I believe there is a difference between the pressures that the A/C system will be exposed to when considering R12 and R134. I want to have the evaporator pressure tested locally. My understanding is R134 runs at higher pressure. I would like to know at what pressure does R12 run, and at what pressure does R134 run.

I have not made the decision yet on which I am going to run yet. I am aware of most of the changes in switching. I am just looking to get the evaporator tested at the higher pressure, so the box can get mounted to the firewall at the body shop. The rest of the decisions will come in the next couple of months.

 

Pressure difference is not that high between 12 and 134a, best to do a leak test under a vacuum. Coils can pressure test fine but a test under a vacuum is the best way to leak test a refrigeration or a/c system.

 

The evaporator in a working system is going to be much lower pressure than you want to test at. I tested mine at 225 PSI but hear of people testing at 300 PSI. The setup I was using for testing was not safe over 225 so I stopped there. If you don't have nitrogen then use a real good filter dryer on your air compressor and go as high as your air compressor will go. I personally never use anything other than nitrogen.

 

I am taking it to the shop that redid my radiator. They are an a/c shop too. Older guy that has worked on these for years will do the work. I just wanted to make sure I was asking the right questions. I will need to ask if he can do a vacumm test on it. I was thinking it needed to be a complete op system to test vacumm. I quests if he has the right fitting he could. I can definately check with him, what his capabilities are.

I'll send the rest to Classic Air, but I can't wait for an 8 week turn on the evaporator and box right now.

 

I have three Evaporators, so I should be able to find a good one. I wasn't happy with the boxes I had and picked up a really good one last night. I just need to be careful when cleaning it, so I don't remove this stamp.

 

There isn't much of a difference in pressures within the evaporator since it is on the low pressure side, behind the expansion valve, where the internal pressure is around 30-50 psi, depending upon the ambient temperature.

Now the condenser is another thing as it is on the discharge (high pressure) side of the compressor. Again, pressure is directly proportional to temperature, so in a very hot environment (Arizona) the pressure will be higher than in the frozen tundra of the north. The discharge pressure can range from around 200 to over 300 psi.

 

The evaporator is not going to leak in a vacuum if it holds over 200 PSI of pressure. If it has a hole it will not matter if is in a vacuum or under pressure. It will only change the direction the leak flows. With pressure it will blow out and show up with soap bubbles or under water, if under vacuum the bubbles would be on the inside and not seen.

 

Do not use soap bubbles for vacuum test, flaws in fittings and piping, especially elbows can pressure test good but leak in vac. Shaft seal is also a good example. If component or system can hold 29" of vacuum you are assured of a leak free and dry system. Jensenracing is correct on using nitrogen for test as moisture in system will cause acid and freeze up at TXV.

 

Eric,

Where did you get your gaskets/seals for the evap box to put the two pieces together and mount to the firewall?

 

no gasket/seal to mount the unit to the firewall. At least not from the factory. I used to work for Classic Auto Air and we always pressure tested the evaps to 300psi of nitrogen. I still restore these parts. Here are a couple of videos I made of an ac unit I restored for a 1970 442. Pay no mind to the title.

 

I used 3M strip caulk in the recessed area in the outer box and then pressed it to the firewall. That is very close to the same thing the factory used. The inside heater box don't use anything. It just seals against the firewall pad.

Different subject but I also used the strip caulk to hold the vapor barrier to the door that is between the door panel and the openings in the door shell. I believe whatever they used on the vapor barrier is the same thing they used on the A/C box to firewall.