The drier and both lines to it are at ambient temp, maybe just slightly higher. Ambient now is about 85F and the "cold" air is 60F. The low pressure remains at 30 psi, but the high is now more like 375F (again, all at 2000 rpm).
I will keep trying anything you can suggest as soon as possible, trying to get a handle on this before the charge leaks too low.
'94 Saturn A/C, need opinions
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billr
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Re: '94 Saturn A/C, need opinions
Am I focused in the wrong direction, blaming the TXV for the abnormally high "high" pressure? Is this a variable-displacement compressor that could be failed in the "full stroke" position and not modulating the flow?
Re: '94 Saturn A/C, need opinions
I am hearing elsewhere that it is a variable-displacement compressor. New info:
I ran new tests today (full data below). At my TXV the top line is larger and colder (39F) than the bottom line (93F).
Which begs a new question: How does that fluid go through the evaporator and come out at 39F, yet the air that flows across the evaporator only makes it down to 52F? That seems like a pretty poor heat exchanger. Is the heater core always flowing hot coolant, could this poor performance be a "blend door" issue? I never hear of a condensate drain on these cars; is there none? No way I can put a probe up near the evaporator?
I have a more reliable way to read temps now. As a sanity-check, I filled an aluminum cup with ice-water and measured in the water and the outer surface of the cup. In the water, stirring rapidly, it read 32.2F, on the outer surface 40F (but not enough hands to stir while doing that). So, I now have some confidence that the fluid is expanding and cooling fairly well.
Here are latest readings:
Ambient temp = 78F sitting overnight in close garage, before engine started
Static pressure = 80 psi (same conditions as above)
Humidity = 35%
Low-side = 30 psi (engine at 2000, long enough for reading to stabilize)
High-side = 375 psi "
Cold air = 52F "
TXV port temps = 93/39F "
Compressor port temps = 39/156F "
I have no clue if/when the compressor was at min or max stroke? Is there any way to tell, or force it to one extreme or the other?
I ran new tests today (full data below). At my TXV the top line is larger and colder (39F) than the bottom line (93F).
Which begs a new question: How does that fluid go through the evaporator and come out at 39F, yet the air that flows across the evaporator only makes it down to 52F? That seems like a pretty poor heat exchanger. Is the heater core always flowing hot coolant, could this poor performance be a "blend door" issue? I never hear of a condensate drain on these cars; is there none? No way I can put a probe up near the evaporator?
I have a more reliable way to read temps now. As a sanity-check, I filled an aluminum cup with ice-water and measured in the water and the outer surface of the cup. In the water, stirring rapidly, it read 32.2F, on the outer surface 40F (but not enough hands to stir while doing that). So, I now have some confidence that the fluid is expanding and cooling fairly well.
Here are latest readings:
Ambient temp = 78F sitting overnight in close garage, before engine started
Static pressure = 80 psi (same conditions as above)
Humidity = 35%
Low-side = 30 psi (engine at 2000, long enough for reading to stabilize)
High-side = 375 psi "
Cold air = 52F "
TXV port temps = 93/39F "
Compressor port temps = 39/156F "
I have no clue if/when the compressor was at min or max stroke? Is there any way to tell, or force it to one extreme or the other?
Re: '94 Saturn A/C, need opinions
I'm going to post this in a couple of other forums, so a quick recap:
High-side pressure is too high (300+psi), low-side OK
Condenser seems to be working OK, fluid lines cool from about 150F at compressor discharge to near-ambient at drier. Also, I misted the condenser with 70% isopropyl alcohol and it had no effect on the high-side pressure. Yeah, I have gallons of that alcohol, I used plenty! Engine fan is working.
Temps in and out of the drier are the same (the near-ambient), and no cold spots on the drier. I don't think there is restriction in there.
By blocking flow of hot coolant to the heater core, I can get 32F at the TXV outlet. Again, with "near-ambient" (85-95F) going into TXV. It would seem the TXV is doing all that I could expect. And, cool air from the dash vent was 42F.
So, time to take it on the road, right? That quickly was a bummer! The cooling stopped in just a few minutes, and the engine had a stumble right from the beginning; being bogged down by load from the compressor.
