Retrotec Commercial 441 and 451 DucTester - Manual (Page 27)

Page 27 of 56
©Retrotec Inc. 2015
5.9 If no Results are displayed (--)
If the target pressure has been reached, but “--“ appears as a flow reading, the fan is running too slowly
to measure flow. Perform the following to get a duct leakage result:
1. Add the next smaller Range Ring.
1. Change Range Configuration on the gauge to match the Range Ring installed on the fan.
2. Re-adjust DucTester fan speed.
If the Range Ring installed is the smallest hole, there are no more Range Rings to install, and “--“still
appears:
1. Make sure Range Configuration on the gauge actually matches the installed Range Ring.
2. Check that the blue tube is connected to the gauge and then check that it is reading pressure – put a
finger on the open end of the blue tube and ensure that the Channel A pressure reading changes. If it
does not, then the tube is blocked or pinched.
3. Check that there is no blockage in the ducts between the DucTester and the register containing the
blue tube. To do this, move the blue tube to a different register and compare the reading on Channel
A to the original reading. If the pressures in the two locations are not similar, there may be blockage
in the duct system that needs to be removed.
4. Check that the DucTester is actually reading properly on Channel B. To do this, open up a taped
register to provide enough leakage to get a reading, and then increase the pressure to 25 Pa or 50 Pa
on Channel A. If the flow still reads “--” then the yellow or green tubes could be blocked or
disconnected.
If you are sure that the blue tube is reading pressure, there is no blockage in the ducts or tubes, and that
the DucTester is actually reading flow, and “--“ still appears, the ducts must be extremely tight; less
than 7 CFM. To get a rough result, cover half the inlet ring with tape which will quadruple the fan
pressure signal. Read the CFM, but divide the answer by two (since half the hole is open). If still reading
“--”, cover three quarters of the inlet with tape, read the CFM and divide the answer by four (since only
one quarter of the hole is open).
Instead of doing the calculations, an alternative is to set the Result to be Displayed” to “Pressure:
Pa”and look up the associated flow in Error! Reference source not found. (for 25 Pa induced duct
ressure).