Solved Odd A/C Problem ****SOLVED****

[TechGuru]

I'm usually the A/C guru around here but this has me stumped, I've never experienced this on anything before.

The a/c is perfectly cold, most of the time, I've noticed lately my compressor cycles a lot while cruising down the highway and and creating enough load to feel it in the vehicle movement.

I hooked up my gauges and the low side is normal but the high side is hitting 450psi at 2800rpm.

Normally I would think clogged orifice tube but when I've experienced those on the past the low side was low. This is acting more like a over charge, but it was last charged 2 years ago when I replaced the compressor and it was fine the last 2 summers and nothing has been added since.

Condenser fan roars at cold start up and after sitting running in the heat for a while so I'm pretty sure the fan clutch is good.

As I said before it's cold "most of the time" there are 1 minute periods where it starts to get warm I'm guessing once the high cut out switch has been triggered and it takes a min for the pressure to go down enough to come back on...

I looked it up, high cut off is at 430psi and cut on is at 285psi. Just in case anyone coming across this thread would like to know, the low cut off is 25psi and the low cut on is 44psi.


According to this http://www.chiltonlibrary.com/content/images/Ford/S3N/S3NC0007.pdf that high of PSI is normal if it's 120 degrees out. It was about 100 degrees when I tested.

 

[blabla]

Too much oil? (Just a wag)

 

[TechGuru]

Too much oil? (Just a wag)

But how would that just now be a problem? The system has not been opened (caps not removed for anything) in two years...

I did notice something weird, as I revved it up to 2800rpm the low side went down as it should but then it rose some then went back down, that makes me wonder if someone installed one of them variable orifice tubes in it.

 

[blabla]

Just another wag: what if the condenser is partially plugged? The pressure would rise above the cutoff before adequate refrigerant had been cycled - essentially reducing the capacity of the system. I think the net result would be increased cycling. Like I said, just a wag as AC systems are not my forte.

 

[Joe in NY]

Could just be the compressor retiring and clogging the orifice strainer or condenser..

 

[BrooklynBay]

I would suggest that you check the orifice tube for debris, then replace it, and refill the system. Make sure that there's oil in it too.

 

[plasticseng]

Is there plenty of airflow across the condenser? Too little airflow will result in high pressure on the high side with somewhat normal low side pressure.

 

[Donystoy]

Was the refrigerant properly weighed into the system when it was worked on two years ago. If it has worked fine until now, and you have no mechanical noise my gut feeling is that there is an issue with the compressor again. Not sure on the type of valving used on these type of compressors. I know that r134a does run at higher pressures than r12 did but am not familiar with expected head pressures. With automotive there are a lot more variables involved so 450 pounds at 2800 rpm might be acceptable. I remember the old Chrysler V twin compressors back in the 70's use to run at a lot higher head pressures than other types at that time. From having worked on A/C and refrigeration systems for many years before I retired, when encountering sudden pressure changes it was generally caused by an issue with the valving or unloaders in the compressor. Have never seen a metering device cause a sudden change in pressure either. Even if one of the fans were to stop the change should be more gradual.
Also could you have an issue with the dampers? Have you checked to make sure the hot water valve is off and there is no flow. Not sure where the water rad is located with respect to the evaporator but could be also an area to investigate.

 

[TechGuru]

Was the refrigerant properly weighed into the system when it was worked on two years ago. If it has worked fine until now, and you have no mechanical noise my gut feeling is that there is an issue with the compressor again. Not sure on the type of valving used on these type of compressors. I know that r134a does run at higher pressures than r12 did but am not familiar with expected head pressures. With automotive there are a lot more variables involved so 450 pounds at 2800 rpm might be acceptable. I remember the old Chrysler V twin compressors back in the 70's use to run at a lot higher head pressures than other types at that time. From having worked on A/C and refrigeration systems for many years before I retired, when encountering sudden pressure changes it was generally caused by an issue with the valving or unloaders in the compressor. Have never seen a metering device cause a sudden change in pressure either. Even if one of the fans were to stop the change should be more gradual.
Also could you have an issue with the dampers? Have you checked to make sure the hot water valve is off and there is no flow. Not sure where the water rad is located with respect to the evaporator but could be also an area to investigate.

These use scroll compressors, no valving that I know of in them, they create a pulsed output.

I may need to do the folded magazine test on the fan.

It's perfectly cold when sitting parked at idle for even a hour. Then when I start going non-stop I can tell the compressor shuts off and the air starts to get a little warm then about a min later the compressor will come back on and it will be freezing cold.

 

[Donystoy]

Might be a tough one to diagnose. Not sure if these compressors are of the variable displacement type or not. If it is it will have an unloader valve assembly. Still is puzzling why it only happens while going non-stop. One would think that stop start traffic would create more overall heat.

