Weird A/C pressure possible blockage

[biggy238]

Let me start be saying that I do have formal training for climate control, but have no real field experience.



My questions:

Is the orifice tube in the tube between the dryer and the low side port where the line has a joint and is slightly larger in diameter?



If the tube is plugged, what would have caused it other than parts of my a/c compressor?



History:



Well, last year I noticed the clutch wasn't cycling for the defrost. When it got warmer, the A/C was dead. I took a job at a dealership with the proper equipment.



I pulled the system down and checked for leaks. The system only pulled 1. 3 of 1. 9 pounds out. (from what i'm finding on here, this is normal. ) Pulled a vaccum. It did just fine.



We charged it, the a/c worked for a few minutes and stopped. We recovered it again. Pulled another vaccum. Still no sign of a leak.



Recharged it with dye in the mix. Ran it again. Never found any dye, anywhere. Gave up thinking it was the evap core. Also checked it with a sniffer.



Now, last night, I decide to try again, since I wasn't satisfied that it was the evaporator core. Recover the system. It pulls out . 48lbs and pretty well stops. I let it sit a while on . 48



Our machine has a 15 minute vaccum setting. I let it run through the 15 minutes, shut the machine off and check the gauges perodically. It held vaccum for 45 minutes. . never tried to move the needles.



We charge the system, I program the machine for 1. 9 lbs (1 lb 14 oz) and let it rip. I walk away again. in 1/2 hour, it only charges 1 lb.



I start the truck, thinking it will pull a little into the system. the low side pegs the gauge (over 120psi) and high side is sitting constant at 150 psi.



I think the orifice tube is plugged. 80 degrees ambient temp.



My questions:

Is the orifice tube in the tube between the dryer and the low side port where the line has a joint and is slightly larger in diameter?



If the tube is plugged, what would have caused it other than parts of my a/c compressor?

 

[B.G. Smith]

The orifice tube is in the line coming from the condenser to the ecvaporator or one of the connections therein. The receiver/drier is in the line going from the evaporator to the compressor (low side, suction) If the tube was plugged the low side should have gone below compressor cut off pressure, about 23# I believe. My first thought is the compressor has failed. When you charge the system the engine should be running with the AC on, this will lessen the chance of slugging the compressor with liquid refrigerant and damaging compressor valves/etc. The other scenario where the pressures would be high on both sides would be if the orifice tube has been removed from the system. p

 

[RVTRKN]

If you have a restriction at the refrigerant control (orifice) then your low side will cycle at the pressure your low pressure control is set at and it will short cycle, the clutch will disengage fast. You can bypass the low pressure control by jumping the two pins at the LPC and the clutch will never disengage and your low side will pull down into a vacuum. But I'll warn you not to do it for a long period of time, say no more than 2-3 min, its just a trouble shooting tool, if it has the ability too pull a vacuum, now you know your compressor has the capability of doing so.



The statement you wrote, as far as testing for leaks using vacuum, is a no no. If there is a leak you will pull in moisture with air when in a vacuum. If you can't get dry nitrogen and charge the system with 75 PSI "with the refrigerant recovered" and you lose pressure but can't find the leak, then the next best thing is to charge it with virgin R22 but do not run your system at all, and using a good refrigerant leak detector run your blower on low and put the leak detector in the airstream it should go off if the evaporator is leaking. The reason for the R22, is that R22 is more sensitive and will show up easier. This is the method I used to find my leaking evaporator when I could not detect the R134a, and that was with the best on the market detector. Once it is known were the leak is and is fixed, when evacuating (vacuum) put a drop light on the accumulator to heat it up, forcing any moisture out of the drier.



You must make sure there are no leaks and that the proper weight (amount) of R134a has been charged into the system, then you should see a restriction if its there. Moisture can cause a temporary restriction though. if there is a restriction the low side will short cycle the clutch and the high side can be higher than normal but if your stacking the refrigerant then it can be at or below the normal pressure. You should have a nice cold and sweating (not iced up) suction line if its running normal.

 

[biggy238]

Well... Thank you for your help.

We charged it, the a/c worked for a few minutes and stopped. We recovered it again. Pulled another vaccum. Still no sign of a leak.

Not entirely accurate on my part. However, pulling a vaccum on a freshly recovered system i'm thinking is a fairly common practice. What I was trying to commute was that while pulling a vaccum to rid the system of what contaminants it might have had, the gauges maintained their positions, which would indicate that there is not leak. It has done this 5 times now with no change in the outcome.



And with due respect, I personally will not be putting R22 into anything. Nitrogen, Yes.



One of my co-workers suggested that we go see a man today that has been in the biz for quite some time. He pulled a vaccum, charged the system and had me start the truck. The clutch engaged, and it pegged at 475psi on high side. He got a waterhose and started spraying the condensor. It immediately brought the pressures into check and the cab got cold. The clutch started cycling appropriately. We all agreed that the condensor was plugged up and not flowing enough air. This coninsides with what I noticed monday night, that the lines were both extremely hot while the compressor was operating.



