Imperial Home Page -> Repair -> Air Conditioning -> General
Great Tip From Elijah:
Running your air-conditioner at least once a week during the colder months is critical to maintaining its functionality. One of the neat things about my '71 Imperial which has standard heat and air (as opposed to the Auto Temp II system) is that it has a switch built into the system which runs the A/C compressor for five minutes whenever the heat or defroster is turned on (unless, of course, the ambient temperature is below 32 degrees F). This feature helps insure that all A/C seals and components stay lubricated during the winter months. I'm sure other years of Imperials have this same feature as well.
Question from Elijah:
Say I want to fix my air conditioner. I want to replace all the seals, right? And I want to evacuate the system, and then I want to replace the old R-12 with a new type of refrigerant. As I understand it, that's it in a nutshell.
Generally, I don't believe in replacing ALL of the seals. Replace what is necessary. Hoses don't last forever, if one is bad then the other will soon follow.You need:
o Set of TUBING open-end wrenches. DON'T USE STANDARD OPEN-ENDS!
Tubing wrenches are more like box wrenches with a small cut-out so that you can slip them over the tubes. They are more secure on the fittings and allow proper torque to be applied WITHOUT rounding the nuts.
o R-12 Manifold/Gauge set
o Vacuum pump
o Refrigeration oil (Use nothing else. All mentions of oil in this document refer to refrigeration oil)
o R-12 supply, or a substitute refrigerant (good luck) I don't recommend 134a for R-12 systems. It's too darn inefficient.
Use a substitute for R-12 if you can't get R-12.
o Dry nitrogen (welding supply)
o Liquid leak detector
o Safety glasses
Wear safety glasses and heavy gloves when working on a charged system, handling components under pressure, and when disassembling the system (especially when opening the first connection.) Having liquid R-12 spray onto your hands is a very unpleasant experience. I'd imagine it would be much worse in the eyes!
(Yes, some idiot I know REALLY WELL has gotten liquid R-12 (& R-22) on his hands, when trying to take a short-cut.) Don't try to prove that you're dumber than I.
Start by identifying leaks, if there is no pressure in the system, pressurize it to about 70 PSI with the dry nitrogen.
Identify leaks by liberally squirting each connection with the leak detector solution. Pay close attention to spots that look oily or have an accumulation of dirt, which may indicate accumulated refrigeration oil. Check any dirty/oily places on the condenser and compressor. If the compressor is leaking, remove and replace seals. (I'll scan, OCR, and turn the relevant RV-2 service manual pages into htm, if anyone is interested.)
When you open the system, discharge it completely, wait a few minutes for dissolved refrigerant to out gas from the oil, then slowly open the necessary connections, pausing to release any pressure.
DISCHARGING: Connect the gauge manifold. (See below) Open the blue hose valve slightly to allow gas to escape. Capture and measure any oil. You will need to add that oil back into the system. Actually, you should use an approved recovery system that will suction the R-12 out of the system and store it into a tank. Of course, the system usually has leaked all the refrigerant out, so you usually don't need to worry about this step.
When the system is open, cap or plug any lines that you will not be working on. If you are working on the compressor, cap the lines that attach to it, and plug the compressor ports. Remember: Dirt is Bad.
(Remember when you tracked mud onto mom's carpets? Well a little, tiny bit of dirt in an A/C system is worse. Instead of a standing in the corner, you will get to do the job again and replace the expansion valve, or compressor reed valves, or who know what else?)
Always replace the receiver / drier if the system needs to be opened.
Always use new gaskets.
Systems use one of two gasket types, flat metal sheets, and O-rings. The compressor, later model (74+) H-valves, later evaporators and condensers (80ish+) use the metal gaskets. Everything else is O-rings.
If the compressor needs service, carefully drain it, and measure the oil that you drain. When reinstalling, add back only that amount of new oil.
When reassembling, oil all connections and gaskets. It helps them to go together more easily, to seal completely, and makes O-rings last longer.
(They don't dry rot.)
Once re-assembled, connect the manifold to the system and the vacuum pump to the manifold. (Blue hose to the valve connection on the back of the compressor. Red hose to the valve connection on the muffler in-line with the connection on the front of the compressor. Yellow hose to the pump. Open both valves.) Pull at least 28" for at least 60 minutes. More vacuum for longer is better, since it removes more moisture. Moisture combines with the refrigerant and forms acids. I had to replace the H-valve in my 83 Imperial because Chrysler did not properly evacuate the system, and the insides of the aluminum H-valve corroded and plugged the liquid passage.
Close both valves and turn off the pump. (In that order) Watch the vacuum gauge for 20-30 minutes. If the pressure rises, you have a leak.
