Hi guys, I have replaced my entire AC system, with the exception of the relay, and the ambient temperature switch. The problem is that my compressor runs constantly it never cycles off. I am afraid its going to burn up my new compressor. It also causes it to overheat at idle. I replaced the entire cooling system too, so I know its not the water pump, or fan clutch, or radiator. I talked to a friend who said that there should be a thermal indication switch that turns it on and off but I read that the relay handles turning the clutch on and off on durangos. Does anybody know what actually tells the compressor to turn on and off? I know that my charge is good and that its neither over or under oiled and all the components are new. So I am thinking that its a switch or sensor problem.

Any help is appreciated.

Thanks!

 

Have you tried to replace the relay with another one to see if that helps your situation? Sometimes it's the small stuff that people overlook that started the problem. I am by far not an a/c guy but give it a few hours, you will have experts chiming in.

 

Actually funny thing is I just did that. Same problem. So, I am at square one again. I replaced the sensor that goes in the side of the expansion valve, didn't fix it. I swapped relays didn't fix it. The compressor has a connector for a rear AC system but its disconnected because mine doesn't have that. The only things I haven't replaced are the pressure switches and any other sensors/switches that I do not know of.

 

45autopete is the local A/C expert, wait for him to chime in and i bet you find the problem

 

With the way the temperature has been in the South and also here in Missouri, most compressors will not cycle at all. Just like a house A/C Unit, in this heat they will run and not shut off. You will not do any harm to the compressor because it is running all the time. The compressor has oil in it that helps keep it lubricated. Most likely, you will see when the weather starts to get a little cooler, your compressor will cycle off and on as needed. The Durango's are big boxes on wheels and it takes forever to cool one down and I bet that you have had your fan on it's highest setting to try to cool it off. It is like supply and demand, you are demanding a lot of your system to cool down your vehicle and in doing so, it is trying to supply all the cooling power that it has to offer. There is nothing wrong with your system and yes your engine will get hotter when at idle because it is relying on the E-fans to cool it down and when it is doing that, it is also pushing all that hot air off of the condenser towards your radiator which in turn will not cool the radiator until you start to get more air flow when you drive it.

 

I'm going out on a limb here but you said you replaced the Low side switch but what about the High side switch. Have you ran a pressure test on the high and low side ports?


Pete<----- I have never seen a time even when it was 110 outside that mine didn't cycle on and off. Now what you are saying makes sense however I have never seen it even one time other than a house but then again we are talking about a house (and coils which are not the same in size nor system), in fact I have never heard of a compressor on a house or business cycle on and off unless it was short cycling mostly due to high/low head or low R134. I'm going the other way on this one.

 

A house A/C unit works basically the same as our vehicles. When you set your thermostat to a certain degree, it keeps it there by cycling off and on. A vehicle is no different in that it does basically the same thing. A person is blowing warm air past the evaporator which has the expansion valve hooked into the system. What happens in the condenser is that this hot gas is cooled to a liquid state and travels to the expansion valve. As the refrigerant goes through the expansion valve it returns to a low-pressure gas. Then it rapidly cools in the evaporator. A fan blowing over the evaporator cools the air that eventually blows out of the vents. The compressor will not cycle if it is not cool enough in the interior of the vehicle, it will run until the evaporator gets cool enough that the pressure on the low side and high side will eventually cause the compressor to cycle. The evaporator when it is being warmed by the air flowing through it will cause the low side to stay low until it can get cool enough from colder air blowing through it and that will cause the low side to climb high enough in pressure to cycle the compressor. My Durango with the front and rear air will not cycle at all until the interior is cool enough, it does cycle at night time but during the day time with the sun beating down on it, it does not cycle at all.

 

I would put a A/C gauge on and see what your high side pressure is. If, you see your high side exceeding 350psi. You have a problem. I would put money on the high side switch being bad on your A/C system.

 

Pete, a house is controlled by a thermostat that has set points. Most of these set points are 1-3 degrees differential. Depending on the type and user interface that is needed.

When the hot set point is reached a 12 volt electrical current is sent to the furnace to turn on the fan. In return the Furnace sends a signal to the compressor and the freon runs through the evaporator thus giving you the cold air.

Now the compressor will NOT shut down until the low set point is reached on the thermostat.

Example: it is 72 degrees inside the house and you want it at 70. The thermostat has a 1 degree differential. This means the furnace turns on and compressor will run continuous until the desired temperature of 70 is reached. Once it is reached it cuts the signal, the compressor turns off and the furnace fan runs for about 45 seconds to help remove any frozen ice on the evaporator and make use of the already cold evaporator. Now when the thermostat hits 71 degrees it will kick back on. If you had a 2 degree differential then the inside temp would have to hit 72 before it would turn back on and so forth.

Now those 2 are very close in main operation but not so in makeup. Now in a car there is no set point. There is only high and low pressure. The compressor engages and starts to compress the fluid, once the high side solenoid PSI is reached the compressor is turned off. Now the pressure slowly falls until the low psi set point solenoid is reached. Then when the solenoid kicks on because the PSI is too low and the compressor starts climbing in PSI again to the high side, and over and over.

Now if the members compressor isn't kicking off and everything is good I would say the high side solenoid is not turning the compressor off. But again the only way to verify this and be entirely safe is to check the PSI readings on the High and Low side and see if you are in specs.

As far as your idea, I understand, however if you can't hold PSI at all then maybe the expansion valve is worn out allowing to much too fast to run through it so it can't hold the pressure, your low on freon, or the compressor is worn.


One last thing I would do,---->jbar<---- is take the harness off the compressor and make sure the clutch is working and not froze up. But again a PSI test is your best bet on figuring out what the issue is and the safest.

 

45autopete is correct on this issue. If you are sitting still on a very hot day your high and low sides will never reach there cut offs due to ambient temps. Which in return your compressor isnt gona cycle. If your compressor never cycles and there is a problem it is gona push the extreme pressure out the back port on your compressor or blow a line. If the compressor is under extreme strain due to high pressure (with the hood up you will hear the sound of your compressor change ). Make it simple throw some gauges on it and you will have your answer.