On the way to work, I got caught in a rain storm and the windshield fogged. I kicked on the defrost before I thought about the fact that the pressure would spike. I turned it off and almost immediately and came on to work after wiping the windshield out.

After work, I pulled the four bolts and pulled the condensor out. I blew through it with compressed air to dislodge what I could, brushed it with a plastic bristled brush and washed it with a water hose. It went from being difficult to see though, to being able to see through it and see vehicles and objects though the fins. The fins are 90% clear.



We started the truck and kicked the A/C on. The pressures were wild again. I started cooling it with a hose again and the pressures dropped, but they are just high enough to keep the clutch engaged. Forgive me as I don't remember the exact numbers. I do know that Brian said the low side pegged when the truck first started.



I think my screw up in between the last fill and bringing the truck to work caused a pressure spike, and caused the system to purge. I'm going to get it checked again to to see if this is the case.



I'm up in the air. I was confident this afternoon that cleaning the condensor was the solution. IT has the appropriate 1. 85lbs and was functional as long as the condensor was cool. Now, for the moment, i'm back where I was. Going to get some sleep.

 

[Hoefler]

Does the engine fan come on?? If not, the high pressure switch may be defective. If the compressor stays on with excessively high pressure as well, I would look into the high side switch.

 

[biggy238]

No, the fan didn't come on during this. Steve told me to check it, but I didn't have to opporitunity to. Whats the proceedure for checking the fan? I've only heard it run very few times while i've owned the truck. So few in fact, that it came on a week or two ago and it scared my wife because she didn't know what it was. Even my 96 won't kick on often though. I don't know when it SHOULD operate if it were functioning properly.



What pressure should the high side switch kick out at?

 

[RVTRKN]

And with due respect, I personally will not be putting R22 into anything. Nitrogen, Yes.

It will not hurt your system if you don't run the compressor, the reason for virgin R22 is that when you evacuate the system there will be no trace of it, virgin R22 has no oil in it therefore no trace. Due to the chemical make up of R22, it makes it much easier to detect than R134a, so a small leak in the evaporator can be detected when 134a will not. Everybody has there methods, but you shouldn't eliminate a good trouble shooting tool/method, that can prove there is a leak without pulling your dash apart only to find it leak free.



It seems that you have competent people working with you, so I will limit my advise, but with what you have posted so far, you have a restriction in your refrigerant control. (orifice) I don't know where the filter/screen is located but you need to inspect it to eliminate it as a possibility. Had that happen on my GMC work van, went through everything your going through only to ruin the compressor because the company owner didn't want to pay. (the next paragraph will explain)



Automotive AC is a lot different than the HVAC world, and it should be left to an automotive AC tech to trouble shoot. I work on my own because it is mine and if a friend asks me I tend to say no. I have seen HVAC techs try to fix other people's auto AC's, only to have them spend hours and money on it, and have an auto AC shop fix it anyway. I'm not shy about it and freely admit that I'm not qualified to work on an Auto AC, I am however, more than qualified to work in the HVAC industry.



FWIW, again, R22 will not hurt your system if you don't run the compressor and its virgin R22. Also, if there is a restriction, you are not getting any oil through as well, your compressor does not have an oil sump to lubricate it independantly and it will ruin it if you continue to run it in that condition, that is what the auto tech pointed out as the cause of compressor failure. My boss learned a good lesson on that one, cost him $1200. 00 and a red face, when the Auto tech stated he needs to advertise the fact that even AC techs come to him for repair.

 

[biggy238]

Yes Sir, I understood that you meant for it to be used for troubleshooting only. My reasoning is more from a time constraint perspective, lack of a source, and time to set up and recover R22. That's all. I remember being trained that R22 is easier to determine a leak with. I have a whole list of symptoms right now that aren't adding up.



The last trick was after I cleaned the condensor, with a full charge, the high side and low side both read 150psi, which was up from the 90psi it was on at rest. The lines in and out of the evaporator both frosted (not just sweating)



High Side #ad


Low Side#ad


Low Side Pressure Port#ad


Liquid Line into Evap. #ad

 

[biggy238]

This was on a full 1. 85lb charge. Before I started the system, the ambient air temp was 82* and the pressure was about 90psi. If I remember the chart correctly, this is what it should have read.

 

[RVTRKN]

If your suction line is frosting, the low side is going lower than 150 PSI. Why you are reading 150 PSI, I can't explain it. Pressure temperature relationship tells me that, and that should be your clue. Is it frosted at or before the low side port, the point where the ice starts to form is the location of the restriction, If the restriction is after the port (where ice/frost begins) then that is the reason your low side is showing 150 PSI. Have you inspected the refrigerant control (orifice) filter/screen?