Diagnosis And Repair Of Problems With 1981 - 1983 Imperial Air Conditioning

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Question from Stan:

Where can one find the replacement hoses for these cars?


From Bob:

I don't know where you are located, but there are plenty of places here in Texas where you can get the replacement hoses. I have purchased the hose pieces separate from the metal fittings and bought the special fittings with barbed male ends on which to force the new barrier hoses. Then lock it on with a hose clamp and it is most satisfactory. The most expensive hose for these cars is the suction hose with end fittings for the TXV valve, Dryer and Compressor inlet If you want original Chrysler hoses try a dealer.

From Jack:

I just replaced my a/c hoses last year and found the parts in stock at AutoZone. just walked up to the counter and purchased them. They come in 2 assemblies, and really couldn't be any easier to replace. I think they were around $55 each. Be sure to buy a new receiver dryer $29 and gaskets (less than $10)

Question from Lawrence:

When I have the defrosters on it sounds like a door is trying to close!!! And when the AC. is on I hear the same noise, could the AC clutch be defective?? Does any body out there have a thought on this? I haven't started to diagnose this trouble yet. With the AC on I can hear the compressor coming on and going off. It will finally stay engaged, could this be from lack of use??? Is there a relay for the AC compressor?


From Paul:

In cars built during the middle '70s and up, the A/C clutch is suppose to cycle, not stay on all the time, unless the system is turned on to "Full". Even then, it will only stay on continuously until the system senses a predetermined maximum cold temperature has been reached. If the system is continuously cycling, and very quickly (like on-off-on-off)that means that the system is low on Freon. Your car probably has R-12 in it. That runs about $150.00 per pound. If the system needs more than 1 and 1/2 or two pounds of Freon, the A/C clutch will not engage at all. The system probably holds a total of 3 or 4 lbs of Freon. The A/C compressor is suppose to run and cycle when the defroster is on. Another common source of leaks is the compressor shaft seal.

From Phil:

Paul's post was right on the money...sounds like low refrigerant. Check the sight glass in the receiver-dryer for bubbles while the system is running (clutch engaged). The receiver-dryer is located on the passenger side fender-just follow the AC lines to it. You may have to clear dirt away from the top fitting to see the sight glass. Here are the common leak points for a 318 AC system: fittings on the expansion valve at the firewall, fittings on the receiver-dryer, condenser, and the dreaded evaporator. Over the years, I've had a number of 318 Mopars and every one of them has had leaks in those places. The condensers have usually failed in the same place: look for oil/dirt accumulation at the bottom front of the condenser on the passenger side. I have one to replace on my 86 Fifth Ave right now. One other source of leaks: the hoses. While 35 year old hoses hold just fine, some of the mid-eighties hoses have leaked R-12. Hoses will be softer than normal and covered with refrigerant oil and dirt...don't know why. Leaks must be fixed sooner or later...the only vehicle that I successfully maintained with a "can a year habit" was a 90 Dakota. It had a very small leak in the evaporator that started when it was about five years old. That went on for about 5 years until the evaporator failed completely. That's rare and I suggest you be prepared to spend some $ if you want AC. Once the faulty component is identified and replaces along with the receiver-dryer, a conversion to R-134 is probably the best way to go.

From Bob:

When you engage the defrosters, yes, a door does close--it will shut off air from the heater outlet and the dash outlets and put all the air to the windshield. It is designed to do that to give you maximum heat and air flow during humid and warm weather. Additionally, you didn't say how warm the outside temperature. If it's just pleasant and not hot, the a/c will cycle on and off. It's designed to do that. Some later systems use a "reheat" system where any time the a/c is on, the compressor runs. Increasing the temperature to warmer just admits more heat into the airflow but the compressor still runs all the time. Some engineers decided that having the a/c compressor on all the time made for more even humidity in the cabin area. When you cool air, you remove the humidity. I have several GM cars with automatic air conditioning and there is no vent position on the control panel. Even at full heat, the compressor stays on. You have to turn the system off and open the windows to eliminate the compressor running. Frustrating to me--I once wired a toggle switch under the dash to cut the compressor on a 75 GM product so I could get all the air out the dash vents. I soon melted contacts on the switch and had some very hot wires. On the plus side, both cars have well over 100K miles on them and neither have ever had the compressor off or any problem with the a/c. Maybe there's something to be said about the compressor running. Maybe it keeps lubricated that way.

