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Ac repair question

I am having a issue that I cannot find any info on surfing the internet. Similar-but not my situation. I have a 2010 Chrysler Town and Country Touring 4.0L and my freon became low. Discovered a small leak at a connection point on one of the rear lines that I will be repairing but want to make sure I can resolve the other issue first before spending time and money on the leak.
When adding freon it will hold a charge for several days-enough to blow cold air. Problem I can’t figure out is while monitoring the manifold gage (before and after adding freon) the low and high side will rise, then the fan turns on in front of the condenser and then both pressures lower. Then the fan turns off and both pressures rise again. This whole process takes about 40 seconds and it never stops. Even when I added freon to the proper PSI (for the current ambient temperature at the time) both the low and high side continue to rise and fall about every 40 seconds. The pressures that it would rise and lower to were:
low side would rise to about 35 and the high side to about 250, then the low side would lower to about 22 and the high side to about 150.
Any help would be appreciated.

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I’d expect pressures to drop when the fan kicks in. The ‘condenser’ is ‘condensing’ the Freon better when the fan is on.

That is why an a/c shop checks pressures with the car running at high rpm AND a BIG fan blowing air across the compressor.

Time to bring in the pros, in my opinion.

You probably need a new compressor but 8 years is a bit early for it.

The pressures are dropping when the fan kicks in. Through repair manuals and info found online I have been able to diagnose some pretty tuff situations and have made many repairs on my own. Thought I would ask for some help on this one. Considering that the pressures are dropping when the fan starts does that give you any suggestions how to proceed diagnosing issue?

The PCM controls the radiator fans based on coolant temperature, transmission fluid temperature and refrigerant pressure. The fans should turn on at 250 PSI, then the power to the fans is duty-cycled to keep the pressure in a normal range. If the is a low load on the A/C system the fans may switch on and off.

The issue you have is a leak, isn’t it?

The leak I will be able to fix and it is a slow leak. Don’t want to spend time or money if it turns out I can’t figure out the constant raising and lowering of pressures. What do you mean by low load? Not enough freon in the system?

A low heat load, the amount of air flow and temperature of the air passing through the evaporator core. Normally the blower is set to high and the temperature to full cold when testing the system.

The cycling of the high side pressure is normal, this makes it difficult to judge if the system is full by observing the pressures. I always reclaim the refrigerant and refill with the amount shown on the label.

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And that’s exactly what I’d expect. Fan kicks in, extra cooling occurs, more Freon condenses, pressures drop. What don’t you understand?

What is happing is logical but from watching utube videos with people using manifold gages (to either diagnose and/or add freon) their gages were maintaining the same PSI readings. Not constantly going up and down like mine. I had seen it in multiple situations-when system was low, when adding freon, and when system was properly charged-PSI’s not going up and down. They did not have a large fan running in front of the condenser either. Therefore I thought I had something going on that shouldn’t be happening.

Don’t believe I mentioned it prior but the clutch stays engaged-not stopping and starting to coincide with the pressure increases/decreases. Could it be that my system is overcharged?

I am thinking that is the best thing to do at this point-to get my system evacuated, fix the leak, and then adding the amount of freon required for my van. Not adding freon until I achieve the appropriate low side PSI based on the ambient temperature. When you get your ac system evacuated does it remove the oil in the system also?

Some oil will leave the system while the refrigerant is being reclaimed but most of the oil settles to the bottom of the A/C components. Some oil may have been lost due to the leak, you may add an ounce of ND-8 PAG oil during the repair.

Appreciate everyone’s help. The leak is at a connection that can be taken apart with wrenches. I disconnected it and replaced the O-ring hoping that would fix the leak. I purchased all the O-rings for the whole system for my van and picked out the exact one that matches. Still leaks real slow. Tried tightening little by little and kept checking for leaks hoping at one point the correct amount of torque would be achieved-so not to overtighten and distort the O-ring. No luck. Eventually tightened it as much as I could and still leaks slowly. I am thinking air could have gotten into the system since I disconnected it to replace the O-ring so I was going to vacuum the system. Would vacuuming the system remove any oil?

The videos probably don’t have the cooling fans turning on and off.

That’s why I was thinking something wasn’t working properly. Do some automobile fans constantly cycle on and off when vehicle is not in motion-since airflow isn’t constantly blowing on condenser? All the videos I watched didn’t have a outside fan blowing on the condenser yet the pressures were not fluctuating like mine. I was thinking their vehicle fans must have been constantly running. Yet mine doesn’t.

As you have probably figured out by now, temperature and pressure are directly related. (Remember high school chemistry?) The pressures in the A/C system–particularly the high side–change in direct relation to the temperature of the condenser.

Some cars run the electric fans constantly when the A/C is selected. Some cars run the electric fans only when the compressor clutch is engaged. Some cars run the fans based on pressure in the high side of the loop. Cars with conventional belt driven fans, well, the fan is spinning all the time.

Constant variation of the high side pressure is normal operation for your car. Repair the leak, check the system performance and vent temp and motor on.

You want to have some fun? Next time you have gauges hooked up have a garden hose handy. Run the A/C and spray cold water on the condenser. The pressure will drop like a rock and the fans may never come on as long as your spraying the condenser.

Well that explains it then. Just so happened I must have watched several videos of cars that keeps the fan on while the AC is selected and mine must be one that is related to high side pressure. It was always when the high side reached 250 psi when my fan kicked on. Now that that is settled-onto the leak.
Question about that. Its at a connection point on a rear line right before the rear evaporator. It leaks behind the big nut and at the threads. Included picture with arrows showing points of leak. I took it apart and it had one o-ring in it. I purchased the whole AC system set of o-rings for my vehicle and picked out the exact one that matched the one I took off. Replaced it and tightened it back up. Recharged AC and it still leaked.
Read online there could be some crud in there so I took it apart and lightly sanded the inside surface of the fitting, then rubbed some brake cleaner on the inside of fitting. I then put another new o-ring on there. Recharged AC and it still leaked.
Then thinking I may have overtightened it and distorted the o-ring I figured I would loosen the fitting to the point where I could hand tighten it, then turn it a quarter of a turn at a time and check for leaks until I found just the right torque to compress the o-ring without smashing it. Ended up tightening it to the point that it couldn’t be tightened anymore and it never stopped leaking.
Wanted to see if anyone had any suggestions of what could be going on. If it can’t be figured out I am going to cut that connection out and replace it with a Dorman Line Splice For Aluminum Lines (which is the second picture I included).

Did you apply refrigerant oil to the O-ring prior to installation?


Yes, I forgot to mention that. Pag 46-which is what my van calls for.

The pressures will fluctuate not when the radiator fan turns on and off, but when the A/C compressor turns on and off. (And this is shown in some of the videos I have looked at.). Maybe the compressor in your vehicle is electrically tied to the radiator fan or you have a separate condenser fan. Not all vehicles have a separate fan for the A/C, so you won’t see this in every vehicle, but you will see it in every vehicle where the accessory belt drives the compressor.

The reason your compressor cycles on and off is the same as the reason your home A/C or refrigerator motor cycles on and off – because it’s cold enough. Once the heat exchanger is cold enough, the compressor will turn off until the heat exchanger warms up again from having hot air blown across it. The hotter it is, the longer the compressor will stay on, and vice versa.