1971 Mark III Questions

Hi Bill –
I have a Mark III 71. It is absolutely fantastic to drive and ride in the summer here in Sweden. But I have a few faults I tried to fix but do not really know what I should do.
There is cruise control but when I activate this, I get no function to keep the speed. There’s relay which I hear is activated when I press the activation when I stand still with the car. Could it be something electrical fault? Is there any deactivation via the brakes may have hung up ??? I have not been able to trace any vacuum leak. It would be very nice to have started this function again. The cruise control has never worked as long as I have owned this car (10 years).
The next problem is a little more teasing nature. The car’s equipped with ACC. AC pump is not operating because no gas is left in the system. In contrast, the temperature control function in a slightly odd way. When it’s really hot out there turned the heat on in the cockpit in full swing. When it gets cool the heating is switched off completely. Is this a common fault? What is the most likely error?
The car is as I said very nice to ride in but this is the wrong course draws down on comfort feeling.
I enclose a nice picture I took last year at a nostalgia petrol station here at home.
Thanks in advance
With best regards
Esbjörn
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Greetings Esbjorn –
That sure is a beautiful looking 71 Mark III.
The factory speed control and a/c units are nice options to have working on an older car. However if you or your mechanic are not familiar with these particular systems, proper diagnosis could prove difficult and even more so without the factory Shop Manuals. To answer your questions though many features are complicated and can be faulty in several areas and therefore need to be diagnosed using the shop manual. On these older Marks the speed control Regulators located under the hood with the speedometer cables attached to them are usually found to be at fault. The braking deactivation of the speed control when engaged is via the brake light switch located under the dash at the brake pedal linkage.
On your 1971 Mark (with the Automatic Climate Control A/C/Heat system) there is no provision to declutch the a/c compressor if the refrigerant charge is low or empty. The clutch will engage in all positions except OFF or if the ambient temperature drops below approximately 30-35 degrees F. There are very many causes of failures possible with the controls etc , and we do not know what if anything was done to the components in your Mark prior to or during your ownership. We find that most of these vehicles will however require rebuilding of the ACC boxes along with the blend door Servo and Switch assemblies and/or any of the several switches and relays. The shop manual along with good system operation knowledge, automotive electrical skills and refrigeration skills are necessary in order to perform meaningful diagnosis and to repair the many features of these older luxury vehicles. If we can help further with any needed literature or parts etc. please let us know.
Sincerely,
Bill