Evaporator Thread Size - Need Help

[mmiller]

Hello All,

First off, car is a 1978 280CE.

I am dealing with some AC issues. I just installed a new front shaft seal on the York 210 Compressor, and of course a new Receiver/Dryer. I was able to vacuum down the system to 29.5, and let it sit overnight. The next morning, the system was down to about 26. So it appears I have a small leak overnight. I rechecked all my hose fittings under the hood with a torque wrench. All good. I was using a TIF 'sniffer' to confirm all was sealed properly.

The next step was to install a small amount of refrigerant into the system, just enuf to get the compressor cycling. In the cabin, I was getting about 40F out of the vents, at a low ambient temperature of 70F. The cooling was good. I turned off the compressor, and turned the Climate Control 'Off'. I stuck my TIF into the dash vents, and the 'beeping' increased. OH CRAP. Without a second thought, my mind immediately told me Evaporator leak.

The next step was to pull the passenger side kick panels, so as to access the Expansion Valve. When the TIF probe was brought next to the Expansion Valve, no increased beeping. To be on the safe side, I checked the 4 fittings with the torque wrench; all was within specs. Next, I probed the sticky black sealant that seals the Evaporator Pipes as they enter/exit the Evaporator Box. More bad news on the way. The TIF jumped. More confirmation, at least to me, the the Evaporator has a leak.

To confirm all this, I ran the Climate Control Fan with no AC running, just fresh air. This should have removed any residual gas from the ducts. Then, fan off, and wait 5 minutes. The TIF probe was inserted into the ducts and indicated no gas. Then, I ran the AC on high with the probe in the ducts, and no rise in beeping. The Climate Control was then turned off. I waited about a minute and probed the ducts. A rise in beeping.

Here is my conclusion. There is a small leak in the Evaporator/Box. The leak is small enough that it only leaks when the refrigerant is pressurized. It is small enough that when introduced with blowing air, it is not even detected by the TIF. However, when the system is turned off, the residual pressure in the refrigerant line is bled off and is detected in the ducts.

Before I go any further, what am I misinterpreting in my tests and results? Where am I going wrong?

The next step is to isolate the suspected part, the Evaporator. To do this, the plan is evacuate the system and reclaim, disconnect the expansion valve from the Evaporator, put a vacuum on the Evaporator, and monitor for leaks. I will need to patch-together a coupling from the vacuum pump to one side of the Evaporator threads. The other side threads will need a pipe cap. So to sum it up, What are the threads on both lines IN/OUT of the Evaporator? To the best of my knowledge, the EVAP is the NLO Behr A0008304658.

But, one nightmare at a time! Before I am confronted with yanking the dash/console out of the car, and struggling with the Heater Case and Evaporator Assembly, I want to positively identify the 'fault'. I have been searching the Forum here and reading thread after thread of pertinent posts. Lots of good info and advice, which I fear I may need to follow.

Thanks for Your Help,
Mark