 

[TechGuru]

Might be a tough one to diagnose. Not sure if these compressors are of the variable displacement type or not. If it is it will have an unloader valve assembly. Still is puzzling why it only happens while going non-stop. One would think that stop start traffic would create more overall heat.

Scrolls are not variable displacement as far as I know.

 

[Donystoy]

There are scroll compressors on some vehicles that do have variable displacement. In fact some do not even have a clutch so the compressor runs all the time and just bypasses when no cooling is required. Probably another attempt to cut weight and improve mileage. I am sure not crazy about that type as I like to be able to electrically switch off the compressor especially if it is starting to fail. I tried to do a Google search on our compressors to see if they were variable displacement but could not find any info. I do not believe that they are. Good luck solving your issue.

My A/C has not worked for a couple of years. I have dry eyes and the cool air irritates me but I hope to get back to trying to get it operational again considering that it is suppose to be a long hot summer.

 

[TechGuru]

I have dry eyes and the cool air irritates me but I hope to get back to trying to get it operational again considering that it is suppose to be a long hot summer.

Try putting your cool air on floor instead of the vents blowing it in your eyes...

 

[Donystoy]

Just wondering if you finally got your issue solved with your a/c. I finally got around to working on mine since they are calling for a very hot summer. Mine was just a bit low on charge so I will have to try to find the leak. What I did discover was that at idle with close to a proper charge the system continued to operate properly. If I increased the rpm's of the engine, the suction side would start to lower a bit and eventually shut off on low pressure control. What I am wondering is that your system might be just a bit low on refrigerant. When I added a small amount of refrigerant, this cycling stopped. I did play around with mine a bit by slightly over charging and then putting it back in my tank to study the high side pressures at different speeds and charges.
Sure was easier with the older systems when you charged at 2000 rpm's and added refrigerant until the sight glass was clear.

 

[Joe in NY]

You

Just wondering if you finally got your issue solved with your a/c. I finally got around to working on mine since they are calling for a very hot summer. Mine was just a bit low on charge so I will have to try to find the leak. What I did discover was that at idle with close to a proper charge the system continued to operate properly. If I increased the rpm's of the engine, the suction side would start to lower a bit and eventually shut off on low pressure control. What I am wondering is that your system might be just a bit low on refrigerant. When I added a small amount of refrigerant, this cycling stopped. I did play around with mine a bit by slightly over charging and then putting it back in my tank to study the high side pressures at different speeds and charges.
Sure was easier with the older systems when you charged at 2000 rpm's and added refrigerant until the sight glass was clear.

Procedure calls for weighing in charge for most accurate.

For topping off do as follows:

1) Open driver window
2) increase idle to 1,500 RPM
3) Set fan to MAX, Air source to Recirculate, 60*F or Coldest temp setting, Panel Vents only
4) System should cycle on and off due to low pressure cutout *Unless 90*F or higher*
5) Cycle ON/OFF times:

70*F: 30 - 65 seconds ON | 13 - 23 seconds OFF
80*F: 45 - 100+ seconds ON | 2 - 17 seconds OFF
90*F: 100 - ∞ seconds ON | 0 - 5 seconds OFF

From the 2002 Ford Workshop Manual Explorer Mountaineer Vol 2/2

 

[Donystoy]

Thanks for the info Joe. That is basically what I did after Googling it although nothing was found with the cycling time info. Will check mine again when the temperature warms up this weekend as I could have a bit of an overcharge. Nice to have the proper info for the Explorer. I set the rpms with shim material since I did not want to disturb the set screw (working alone).
I know the proper way is to weigh in the refrigerant but my scales decided to quit working. Not crazy about removing the initial charge as there is always some loss from purging etc. If the system had been bone dry then I would have had to find the leak, repair it, evacuate and weigh in the correct refrigerant charge. The only prior service that I have done to this in 15 years of ownership is replacing the receiver-drier that corroded from the inside about 7 years ago. It did last stop functioning a couple of years ago from the small loss of refrigerant but I never got around to repairing it. Not my daily driver and seldom have the a/c on when at highway speeds.

 

[TechGuru]

seldom have the a/c on when at highway speeds.

Wha?!?!?!?!

City, State: Hamilton, Ontario

Ooooooo....

My weather:

 

[Donystoy]

Wha?!?!?!?!

City, State: Hamilton, Ontario

Ooooooo....

My weather:

We do have hot weather into the 80s & 90s and humid frequently in the summer but nothing like what you have. A/C in the winter I just open the window.

 

[Donystoy]

We do have hot weather into the 80s & 90s and humid frequently in the summer but nothing like what you have. A/C in the winter I just open the window.

 

[TechGuru]

****SOLVED****

The problem was actually being caused by LOW refrigerant. I believe there may be a little moisture in the system that was turning to ice due to low refrigerant levels which caused a blockage.