A/C question/trouble shooting help

Case Nutty 1660

Well-known Member
Guy's, I have done a/c work for many years but have never had any "training" so to speak. The issue I am having is on a aftermarket system, all at once it quit cooling, the compressor runs, the cooling fans and blower fans work fine, it holds a charge on freon but will not cool at all, I tried discharging the system and recharging still the same, I will hook my gauges back up and get readings for you, will a plugged receiver drier cause this or does it sound like a expansion valve issue or am I totally off base? thanks for any ideas, I had thought I had a compressor issue but it seems to recharge/pump fine it just does not cool, if I remember right it seemed to have a little lower low side pressure than before when it was working but I may be thinking of another system, let me know if I need to test some thing else to give more info thanks again,
ps this has a "York" style compressor not a rotary
cnt tom
 
My experience is in automotive a/c, and it's mighty limited. BUT...if the system's not leaking your refrigerant...and the compressor gets the system up to correct pressure...but it still won't cool...

Well, there's a low pressure switch that tells the compressor when to kick on, and a high pressure switch that tells it when to kick off. From that point, you're not getting your refrigerant to circulate if it's not cooling.

In the automotive side, you'll either have an expansion valve or an orifice tube. The orifice tubes generally have a screen attached...and they do get blocked. So that's where I'd start first, on a car with those symptoms. Then, if the screen and/or the orifice tube are blocked...the next question would be, what's getting in there to block the system? Is something in the system breaking down, something that might immediately block a new orifice?

Once you get there, you'll have your answer. But as I said, my experience is VERY limited. The idea that the "low" side pressure is lower than before has me leaning to the blocked orifice or expansion valve. But I might be wrong; I'm married, so being wrong is my normal position.
 
I would think that a broken compressor shaft wouldn't allow the compressor to build any pressure...but as in my other post, I've been wrong before, so I'm used to that.
 
My MF-690 was the same way. Checked and re-checked everything, tested the low pressure switch and the high pressure switch, nothing would help. Expansion Valve fixed it. Tom
 
Given the symptoms as I understand them, it's not cooling but it's charged correctly, the low side is probably lower than it should be, and the high side is otherwise reading within an acceptable range, it sounds to me like the expansion valve isn't working properly. Basically, if it doesn't open far enough it will cause the low side to be lower than normal because the compressor is trying to suck the refrigerant through it, but can't. On the high side there is no where for the gas that is being pumped to go, so oftentimes the high side pressure can be higher than normal, but still show within an acceptable range given the allowable variations due to outside temp, humidity, etc.

That said, I've been working on equipment A/C systems for about 15 years now, both the OEM and aftermarket ones. Unless they have come out with something new every one of them I have seen runs an expansion valve instead of an orifice tube. So, if I saw what you are describing on a customers machine the first thing I would do is replace the expansion valve, and more than likely go ahead and replace the receiver/dryer also for added insurance.
 
Guy's, Thank You very much for the reply's, I should have added that yes , the compressor runs and does not cycle like this type of system does when working properly, the lines both get Hot, the compressor seems fine to me as when you have the gauges hooked to it I can add Freon no problem but even fully at max charge/PSI on the high side no cooling at all, I will get a new receiver drier and expansion valve and put in.

thank you again
cnt
 
(quoted from post at 16:07:31 07/28/14) Guy's, I have done a/c work for many years but have never had any "training" so to speak. The issue I am having is on a aftermarket system, all at once it quit cooling, the compressor runs, the cooling fans and blower fans work fine, it holds a charge on freon but will not cool at all, I tried discharging the system and recharging still the same, I will hook my gauges back up and get readings for you, will a plugged receiver drier cause this or does it sound like a expansion valve issue or am I totally off base? thanks for any ideas, I had thought I had a compressor issue but it seems to recharge/pump fine it just does not cool, if I remember right it seemed to have a little lower low side pressure than before when it was working but I may be thinking of another system, let me know if I need to test some thing else to give more info thanks again,
ps this has a "York" style compressor not a rotary
cnt tom

As previously stated . Plugged expansion valve orifice or dryer receiver plugged .
 
Not worth the trouble, if it has an orifice tube. They're pretty cheap. And if it has an expansion valve, those don't come apart to clean. You need to find out which this system has.

