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2004 Frontier Crew Cab 4WD
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Discussion Starter #1 (Edited)
With the engine off and pressure equalized between high side and low side, they both show about 115PSI. With the engine running and AC on max, they hover around 30 and 95 PSI, respectively.

I hold the engine at 1500RPM, and with the fan on low, or doesn't get below 48° F. With the fan on high, it's ~64°.

Some things I've read say high side pressure should be roughly double the low side, plus fifty, which would mean at 30 on the low side, high would be ~110. Other sources say 30 - 45 low side and high side 190 - 230.

The low side seems pretty normal, but why is my high side pressure actually dropping when it puke refrigerant from the low side? Shouldn't it go up? I'm confused.

Is this inductive of a problem? If so, what? Also! Before you ask, I tested my gauges against other known working, accurate gauges, and they are right on the money. So that's not the problem.

Almost forgot: ambient temperature is right about 90° F here.

Ideas?
 

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1. You're low on refrigerant because you have a leak.
2. You need to find the leak and repair it, then evacuate and recharge by weight.
3. If you just add refrigerant, might work for a few days.
4. If you add refrigerant that contains a sealer or sealing agent, you may ruin the entire system PERMANANTLY. Shops also won't even attempt to work on systems containing sealer (they test).
 

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Discussion Starter #3
Does anyone else want to address the actual questions/issues I'm having? Why would the high side drop when the compressor is running and then go back up when it shuts off? Shouldn't it only go up when the compressor is running, due to refrigerant moving from the low side to the high side? Why would the low side pressure be right where it should be while the high side is reading significantly lower than it should? If it's able to cool to 48° F with the fan on low but not be able to maintain that with the fan on high, it would seem like it is working, just not very efficiently, and it could maybe use more refrigerant. However, I obviously don't want to overcharge it.

I don't have the equipment or money to reclaim the refrigerant, and I don't want to release it into the atmosphere. I already vacuum tested it last year after buying it with zero refrigerant in the system. I replaced the receiver dryer and a majorly-leaky hose, good as new. I charged it by weight, and it was working fine. In fact, it still works fine, as long as it's not friggin 90° outside.

What I want to know is not if stop-leak is bad or if ACs are charged by weight or volume. What I want to know if what I asked about: the pressures. If I know what the pressures should be or are on other working vehicles, or if someone is familiar with these symptoms, it would help me understand what might be going on. Vaccing down and recharging by weight would not fix whatever is going on with it.
 

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Most places offer an A/C system check for less than 100 dollars.
 

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Pressures give an indication. The proper amount of refrigerant by weight is correct and best way.

Just because you don't have such equipment to weigh the refrigerant doesn't mean you should "wing it".

Keep in mind: you're having trouble attaching an engine skid plate (a different post), so maybe AC is too much for you !!!
 

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Discussion Starter #6
Cusser, please do me a favor and don't bother replying to my posts anymore. It seems you're much more interested in proving me wrong than you are in helping. (That's the politest version possible of the reply you deserve.)

Invasion, I know what services are available, but if I can get an answer that makes me more knowledgeable and potentially helps others down the road with similar questions, and for free, that's the route I'm going to take. It's a good plan A, either way. Failing that, I will spend the money, but I'll avoid it if I can. Trying to hold onto what little I have in the middle of a pandemic. You can tell how much money I (don't) have by the fact that I drive a 16-year-old used truck with 180k+ miles on it and constant issues. It's not a hobby. It's a necessity.

And I can figure these things out on my own, but again, that's plan B. If someone is able to tell me how to do something based on their personal experience, it can save me a lot of time and trial and error.

I find it kind of hard to believe that no one is able to simply tell me what pressures their healthy AC is running. It's not a big ask. I thought this forum was to share experiences and help each other, not to tell people to throw money at their problems and lecture and belittle them.
 

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Cusser, please do me a favor and don't bother replying to my posts anymore. It seems you're much more interested in proving me wrong than you are in helping. (That's the politest version possible of the reply you deserve.) I thought this forum was to share experiences and help each other, not to tell people to throw money at their problems and lecture and belittle them.
This will be my last response to you. No - I am NOT here trying to prove you wrong; I learned long ago not to have a battle of wits with an un-armed person. I was trying to help you understand that you should focus on the total oz. R134a rather than the pressures; pressures are just an indicator, and your goal is to get proper cooling, NOT to read best pressures.


I find it kind of hard to believe that no one is able to simply tell me what pressures their healthy AC is running. It's not a big ask.
For the record, I have both a 1998 and a 2004 Frontier in Arizona desert and the pressures - when it's hot outside, that's when I use my AC - are about 35 psi on low and about 250 psi on high side, all measured at about 1800 rpm as they should. And the AC in both my Frontiers cool EXTREMELY well.

Yes, vent temperatures will be colder at LOW blower fan speeds, as the hot air has more time to shed its heat to the evaporator coils.

My 1998 has 250K miles and has needed the high pressure hose replaced and an AC clutch shim removed last summer due to intermittent slippage. My 2004 had its compressor seize at 103K and I replaced the compressor, condenser, and drier. Yes, I did all those repairs myself.


Some things I've read say high side pressure should be roughly double the low side, plus fifty, which would mean at 30 on the low side, high would be ~110.
That's just WRONG. My guess is they meant 2 x ambient temperature in Fahrenheit plus 50, or you read it wrong.
 

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Discussion Starter #8 (Edited)
Thank goodness that's over with.

Does anyone know what the pressure should be (ballpark) in 90° weather with the engine off, or why the high side pressure would drop when the compressor is running? Seems like it would pull volume from the low side to the high side, and pressure would decrease on the low side and increase on the high side. But both drop. Is that normal? If not, what could be the cause?
 

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Does this help?
 

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Discussion Starter #10
Looks very promising. I'll look at it more tomorrow in the light of day. But thank you anyway.
 

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2004 Nissan Frontier XE KC KA24DE
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For the record...the FSM is available to all, free of charge.
Screenshot_2020-07-23-11-05-20-1.png
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Post #2 should've been the last post in this thread because it's 100% accurate and is solid advice....IMO.
Your "Plan B" is always my "Plan A".
 
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