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The Gentleman's Express: Tech-Tips from the JIOC

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Heater Temperature Control, Interceptor II and III (Bulletin JE73-1)

Author: Jensen Motors, Inc


After an initial settling in period, it may be found that the heater will produce only hot or cold air, with no intermediate temperatures. In such cases, it will benecessary to carry out the following checks and, if required, adjust the control.

Checking Procedure

  1. Remove the vacuum tube from the ‘Ranco’ water valve and connect itto a vacuum gauge. Care must be taken to avoid damaging the water valveplastic, should the tube be stuck.
  2. Startthe engine to ensure normal vacuum exhaustion from the main tankand leave at ‘idle’.
  3. Turn the temperature control through ‘green’ until the white linecoincides with the commencement of the orange ‘warm’ sector. Take a vacuumreading. SHOULD BE 4-5 in Hg.
  4. Turn the control to the mid position of ‘warm’ and take a vacuum reading.SHOULD BE 5-1/2 -- 6-1/2 in Hg.
  5. Turn the control to the commencement of the red ‘hot’ sector, and takea vacuum reading. SHOULD BE 9-11 in HG.
  6. Finally, turn the control through the full travel of ‘hot’ and take a vacuum reading SHOULD BE 12-14 in Hg.If the readings in the ‘warm’ sector are substantially less, particularly at the commencement of the orange sector, proceed with the following adjustment:

Adjustment Procedure

  1. Loosen the console panel and tilt sufficiently to give access to the backof the temperature control and, in particular, to a small brass set screw. NOTE:The set- screw, which faces downwards, is located at a point adjacent to theretaining ring of the plastic control housing, furthermost from the panel face.
  2. Using a screwdriver, turn the set-screw clockwise by not more than 1 /4 turn, then recheck the vacuum readings as already described. If necessary, repeat the procedure until the required vacuum readings are obtained. NOTE: Generally, it will be found that the car, with 5 to 10,000 miles completed and producing hot/cold extremes only, might have settled to 2 -- 2-1/2 in Hg at the commencement line of the orange ‘warm’ sector, but due to cam contour will remain near the correct vacuum reading in the red ‘hot’ sector. Under no circumstance should the set-screw be adjusted to a point giving in excess of 5-1/2 in Hg at the commencement line of the orange ‘warm’ sector.
  3. Finally, secure the console panel, and refit the vacuum tube to the ‘Ranco’ water valve.

Yours very truly, JENSEN MOTORS, INC
M. J. Hazlewood, Service Engineer

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