And an R-134 orifice tube is a different size from an R-12 orifice tube.
 
good or high head pressure and low suction pressure txv is a good start. only way to know if you got right freon is re-cover and re-weigh goin back in.
 
The type of compressor is irrelevant. They all perform the same function - moving the refrigerant.
Gauge readings are important. High side as well as low side. Under average conditions on a rather warm day, and depending on the refrigerant used, the high side should run about 250 to 350 with R-134a. Low side should run between 25 and 45. Note that these are APPROXIMATE numbers. Under or over charge will affect them. Ambient temperature will also affect them. Now, having said all of that, if your gauge readings seem to be in the right range, it would point to an expansion valve. Most non-cycling systems use an expansion valve rather than a fixed (or variable) orifice. Some cycling systems also use an expansion valve. It is up to you to determine which you have.
Now, the things that will affect cooling capacity of the unit:
1) Over or under charge. Be sure that you have the right amount of refrigerant in the system.
2) Air in the system. Air is a non-condensable gas. This means that it will NOT change state from gas to liquid and back to gas within the operating parameters of a refrigeration system designed for R-134a or R-12.
3) Too much OIL in the system. The opposite of air, but with the same effect. Too much oil will displace the refrigerant, and will prevent the proper changing of state of the refrigerant from liquid to gas and back to liquid.

Surprisingly, these systems are very simple yet difficult for many to understand. The basic principle of refrigeration is that a liquid refrigerant is sprayed through a metering device into a coil called an evaporator. The change of state from a liquid to a gas absorbs a tremendous amount of HEAT from the interior of what you are cooling. The entire system is designed to provide that liquid to the evaporator for cooling to take place. This means that after the liquid has evaporated, it needs to be returned to a liquid again for continued cooling. The system is designed to do that in a closed environment. In your case, this is not happening. The causes I have listed are the major causes of a no cooling problem.
Good luck, and I hope this is of some help.
 
A plugged or otherwise restricted expansion valve or orifice will cause both high and low side pressures to be low. What happens is all of the refrigerant ends up in the condenser. With little or no refrigerant coming through to the suction side of the compressor, the compressor has little or nothing to pump. Little or nothing to pump equals little to no heat from the discharge side. No heat on the discharge side equals low pressure. Orifice tubes are not refrigerant specific, they are color coded for flow rates only.
 
again thank you for the reply's, I was pretty sure I had a restriction, I have charged and worked on these systems since 1968, and know how to charge, change components ect, I have seen two systems do what this one did, first one was in my pickup years ago, paid a certified a/c tech to check out my problem he assured me it was a bad, I changed it no change at all, it had never worked since I had bought it, this system I am trying to fix now worked very well for years one day during harvest in the afternoon it just quit cooling, did not lose it charge it just quit cooling like you threw a switch, in the past 46 years I have charged hundreds of systems changed hoses, compressors ect never had a problem except with these two, I will start with the receiver dryer, then the expansion valve with be next if that does not fix the issue, I just hate throwing parts at something, I wanted to be sure what was wrong, I guess I know something as this was what I was going to change before posting my questions, I will post back on the results thanks again
cnt
 
If the expansion valve is restricted but not completely closed off there will usually be frost forming on it. That applies to a restriction anywhere in the system. As long as there is some circulation there will be a temperature change where ever there is a restriction causing pressure change.
 
Gotta disagree!! A plugged system will cause the high side to go too high and the low side to go too low. Can't happen any other way.
Why?
Because a blockage will cause the compressor to deadhead. Low side can even go into vacuum. But the refrigerant you say is "trapped in the condenser" is STILL UNDER PRESSURE! The only way for the high and low side to BOTH go too low is a loss of refrigerant. Period.
 
If the system has enough capacity to hold the liquid refrigerant between the compressor and the restriction it is quite possible for the high side pressure not to go high but instead to remain low.

Shortly after the IH 86 series tractors came out they had a problem with a screen in the expansion valve becoming plugged. When that happened if you installed the gauges and turned on the AC the high side pressure would go up a little and then drop back down while the low side would drop into a vacuum. All the refrigerant would end up in the condenser, the receiver dryer tank, and high pressure lines. Since there was no circulation the refrigerant did not pick up any heat so the fan pulling air through the condenser kept it at ambient temperature.
 

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