ACU Test Box (RH8851) - Rolls-Royce and Bentley Forums
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post #1 of 18 (permalink) Old 06-19-2016, 01:54 AM Thread Starter
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Cool ACU Test Box (RH8851)

Hi Guys,

I'm newbie to the Forum. My purpose for joining the forum is to learn more about these wonderful cars we're all in love with. As for me, I own a 1977 SW II LRF32027, ten years strong. Furthermore, it's my intention to make a contribution to the forum so that others may benefit from my experience. Having said that, I would like to introduce a project on the ACU Test Box that i've been working on for over eight years. I've finally completed it and here's what I've accomplished. A brief description: The ACU Test Box for 1965 thru 1980 Rolls Royce motor cars is used to test and troubleshoot various components in the A/C system such as the Servo and Servo Modules. A faulty Servo or Servo Module(s) will render the A/C system partially or totally inoperative. The full description and operating procedures are outlined in the Rolls Royce Shop Manual which is readily available in PDF form on just about every RR forums online. I've used the test box pictured on my 1977 SWII to troubleshoot an issue with the A/C system. The A/C blew cold for the first few minutes after switching on. Afterwards, the air would become warm to the point I had to switch off the unit. I then connected the test box according to the instructions in the shop manual. After following the procedures the test box indicated that the Lower Servo was out of calibration. I followed the procedures to successfully calibrate the servo. This was approximately eight months ago; as of this writing, the A/C system has been blowing cold air consistently. Needless to say, the test box has saved me quite a bit of time and money since I didn't have to take the car to a RR mechanic. Of note, you don't have to be mechanically inclined or be an electrician to utilize the test box. The instructions in the shop manual guides you through the whole process by asking "yes" or "No" questions or to confirm if voltage X is displayed on the Volts scale or a Servo Position on the servo scale. To confirm the accuracy of the test box I connected an original ACU Test Box (RH8851) to the AC system and accomplished the same testing procedures. The results were identical. You might say that I've validated the accuracy of the ACU Test Box pictured using an original ACU Test Box that has been recently calibrated. This is a really cool toy for those of us who enjoys working on the cars we love so much.

PS: I've uploaded a duplicate picture. I haven't figured out how to delete a picture from the draft. I also have lots more pictures of the project that I would like to share on the forum.

Please feel free to ask any questions you may have.
Attached Images
File Type: jpg ACU-TEST-BOX-1.jpg (87.0 KB, 67 views)
File Type: jpg ACU-TEST-BOX-3.jpg (95.5 KB, 42 views)
File Type: jpg ACU-TEST-BOX-3a.jpg (75.7 KB, 44 views)
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post #2 of 18 (permalink) Old 06-19-2016, 06:44 AM
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Is that a Crewe test box, or did you build your own?
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post #3 of 18 (permalink) Old 06-19-2016, 09:54 AM Thread Starter
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Hello jeyjey. I built it from the original wiring diagram.
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post #4 of 18 (permalink) Old 06-19-2016, 11:34 AM
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Nice piece of work!
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post #5 of 18 (permalink) Old 06-19-2016, 01:46 PM
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I see that your registration finally came through. Congrats!!

With any luck you managed to avoid the whole password changing bit as well.


The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth.
~ Niels Bohr

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post #6 of 18 (permalink) Old 06-19-2016, 07:49 PM Thread Starter
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Thank you. After several attempts I got through. Patience is the operative word here lol
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post #7 of 18 (permalink) Old 06-27-2016, 04:20 PM
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That is one beautiful piece of work! I am very impressed with the quality of the face lettering. How did you do that? Is this something you offer for sale?
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post #8 of 18 (permalink) Old 06-28-2016, 09:07 AM
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So brilliant work!


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post #9 of 18 (permalink) Old 10-25-2016, 01:39 PM
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That's cool! Where did you get the wiring diagram from? Is it available online?

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post #10 of 18 (permalink) Old 10-26-2016, 05:59 AM
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impressive tool indeed, well done!
Stupid question from my side: I have an 1985 Corniche (that's an SZ), would the SY box work on SZs?
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