HELP ! A/C Still Not Cold at Idle

[frafreg]

I have not fixed this problem yet. I bought the Haynes Automotive Heating and Air conditioning Manual because I wanted to learn exactly how an a/c system works. I went through the tests and flow charts in the book and came to the conclusion that the compressor from the bone yard must be weak. It's hard to figure out what the exact amount of R134a is needed since this was a converted from an R12 system. According to the guage, the low side is good but the high side is low. When the low side pressure is at about 35 psi, the high side is at about 120 psi. No good! I also went out and bought a 2.5 cfm vacuum pump from Harbor Freight Tools and made sure the system was evacuated properly. I left the pump on for a full hour, then turned it off and checked to make sure there were no leaks by waiting for an additional 15 minutes more. The held a vacuum at - 29 inches. I was pretty sure there was no leak anyway but I wanted to be sure.
One thing I still have not found is that DAMN drain tube where the condensation comes out. I was underneath the car for a half hour looking for the tube and couldn't find it. I never see any condensation coming out of the bottom of the car. I know it is supposed to be located just below the accumulator on the firewall but it must be hidden behind something. I would love to blow that tube out.
I can't afford to replace the compressor. It's a model 10P15C and it would cost me about $350 for a new one. Plus, about $80 for a new accumulator, and however much it costs to put back the R134a. Unfortunately, I have to draw the line at going any further because I don't have any more money to throw at it. The air gets cold after it gets to about 1500 rpm. I guess I'll have to learn to live with it until this junk yard compressor dies. Thanks for your response. I appreciate it.

[kevinande]

The R134 refrigerant requires a larger condenser to be as efficient as R12 was. If your compressor was going to kill the system, it would have done so by now. If it cools "better" at higher rpm's or highway speeds, you may check into getting a fan capable of moving more airflow over the condenser. This will help keep the air cool at idle.

[frafreg]

First, thank you for responding. I appreciate it. I agree with you about the condenser and the efficiency of R12 compared to R134A. The car actually runs cool with the a/c on. The condener fan is working good and there is plenty of air flow through the condenser. I flushed out the condenser and the radiator with the garden hose through the back, and the front to be sure there was adequate air flow.
One thing I have noticed that I think is strange is that I don't have to turn on the blower fan inside the car to get a/c. I can just push the a/c button without turning on the fan, and the compresser turns on. As long as I am moving and I have the vent open, I get cool air through the vents without the fan being on. If you stop at a traffic light, the compresser stays on, but no air moves through the vent. The only time that would be useful would be on the highway. In the city, it doesn't make sense. That can't be right. Can it?
Also, do you think the low pressure switch could have anything to do with it? I read somewhere that I should adjust the screw inside the switch back a quarter turn after converting to R134A because the pressures are different with R134A and R12. I tried that, but it didnt make any difference. It's supposed to change the pressure point at which the compressor cycles on and off. Could the low pressure switch is bad? My compresser never turns off. According to the Haynes Heating and Air Conditioning manual, that is correct. Some systems are designed not to cycle. I realize I'm grasping at straws now but only that is only because I have nothing left to scrutinize. This really bugs me. I'm out of cash and all I can do is make an educated guess at this point. Thanks.

[kevinande]

Well let me see if I can cover all your questions. 1st the low pressure switch is just what it sounds like. If there is no or low pressure in the system, the switch either disables or cycles the clutch to keep from damaging the system. So if the system is working, more than likely the switch is functioning properly.

I have a ZX2 as a daily driver, and although there are some differences there are some basics that are the same. My car engages the compressor in every mode on the dial, even what is considered "vent" mode. the only thing you can do is turn up the temp gauge if it is uncomfortable to you. I know for a fact that most modern vehicles are designed to operate the compressor in defrost mode to remove moisture from the air, but this is the first car I have ever seen do it in vent mode. Additionally, the only way the system is actually off, is when the mode selector is in the off position. Any other position turns the system on. Remember, there is no off on the fan speed. The best you can do is put it in the lowest position. So even when you think it is off, it is actually running. (That is of course if your setup is like mine.)