Find that leak. To find the leak either: 1) coat fitting with refrigerant oil and see if the leaking stops. 2) Charge to 70 PSI with dry nitrogen and check for leaks with the leak detector solution.
Now you are ready to charge. If you can get refrigerant, connect the yellow hose to you supply, and turn on the tank valve. Slightly loosen the yellow hose's connection at the manifold to let a little gas escape.
This purges the air and moisture from the yellow hose. Retighten the connection. R-12 charges as a gas. Most R-12 substitutes charge as a liquid. Check the instructions for the product you are using.
Weigh your tank. If you are using small cans, I think 3 cans is the exactly correct amount for single unit systems.
If charging as a gas:
Hold the tank upright (usually marked "This end up for GAS." Open the blue hose valve and let the gas flow until it stops. (Gauge should read close to 70-75 PSI.)
Start the engine, A/C on and set to HIGH. Adjust the blue hoses valve so that the charging pressure is no more than 80 PSI. Charge until the correct amount is pulled into the system. (Check the weight of the tank.)
If charging as a liquid:
Hold the tank inverted (usually marked "This end up for LIQUID." Open the red hose valve and let the liquid flow until it stops.
Check gauge pressure. Close red hose valve. Start engine, A/C on and set to HIGH. Adjust blue hose valve open to increase suction side pressure by usually no more than 10 PSI. (The idea is to slowly draw liquid from the tank, but for it to vaporize while it is in the blue hose, so that no liquid hits the compressor, where bad things happen when liquid refrigerant enters.) Oh! You want to pull liquid from the tank because the substitutes are usually mixtures with different boiling point. Pulling liquid pulls them all in equal proportions. Pulling gas pulls mostly the one with the lowest boiling point, then the next when the first is gone, then then next, and so forth. Not what you want to do. Stop charging when the appropriate amount (by weight) is pulled in.
Close all valves. Stop A/C and engine. Remove hoses. Here's a little hose removal tip from some who learned the hard way. Hold the metal tube of the hose end in against the fitting while you unscrew the connector.
Once the connector is completely unscrewed, pop the tube off. If you don't do it this way, you usually get quite a lot of leakage while disconnecting the hoses. On the high side, that mean oil and liquid refrigerant spray out.
Cap the valve ports.
Enjoy the coolness.
If you can't get refrigerant, evacuate the system as described above.
Test with vacuum, as described above. Instead of charging with refrigerant, connect the yellow hose to the nitrogen tank, vent the hose by opening the nitrogen tank's valve and loosening the hose connection at the manifold to let some gas escape. This purges the air and moisture from the hose. Tighten the connection, and open both valves to let some nitrogen into the system. Close both valve once positive pressure is viewed on the gauges. You can put as much as 70 PSI into the system. If you'd like, you can also leak-test the system.
DISCONNECT the clutch wire from the compressor to prevent compressor operation. Have a licensed tech evacuate the nitrogen and charge the system.
Bonus: The system has been properly evacuated and charged with dry nitrogen. Since the system was clean when you put the N2 into it, when he evacuates it again, any tiny amounts of moisture that may have been entrained in the oil will be removed as well as the nitrogen. The N2 charge helps "sweep" contaminants out.
Personally I always do a sweep charge to make doubly certain that nothing but pure refrigerant and refrigeration oil remain in the system.
To work on automotive AC systems, you need some fairly expensive equipment.
The manifold gauge set is not too expensive (about $75 for a good set with hoses), but you really also need a vacuum pump, which has to be adequate to pull a real vacuum, like less than. 01 ATM (AKA 30" at STP), and I also make a lot of use of a good leak detector. These last two items will cost you around $700 or $800 new from your local Snap-On Man. If you haunt the older AC repair shops, you can probably find an old Vacuum pump that does not have the recycling ability that is now required at the shops, and if so it should be cheap, but the leak detector is going to be expensive.
As for what to do with your system, you need to have it pumped down and then recharged with a partial charge of R-12 so that the technician can find the leak with his detector. When you know what is leaking, you will know the next step. Likely, it will be only one seal, and the most likely is the shaft seal on the compressor. The second most likely is one of the hoses or connections. Evidence of leaking is often visual - if you see an oily mess emanating from one of these locations, you have very likely found your leak. You can fix any of the above yourself, but you would still need the pump and manifold set to evacuate and recharge the system.
If you've read my previous posts on this subject, you know my feeling on converting the car to a different refrigerant, I won't burden you with my harangue again.
This page last updated November 20, 2002. Send us your feedback, and come join the Imperial Mailing List - Online Car Club