Case Study: Processing package units with and without Schrader cores
On June 20th, 2020, VTI received a five-ton package unit from a manufacturer in the HVAC industry without a refrigerant charge or Schrader cores. The manufacturer explained that their plant currently manufactures these and similar package units with the Schrader cores installed. Schrader cores prevent gas from escaping units after they’re charged with refrigerant, but they also restrict how quickly operators can load units with refrigerant in the first place.
To see whether VTI’s Schrader Core Removal Tool might help our customer process their HVAC units faster, we decided to “process” (evacuate and charge) the package unit they sent us both with and without the Schrader core installed.
We performed our first set of tests with the Schrader cores installed using a Welch 1402 vacuum pump (5.6 CFM). Our customer specified that they require a rate of rise test that is fifteen (15) seconds long, with an end pressure of less than 1500 microns (1.5 Torr). It took two hours of pump time before the unit passed the rate of rise test. After venting the unit and allowing it to rest overnight, we repeated the test with the cores removed. Using the same vacuum pump, the unit passed the rate of rise test after only 20 minutes of pump time.
While residual refrigerant may have marginally impacted the pump down time for the first set of tests, this second set of tests demonstrates that removing the Schrader core from the package unit dramatically reduces the amount of time required for processing.
To verify these results, we repeated our experiment using a different vacuum pump. With a Welch 1397 (17.7 CFM), we once again pumped down the package unit without removing the Schrader cores. Next, we removed the Schrader cores and pumped down the units for a second time. We attached a manifold to the pump, which consisted of two manual ball valves and a vacuum gauge in the middle. This allowed us to both measure the pump’s base pressure and isolate the pump from the vacuum gauge for a rate of rise test.
This new set of tests had several parts: time to reach below evacuation setpoint (500 mTorr or 500 microns), rate of rise test immediately after hitting setpoint, rate of rise at ten (10) minutes of evacuation, final pressure reading after 15 minutes, and rate of rise at the end of 15 minutes of evacuation. The data can be seen below in Figure 2:
This particular customer in the HVAC industry currently allows for up to 15 minutes of evacuation time. While contaminants commonly found inside coils from manufacturing may have been removed by several pump-downs, 15 minutes appears to be an adequate amount of time for evacuating with Schrader cores either installed or removed. Even at just ten (10) minutes, the unit would have passed the rate of rise test with or without its Schrader cores installed – even if just barely with the cores installed.
While evacuation is commonly the most time consuming part of processing a package unit, we also performed tests to determine the impact of cores on refrigerant charge machine time. To run this test, the units were thoroughly evacuated using the Welch 1397 and manifold setup from previous tests. With cores installed, machine time increased by over a minute, with the charge process alone taking an additional 78 seconds (121 seconds with the cores installed; 43 seconds with the cores removed).
For the tests with cores installed, we used VTI’s Schrader Core Tooling with core depressor installed. The tests without cores were performed using VTI’s Schrader Core Retractor Tooling (Figure 1). These tools both have a ¼” VTI O-Seal, which were terminated with PCU 250 series connectors for quick connect/disconnect.
CONCLUSIONS Using VTI’s Schrader Core Retractor Tooling to remove Schrader cores prior to processing package units dramatically reduces the total amount of time required to process those units. For companies sensitive to takt time improvements, this represents a significant increase in throughput without additional line space, labor, and equipment.