OK, I've pouted overnight and licked my wounds, now it is time to regroup. I'm now thinking that variable-displacement compressor is getting "stuck" at full stroke. Does anybody have info on how that compressor works? Any cut-away diagram of its mechanisms? Is there any way to determine what the stroke position is at any given time, or be able to force it to a particular position? I hate to just throw a compressor (and drier too, of course) at it.
High-side pressure is too high (300+psi), low-side OK
Condenser seems to be working OK, fluid lines cool from about 150F at compressor discharge to near-ambient at drier. Also, I misted the condenser with 70% isopropyl alcohol and it had no effect on the high-side pressure. Yeah, I have gallons of that alcohol, I used plenty! Engine fan is working.
Temps in and out of the drier are the same (the near-ambient), and no cold spots on the drier. I don't think there is restriction in there.
By blocking flow of hot coolant to the heater core, I can get 32F at the TXV outlet. Again, with "near-ambient" (85-95F) going into TXV. It would seem the TXV is doing all that I could expect. And, cool air from the dash vent was 42F.
So, time to take it on the road, right? That quickly was a bummer! The cooling stopped in just a few minutes, and the engine had a stumble right from the beginning; being bogged down by load from the compressor.
OK, I've pouted overnight and licked my wounds, now it is time to regroup. I'm now thinking that variable-displacement compressor is getting "stuck" at full stroke. Does anybody have info on how that compressor works? Any cut-away diagram of its mechanisms? Is there any way to determine what the stroke position is at any given time, or be able to force it to a particular position? I hate to just throw a compressor (and drier too, of course) at it.
Re: '94 Saturn A/C, need opinions
The compressor in that car has an internal control valve, but it is not really variable displacement.
The compressor is a vane pump. The output is always the same, the valve throttles to maintain a suction side slightly above freezing - 30 psi or so.
Scroll down to page 53 for an exploded view of your compressor:
http://www.omega-usa.com/client/images/ ... ent%20.pdf
If the valve was stuck it should go in to vacuum on the low side, or pump almost nothing, depending on where it was stuck.
I suspect a restriction someplace between the compressor discharge and the receiver, or perhaps way too much oil. The high side pressure does not mesh with the discharge temperature.
If the TXV was plugged up the suction line would not be cold, and the high side would be low as the refrigerant would be liquid in the receiver.
I don't know what planet you live on, burt here on earth water is abundant, and usually used for testing condenser performance. Apparently where you are there is plenty of 70% alcohol to spray on a hot engine. Hope you have some water to put it out with...
The compressor is a vane pump. The output is always the same, the valve throttles to maintain a suction side slightly above freezing - 30 psi or so.
Scroll down to page 53 for an exploded view of your compressor:
http://www.omega-usa.com/client/images/ ... ent%20.pdf
If the valve was stuck it should go in to vacuum on the low side, or pump almost nothing, depending on where it was stuck.
I suspect a restriction someplace between the compressor discharge and the receiver, or perhaps way too much oil. The high side pressure does not mesh with the discharge temperature.
If the TXV was plugged up the suction line would not be cold, and the high side would be low as the refrigerant would be liquid in the receiver.
I don't know what planet you live on, burt here on earth water is abundant, and usually used for testing condenser performance. Apparently where you are there is plenty of 70% alcohol to spray on a hot engine. Hope you have some water to put it out with...
Re: '94 Saturn A/C, need opinions
Yes, I understand now that it is fixed-displacement with a cam-plate /port-plate to throttle the intake. I can only wonder how that extra expansion of the fluid through that throttle affects the theoretical thermodynamic cycle.
Somebody pointed out that big adjusting screw on the suction end of the compressor and suggested turning it a bit. Any opinion on that? Is that screw a mechanical stop for the throttle?
I gotta ask... have you ever tried to light that rubbing alcohol? There is nothing hot enough on a lightly-loaded engine to do so, even if there was an exhaust leak right at the manifold. I used the alcohol both because it was handy (I have many gallons looking for a use) and I feel it does evaporative cooling better than water; I wanted to have the best chance of seeing a difference if the problem was poor operation of the condenser. Do you think the alcohol was not adequate, not as good as water alone?