I know it is hot as the dickens this summer, but if you have it working enough to keep you comfortable, I would just go with it. The car is 20 years old and you don't have lots of cash to put into it. Might be cheaper to get another car? Sounds as if you have done everything properly, aside from replacing with all new components that is about all you can do. Be careful with that vacuum pump as well. It is easy enough to collapse those lines if you pull too much vacuum.

[frafreg]

Thanks for your reply. I will have to just learn to live with it. It bugs me that I did everything by the book as usual yet, I got poor results. I have taken compressors from the junk yard a few times before and never had this results. They aslways performed good. This is the first time I got a weak one. There isn't anything else to check. The a/c system is prett stright forward. The only thing I haven't checked is the a/c module. I'm not even sure where it is locted or if it has anything to do with my problem. Other than that, I'm outta tricks and money. Thanks for your help. I appreciate it.

Originally Posted by kevinande

Well let me see if I can cover all your questions. 1st the low pressure switch is just what it sounds like. If there is no or low pressure in the system, the switch either disables or cycles the clutch to keep from damaging the system. So if the system is working, more than likely the switch is functioning properly.

I have a ZX2 as a daily driver, and although there are some differences there are some basics that are the same. My car engages the compressor in every mode on the dial, even what is considered "vent" mode. the only thing you can do is turn up the temp gauge if it is uncomfortable to you. I know for a fact that most modern vehicles are designed to operate the compressor in defrost mode to remove moisture from the air, but this is the first car I have ever seen do it in vent mode. Additionally, the only way the system is actually off, is when the mode selector is in the off position. Any other position turns the system on. Remember, there is no off on the fan speed. The best you can do is put it in the lowest position. So even when you think it is off, it is actually running. (That is of course if your setup is like mine.)

I know it is hot as the dickens this summer, but if you have it working enough to keep you comfortable, I would just go with it. The car is 20 years old and you don't have lots of cash to put into it. Might be cheaper to get another car? Sounds as if you have done everything properly, aside from replacing with all new components that is about all you can do. Be careful with that vacuum pump as well. It is easy enough to collapse those lines if you pull too much vacuum.

[danielsatur]

Try running the air cond with recycled air inside of car instead of hot fresh air that needs tobe cool.

[frafreg]

UPDATE! I just couldn't let this go. I went outside yesterday, and I took some more readings. The Haynes Automotive Heating and Air Conditioning Techbook has a test for the low pressure switch on the FFOT or Ford Fixed Orifice Tube system. I didn't think this was my problem but I tried the test anyway. I turned on the a/c without the blower fan, and brought the engine up to 1500 rpm while watching the low pressure guage until it went down between 21 psi and 26 psi, to see if the compressor cycled off. It didn't. I NEVER see the compressor cycle off unless it doesn't have enough R134A. The inlet hose to the evaporator got very cold. There is a screw beneath the plug on the low pressure switch that is adjustable. I backed it off a quarter turn to see if it made any difference in the cycling of the compressor but it did not. I put the screw back to it's original position. All that information is not so important as what happened next. I left the blower fan off for another few minutes until the low pressure side went up to about 100 psi. The high side pressure was at about 250 psi. Then, I turned the blower fan back on high to bring the low pressure side back down. It would NOT come back down into the normal range. It went down about 30 psi but would not go down into the normal range no matter how fast I raised the rpm. At that point, I thought I needed to wait longer before continuing testing, and left the car alone for a few hours. I closed up everything, and went inside. A few hours later, I got in the car, turned on the a/c, and I got cold air again. Now, I'm beginning to think I have a blockage.
I have never seen this type behavior before in all of the testing I have done. I may have a bad low pressure switch but something else is wrong if the low pressure side will not go back to normal unless I turn off the system and wait such a long period of time. Any thoughts are welcome at this point.

Originally Posted by danielsatur

Try running the air cond with recycled air inside of car instead of hot fresh air that needs tobe cool.

[frafreg]

I just called Advanced Auto Parts for a replacement switch. There are two different switches, one for R12 and one for R134a. I never replaced the switch when I converted from R12 to R134a because I was never told that is was necessary. The new accumulator didn't come with a switch, so I just used the original switch that came with the car back in 1990 when the system was using R12. I am picking up the new switch recommended fro R134a from Advanced Auto Parts tonight. I hope this works. It sure as hell can't hurt. Thanks.

