
Use a charging scale to weigh in 100 ounces (6.25 pounds) of R-404A.
5.
Verify the cooling performance as outlined in “How to verify the chamber performance”.
NOTE: If the Temperature Controller is cycling (Cool Light cycles on/off), the sightglass may
appear 1/2 to 2/3 full. This is normal.
R-508B Low-Stage Charge
1.
Repair any leaks before recharging.
2.
Attach a vacuum pump and manifold gauge to the suction, discharge, and expansion tank
ports. Attaching to the expansion tank is very important because it is otherwise very difficult
to evacuate the tank through the pressure regulator or capillary tube that is connects it to the
system.
3.
Evacuate the system to at least 100 microns. Do NOT guess! You must use a micron gauge.
4.
Do NOT put any additives in the system. Pentane is NOT necessary or desirable.
5.
Charge the system until the standby pressure is 142 PSIG. Allow time for the charge to
equalize as read on the suction and discharge gauges. This is 10 PSIG higher than the target
amount of 132 PSIG. See NOTE below.
6.
Verify the cooling performance as outlined in “How to verify the chamber performance”.
NOTE:
If the low-stage has been evacuated and recharged, the standby pressure should be
rechecked after 24 hours to make sure it is 132 PSIG. This is because the refrigerant mixes with
the POE oil in the compressor, causing a lower standby pressure than was initially observed. Do
not mistake this initial loss of pressure with a leak. After verifying that there is no leak, you may
need to top-off the charge if the pressure is too low.