Somebody pointed out that big adjusting screw on the suction end of the compressor and suggested turning it a bit. Any opinion on that? Is that screw a mechanical stop for the throttle?
I gotta ask... have you ever tried to light that rubbing alcohol? There is nothing hot enough on a lightly-loaded engine to do so, even if there was an exhaust leak right at the manifold. I used the alcohol both because it was handy (I have many gallons looking for a use) and I feel it does evaporative cooling better than water; I wanted to have the best chance of seeing a difference if the problem was poor operation of the condenser. Do you think the alcohol was not adequate, not as good as water alone?
Re: '94 Saturn A/C, need opinions
I think that before I tinkered with the control valve assembly, I would find the cause of the high pressure. The low side seems to indicate the compressor is working.
Ever try to light 200f alcohol vapor? All it takes is a bad plug wire. I know IPA is not Methanol, but I have worked around enough alky burners to be very careful. I once had a bad plug wire light some raw fuel from a bowl vent - that was a surprise.
The thing about water is you can use a lot more of it. When we say mist we are talking about a garden hose - and if you still see high pressures you can drench the condenser to see if anything changes.
I would check the dryer in your car. Is it all the same temperature? Have any cold spots? What about the condenser? Perhaps a hard line someplace that has some road damage? A careful, inch by inch inspection may tell you something.
Ever try to light 200f alcohol vapor? All it takes is a bad plug wire. I know IPA is not Methanol, but I have worked around enough alky burners to be very careful. I once had a bad plug wire light some raw fuel from a bowl vent - that was a surprise.
The thing about water is you can use a lot more of it. When we say mist we are talking about a garden hose - and if you still see high pressures you can drench the condenser to see if anything changes.
I would check the dryer in your car. Is it all the same temperature? Have any cold spots? What about the condenser? Perhaps a hard line someplace that has some road damage? A careful, inch by inch inspection may tell you something.
Re: '94 Saturn A/C, need opinions
OK, I didn't understand that "misting" meant flooding with a garden hose. That will make a nice mess in my garage, but I'll do that if/when I get back to testing. I would rather have the water on the floor than replace a compressor that is actually still good.
You asked before about the dryer and I answered that there are no cold spots and both in/out lines are the same temp, ambient or just a bit higher. Doesn't the fact that the condenser cools the hot high-side discharge down to ambient kind of prove the condenser is working OK?
Regardless, I just went and checked the front surface of the condenser. There is no sign of damage to that front side, or to any of the plastic shrouds, and no sign of a leak using UV. The front face does have bugs and other debris, since it has been there for 24 yrs/220K miles now, but I'm thinking air flow (and the coolant fan) are "good enough" since there the engine cools fine and the condenser even gets the air first chance at the ambient air.
The low-side (and high, for that matter) certainly indicate the compressor is "working" in that it can compress, but it isn't at all clear to me that the throttle in the compressor is working properly. Maybe I am misunderstanding again: are you saying that the high-side should not be going that high even if the compressor throttle was stuck wide-open?
You asked before about the dryer and I answered that there are no cold spots and both in/out lines are the same temp, ambient or just a bit higher. Doesn't the fact that the condenser cools the hot high-side discharge down to ambient kind of prove the condenser is working OK?
Regardless, I just went and checked the front surface of the condenser. There is no sign of damage to that front side, or to any of the plastic shrouds, and no sign of a leak using UV. The front face does have bugs and other debris, since it has been there for 24 yrs/220K miles now, but I'm thinking air flow (and the coolant fan) are "good enough" since there the engine cools fine and the condenser even gets the air first chance at the ambient air.
The low-side (and high, for that matter) certainly indicate the compressor is "working" in that it can compress, but it isn't at all clear to me that the throttle in the compressor is working properly. Maybe I am misunderstanding again: are you saying that the high-side should not be going that high even if the compressor throttle was stuck wide-open?
Re: '94 Saturn A/C, need opinions
If the compressor was running "wide open" it would suck the low side down below 30 psi quickly.
Back the car out of the garage and clean the condenser. Use a strong surfactant like simple green or zep orange. Spray a lot of it deep in to the fins & let it soak for a few minutes. Then flush it out with the garden hose. Repeat. Get the condenser clean.