Originally Posted by kevinande

Well let me see if I can cover all your questions. 1st the low pressure switch is just what it sounds like. If there is no or low pressure in the system, the switch either disables or cycles the clutch to keep from damaging the system. So if the system is working, more than likely the switch is functioning properly.

I have a ZX2 as a daily driver, and although there are some differences there are some basics that are the same. My car engages the compressor in every mode on the dial, even what is considered "vent" mode. the only thing you can do is turn up the temp gauge if it is uncomfortable to you. I know for a fact that most modern vehicles are designed to operate the compressor in defrost mode to remove moisture from the air, but this is the first car I have ever seen do it in vent mode. Additionally, the only way the system is actually off, is when the mode selector is in the off position. Any other position turns the system on. Remember, there is no off on the fan speed. The best you can do is put it in the lowest position. So even when you think it is off, it is actually running. (That is of course if your setup is like mine.)

I know it is hot as the dickens this summer, but if you have it working enough to keep you comfortable, I would just go with it. The car is 20 years old and you don't have lots of cash to put into it. Might be cheaper to get another car? Sounds as if you have done everything properly, aside from replacing with all new components that is about all you can do. Be careful with that vacuum pump as well. It is easy enough to collapse those lines if you pull too much vacuum.

[zzyzzx2]

I am not sure that I would want to use a junkyard compressor, specifically for the reasons cited by denisond3

[frafreg]

You're right. I didn't want to use a junk yard compressor but I was strapped for cash. The cost of the repair would have been an extra $350 which didn't have at the time. As a matter of fact, I still don't have that much money to sink into this project. I noticed when testing yesterday that the pressure switch is not workin gcorrectly. I am going to pick that up tonight and replace it hopefully, tomorrow some time. It costs another $17.89 plus tax. The original switch that looks bad, is the one that came with the car back in 1990, when it still ran on R12. This new switch is designed to work with R134a. I think if the old switch was good, it would have been good enough but since it is bad, I might as well go ahead and replace it with the correct one. Since the compressor never cycled, maybe, that could have been the problem. I hope so.

Originally Posted by zzyzzx2

I am not sure that I would want to use a junkyard compressor, specifically for the reasons cited by denisond3

[frafreg]

I picked up and installed my new R134a pressure switch which mounts on the accumulator last night. I still haven't had a chance to put the guages on the system to see if the compressor is cycling at the correct points yet. According to the Haynes manual, it is supposed to cycle off between 21 and 28 psi. The original switch which was designed for R12, never cycled the compressor. I'll have to wait and try it on a hot sunny day also to see if it maintains any level of cold air while at idle. Interestingly enough, all of the test are made at 1500 rpm, not at idle. Just the same, at 1500 rpm, the air didn't seem cold enough. We'll see.

Originally Posted by kevinande

Well let me see if I can cover all your questions. 1st the low pressure switch is just what it sounds like. If there is no or low pressure in the system, the switch either disables or cycles the clutch to keep from damaging the system. So if the system is working, more than likely the switch is functioning properly.

I have a ZX2 as a daily driver, and although there are some differences there are some basics that are the same. My car engages the compressor in every mode on the dial, even what is considered "vent" mode. the only thing you can do is turn up the temp gauge if it is uncomfortable to you. I know for a fact that most modern vehicles are designed to operate the compressor in defrost mode to remove moisture from the air, but this is the first car I have ever seen do it in vent mode. Additionally, the only way the system is actually off, is when the mode selector is in the off position. Any other position turns the system on. Remember, there is no off on the fan speed. The best you can do is put it in the lowest position. So even when you think it is off, it is actually running. (That is of course if your setup is like mine.)

I know it is hot as the dickens this summer, but if you have it working enough to keep you comfortable, I would just go with it. The car is 20 years old and you don't have lots of cash to put into it. Might be cheaper to get another car? Sounds as if you have done everything properly, aside from replacing with all new components that is about all you can do. Be careful with that vacuum pump as well. It is easy enough to collapse those lines if you pull too much vacuum.