Question from Richard (1981):

I need some help from the old pros on this list that may know the electrical system that operates the AC in a 1981 Imperial.  In a nutshell, I can't get power to the circuit for the compressor. I can bypass the switches and all the fuses that I can find, are good and the resistance of the Ambient Temp Sensor is 280 ohms which is perfectly within spec. I am missing something and I am to new to this car and just haven't had any luck figuring it out.  Anyone have any ideas????



From Bob:


Your compressor is run off circuit 18DB via the Low Pressure cut-out switch preceded by the Cycling Clutch Switch. If the fuses and the wiring are okay, you might just check the pressure in the system; if low, the compressor won't start. Both of these switches are located on top of the expansion, ("H"), valve.


From Kerry:

I bet you have a low pressure switch on top of the drier. If your Freon is low, the compressor wont run. they did this so you could not run your compressor with no freon and ruin it since the oil is carried by the gas.

To check your clutch, just run a test lead from the battery hot side to the clutch wire with the motor off. You should hear the clutch click in and you should NOT be able to turn the clutch by hand. MAKE SURE THE MOTOR IS OFF when you try this test. If that works, try bypassing the low pressure switch. If that is it, you need to fix your freon problem before you try and run the system or you will scrap your compressor.

From Dick:


The compressor has a cutout switch that will prevent it coming on if it is low on Freon. Check your Freon pressure with the system off - if you don't read at least 70 PSI or very close to that, the compressor won't run. This is to prevent ruining the compressor, since the lubrication depends on the Freon circulating.

This safety device is on most modern cars, by the way. I think it started being commonly used in the late 70's.

You can bypass this device - it is installed in the refrigerant line near but prior to the expansion valve, just jumper across the wires, but don't do this until you are ready to recharge the system, for obvious reasons. And, it goes without saying, FIND THE LEAK FIRST! AC systems don't lose refrigerant unless there is a leak.

Follow-up from Richard:


I have charged the system and got it cooling. I drove it about 10 miles and it cooled fine. I parked it at home for about one hour and when I left in the car again, the compressor won't come on. I have bypassed both the low pressure switch and the compressor cycling switches and still no luck. I can run 12v to the clutch on it will kick in and the system will cool. The pressure on the low side is within acceptable limits (@ 115 psi while not running) and has been holding pressure, with little or no change in the last two weeks. I a have pulled the control unit out of the dash and verified that the switch that controls the compressor is functioning properly. The circuit is open if the switch is off or if the heater is on and in all other positions, the circuit is closed which should engage the compressor. The problem is apparently upstream of the in dash control unit because I am not getting any voltage to the switch for the compressor. I have checked all the fuses and they are OK. What could I be missing??




From Jack:


You may have a clogged expansion valve.


From Bob:


Okay - you have pressure and by-passed both refrigerant control switches. The problem is either a defective clutch coil or somewhere in the electrical system. Measure voltage to the clutch with the system turned "ON." If no voltage then back-up into the electrical system until you do find voltage. Voltage is supplied to the Push-Button Switch thru a 30 amp fuse, (fuse no. 4), from the ignition switch. Is your Ignition switch defective, loose connection?? Turn the key On then Off and read the voltmeter for this check. The power to the Compressor clutch is in wire C2, 18DB coming from 20 amp fuse no. 16 to the On - Off switch to the 8 way connector which is located in the harness on the right side of the engine. Look for wire C2 18 db with a tracer.


From Dick:

If you have a Factory Service Manual, the place to get your electrical tracing information is there. You are going to need one to maintain this car, as it is very complex electrically.

Just follow the 12 volt supply wire backwards with a test light until you find the disconnect. The problem could be in your ignition switch, but don't start replacing things willy-nilly, you will spend a lot of money and time on this sort of an Easter Egg hunt. Get the manual and track down the problem on paper first.

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