Then test it with some water spraying on it.
Just because a car does not overheat, that does not mean the condenser is getting enough airflow.
Back the car out of the garage and clean the condenser. Use a strong surfactant like simple green or zep orange. Spray a lot of it deep in to the fins & let it soak for a few minutes. Then flush it out with the garden hose. Repeat. Get the condenser clean.
Then test it with some water spraying on it.
Just because a car does not overheat, that does not mean the condenser is getting enough airflow.
Re: '94 Saturn A/C, need opinions
"Life got in the way of this project", it will be a while before I get back to it. However, I did make some progress just before the halt. The last time I checked, things were like this:
Ambient temp 78F, static pressure 79.5 psi, humidity 35%
Low/high pressures 23/160 psi at 2000 rpm
Low temp at TXV 31F
31F? Pretty good, huh? So I then drove it several times over the next day or two and the dash cooling seemed adequate (heater loop has been restored).
My conclusion is that it was over-charged and had slowly leaked down to the correct range. My suspicion is that the root cause here is this system does not exhibit the normal R134a pressures. Maybe because of that throttling arrangement to simulate variable-displacement?
My point is, looking for R134a pressures will routinely get you charts specifying L = 40-50 psi at 80F (35-45 psi at 70F); so I started charging and the high was way too high by the time the low got to 30 psi. And that wasn't even up in the normal range yet (35-50).
I repeatedly posted that low as being 30 psi, and nobody noted that it was high. However, "fdreyer" (of <satrunfans.com>) did post charts (from the FSM?) that show lower pressure. Specifically, L = 24-30 psi at 80F (29-33 at 70F). So, I had it over-charged, my mistake, but I had help doing so and not recognizing it.
Since it now seems to function OK, i have a new plan:
I'm going to remove the compressor to fix the leaks at its in/out ports and drain the oil. If the oil looks OK, I will reinstall the compressor (with no leaks, I hope!) with the proper amount of new oil for a "compressor R&R alone), then do the whole leak-check/evacuate and charge routine again. I'm going for the oil change both for the chance to examine the old oil and because I have little clue how much is left after all these years of leaking and testing. Yes, I will tightly cap the two lines to the compressor while I have it off to keep the system as clean and moisture-free as possible.
Wish me luck!
PS: how much oil for just the compressor, and what type? It sounds like this vane compressor takes a different viscosity/type than the more common piston compressors.
Ambient temp 78F, static pressure 79.5 psi, humidity 35%
Low/high pressures 23/160 psi at 2000 rpm
Low temp at TXV 31F
31F? Pretty good, huh? So I then drove it several times over the next day or two and the dash cooling seemed adequate (heater loop has been restored).
My conclusion is that it was over-charged and had slowly leaked down to the correct range. My suspicion is that the root cause here is this system does not exhibit the normal R134a pressures. Maybe because of that throttling arrangement to simulate variable-displacement?
My point is, looking for R134a pressures will routinely get you charts specifying L = 40-50 psi at 80F (35-45 psi at 70F); so I started charging and the high was way too high by the time the low got to 30 psi. And that wasn't even up in the normal range yet (35-50).
I repeatedly posted that low as being 30 psi, and nobody noted that it was high. However, "fdreyer" (of <satrunfans.com>) did post charts (from the FSM?) that show lower pressure. Specifically, L = 24-30 psi at 80F (29-33 at 70F). So, I had it over-charged, my mistake, but I had help doing so and not recognizing it.
Since it now seems to function OK, i have a new plan:
I'm going to remove the compressor to fix the leaks at its in/out ports and drain the oil. If the oil looks OK, I will reinstall the compressor (with no leaks, I hope!) with the proper amount of new oil for a "compressor R&R alone), then do the whole leak-check/evacuate and charge routine again. I'm going for the oil change both for the chance to examine the old oil and because I have little clue how much is left after all these years of leaking and testing. Yes, I will tightly cap the two lines to the compressor while I have it off to keep the system as clean and moisture-free as possible.
Wish me luck!
PS: how much oil for just the compressor, and what type? It sounds like this vane compressor takes a different viscosity/type than the more common piston compressors.