Cleaned the TDL on 13 October, 2015 and the dewpoint from the TDL was close to the dewpoint from the Edgetech chilled mirror. During the clear flights from Grand Forks, ND to Great Falls, MT and then from Great Falls, MT to Everett, WA the TDL did not respond to atmospheric moisture changes above some altitude. Cleaned the TDL again on 9 November 2015, but the TDL had the same response. Figure 1 shows an example of the TDL not responding to changes in atmospheric moisture before 75000 seconds on the 12 November 2015 flight.

Figure 1: Temperature, Edgetech Chilled Mirror dew point, and TDL dew point for the 12 November 2015 flight.

Bad fitting just inside the TDL case on the inlet line causing a leak. Figure 2 shows the location of the bad fitting. Pressure test shows TDL plumbing cannot hold either a vacuum or pressure. Pressure test with the chamber only shows chamber can hold 13 in. Hg with no change over 30 seconds. Pressure test with chamber and TDL outlet shows plumbing can hold 13 in. Hg with no change over 30 seconds.

Figure 2: Picture of the inside of the TDL after replacing a bad fitting.

Replace short metal tubing piece with the bad fitting with a longer length of plastic tubing with swagelock fittings attached. Turn the tee at the bad fitting location around to give more room for the plastic tubing to come from underneath and attach to the fitting in the TDL case (Figure 2). Tested the whole TDL instrument for leaks and the whole TDL instrument holds 13 in. Hg over 60 seconds with no change.