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1969 Mark III AC Questions

Hello Bill,

Just wanted to let you know that a while back I emailed you about the battery draining as a result of some electrical issue. You narrowed it down to the starter relay/solenoid. I replaced it and it solved the problem. Thanks for the help!

This is about the AC system. I had the entire system completely restored. Every component is brand new with the exception of the evaporator which was "restored".

Yesterday it was 90 degrees here so it probably wasn't the best day to charge the system for the first time.

In any event, here is what I've done so far:

Charged the system with 48 ounces of R-12. Shop manual indicated small cans in the day were in 16 oz cans and to use 3 for a complete charge. I double checked pressures today with an outside temp of 66 degrees. Low "suction" side was stabilized at roughly 35 psi. High "discharge" side was at roughly 165 psi and increased only slightly but stayed below 200 psi. Throughout the duration of this test, the pressures pretty much stayed at the stated numbers with only slight deviations (~1-3 psi).

This leads me to believe that the expansion valve and rest of the system (at least the components under the hood) are working properly. The compressor is engaged and is silent. No lines at the evaporator are icing up. The larger pipe on evaporator as well as the line to suction side of compressor is cold. The lower (smaller) pipe on evaporator is cold before the expansion valve and the opposite side of the expansion valve (small line that runs to accumulator) is warm. I'm not sure if either side of the TEV is supposed to be different temps. I have covered the TEV bulb at suction line with plumbers putty to make sure it is insulated.

With all this being said, the air coming out of the vents with the control lever on HIGH and temp control at 65 is only 60 degrees at idle. When I drive it, it gets to roughly 48 (on a cool day, on a hot day it stays at around 60). It's been my experience that the register air should be around 40 degrees and maybe even get a little colder once the engine RPM's pick up. I'm not familiar with the older systems.

Is it possible there are other issues such as mode door actuators that are not working properly ? When I change temp control to higher temps, heat does come out of the correct ducts but the AC is just not as cold as I think it should be. Please help!

Thanks,

Dan

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Hi Dan -

The a/c system on the 69-71 Marks will perform very well when all of the components are in good working order. Your outlet temperature of 60 degrees on a hot day of 80-85 ambient is too high if the controls are set at 65 degrees on High Range and the control system has responded accordingly with all features operating correctly. There are several items that are easily overlooked when diagnosing however that can contribute to this high outlet temperature. Assuming that all of the components that you have stated were restored or replaced etc. are indeed in good working order I can suggest the following for you to address. Your r12 charge of 3 lbs. is incorrect. The r12 charge for this system is 2 1/4- 2 1/2 lbs. max ( 36-40 oz ). The 8-12 ounces that you are overcharged can and usually will cause problems on hot and humid daytime outside temperatures. On those days of high outside temperatures and high humidity, the following two items must also be operating as designed. They are the vacuum controlled Water Valve and the Recirculation door device located in the air inlet system to the blower. The water valve module will receive vacuum to close the valve in the high cooling mode. Even if this valve is correctly receiving vacuum and appears to be operating o/k on the outside, it may not be sealing properly on the inside. It must be removed, examined and tested to be sure that it is completely sealing internally when vacuum is applied. I have seen some valves that have failed and cause a 6 degree rise to the outlet temp. on hot days. The recirc. door can be checked for operation by hearing the blower become louder when it opens and draws in air from the right cowl kick pad area. The correct operation as designed of the above two items is very important for all automotive air conditioners of this era on hot days. Another component to consider that you may have already checked is the thermostatic fan clutch that controls the engine cooling fan. On hot days it must engage at idle and low speeds in order to cool the engine and at the same time pull additional air through the a/c condenser. The above suggestions are good places for you to start and I hope that they will help you find an easy problem to correct.

Sincerely,

Bill