A/C not performing well in hot weather after all new parts and recharge

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stamp11127

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AGrayson84

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Hey Stamp, really sorry to hear about the loss of your fur-baby. They're what keep us on our toes sometimes and it's definitely rough when they leave us. Please.... no hurry in responding back to this. I just wanted to post everything up while I had a chance.

So on Saturday morning I did exactly as we had spoken about. There are 4 videos to show you what all is going on. The first video looks really bad at the beginning because my camera lens was full of moisture from all the humidity outside. It clears up and you can see the gauges much better. Here are all 4 videos:




 
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AGrayson84

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My buddy and I did some readings on the rear evaporator later Saturday afternoon. The cabin had already cooled down and the truck was blowing out chilly air when I took the below video. It was a good bit hotter outside an hour before I shot this, but then we had some storm clouds roll in and it went from being a little over 90 degrees outside to around 87 degrees or so (whatever I mentioned as ambient temperature in the video. There was still a bit of overcast at this time, so the sun wasn't very harsh. I kind of wish I had taken these readings while it was over 90 degrees out, while the sun was harsh, and while my cabin was still hot.... but timing didn't pan out.

Something to note is that when measuring the temperatures, we had the thermocouples on the lines right next to the TXV (not the evaporator-side of the TXV) of the rear evaporator. We tried getting readings on lines in the front, but the engine bay was just really increasing the temperatures of the thermocouples so we weren't getting accurate readings, and didn't have any material to try to insulate the thermocouples from the engine heat.

I also kept referring to the numbers you are seeing from the thermocouples as the super heat and sub cooling. Sorry about that. One line was on the liquid line, and the other was on the gas line, if that clears that up. Here is the video:


Not being able to get accurate readings of the suction line closer to the compressor, I'm not sure how good these calculations will be.... but here is what I came up with:

Low side: 25 degrees saturated temperature at @ 24 PSI, rear suction line was 31 degrees. This equals 6 degrees of super heat.
High side: 122 degrees saturated temperature @ 176 PSI, rear liquid line was 93 degrees. This equals 29 degrees of sub cooling.

All of the above data was recorded while traveling at 60 MPH, 89 degrees ambient temperature, and 53 degrees outlet temperature on the rear A/C system. Also keep in mind the system was at least finally putting cool air out when all of this was done, and the length of the lines that reach to the rear evaporator have to be taken into consideration, I would think.

If needed, I can surely try my best to insulate the thermocouples and get these readings from the front evaporator, while the outlet temperature is 70+ degrees and not getting any cooler. Once I can get moving down the road the outlet temp starts to drop, but otherwise when sitting in crawling traffic on a 95 degree day I can't get cooler than 70+ degrees. If you'd like me to try to get those measurements let me know.

Thanks again Stamp, I really appreciate the help you've provided so far.
 

stamp11127

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Your first video tells the entire story. In order for the compressor to reach that high of pressure (425+) it can be only a few things:
1) restriction on the high side - oil slug, too much oil, pinched line
2) overcharged
3) txv slammed shut - puts the low side in a vacuum or very low pressure while the high climbs

When you changed components what did you flush the lines to the rear with?
FYI - I'm chicken sheet around high pressure and stop the system when it gets close to 350psi. We have had a few compressor safeties lift with student vehicles and what a mess that makes.

Your static pressure may indicate a slight overcharge but not enough for that high side reading and the initial low side reading once you turn the system on (which is high).

When you installed each component did you add the pag oil to each component or dump all of it in the compressor?

The low and high pressure readings when the ac is first started indicate the system is overcharged by volume. If there is anything left in, such as oil, the volume left for the refrigerant is less and increases pressure when the correct amount of refrigerant is added.

To prove if this is happening you should recover the system & note the oil amount removed. Recharge starting at something like 30oz of r134, don't add oil then run the system for 5-10 minutes to stabilize and record the pressures. Watch the low side gauge, if it drops to the low 20's the low pressure switch will open and disengage the compressor. Keep adding 1oz of refrigerant until the compressor stays running. As they say here in the south "you wana sneak up on it". You are looking for a low side pressure of 35-37 at idle.

Once the low side is "right" take a look at the high side pressure.

Ambient temp should be around the high 80's and in the shop or shade.

If the low side sucks down close to the mid to high 30's then it is a capacity issue between the amount of oil and refrigerant.
 
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AGrayson84

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Stamp, thanks a ton for taking the time to watch those videos and give me such a detailed response!

When I flushed both front-to-rear line sets I used probably as much as 1/2 cup per line of the Johnsen's A/C flush solvent (https://www.amazon.com/Johnsens-6545-6-Flush-32-oz/dp/B001DKPJW0). I blew the flush through the lines with 90 PSI of dry air (I have a moisture separator on the air line). I did maybe 1/4 cup per line first, and followed behind that with another 1/4 cup or so per line, once no more liquid was blowing out the opposite end. After the second bit of flush was sprayed through the lines I continued to blow the lines with dry air for another 30 seconds or so each. There was definitely no flush solvent coming out prior to the 30 seconds of dry air, I just chased it with nothing but dry air to be safe. I then left the front-to-rear line sets open for around 24 hours to dry any residual solvent, before installing my compressor, uncapping the new receiver/drier lines, bolting the connections together with new o-rings, and filling the system with PAG oil.

For the PAG oil, I did pour all 14 oz. right down into the compressor, via the suction line that attaches directly to the compressor. I was told that it was fine to do it that way, because the compressor would distribute the PAG oil once the system gets running. Was that not necessarily accurate?

I'll definitely try the method of recovering and adding refrigerant, one ounce at a time, using the method you described.

For clarification, would you mind explaining the last sentence? "If the low side sucks down close to the mid to high 30's" ...I just want to make sure I understand what I need to do there. In order, I understand I need to fill the system 1 oz at a time via the suction port until I am at 35-37 PSI at idle on the suction/low side. If I just finished charging the system to 35-37 PSI at idle, what does it mean when you say if the low side sucks down to that same amount (35-37 PSI)?? Thanks again Stamp!!!!!!

-Andrew
 

stamp11127

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The txv is the point where the high pressure and low pressure meet. When everything is correct you usually will see the low side pressure in the 30's and the high side pressure running between 150—225. The compressor is designed to pump/compress vapor not liquid. Putting that much oil in the suction side was a risk. Our oil injectors only hold 2oz, on a basically new system like yours we teach the students to add the oil to each component. Your condenser and receiver/drier are probably loaded with the oil you added and would explain the initial high readings. Keep your fingers crossed that the valves in the compressor aren't shot from adding the oil. If they crack some of the high side pressure leaks to the low side.

Start with a lower charge amount so that the system is under charged, say 35oz. Run the system and observe the pressures. Add refrigerant 1 or 2 oz at a time to bring the low side pressure within the "normal range" with the engine running. Wait a few minutes for the system to stabilize.

Fill low side vapor only. Don't fill on the high side even though the unit will allow it.

Once you have the low side where we want it (35-37psi) note the high side pressure. It should be under 250psi. Ambient temp should be around 85-90 for these numbers. No need to run the electric fans unless the fan shroud is missing.

FYI - When running the system don't rely on the high side switch to disengage the clutch, turn the ac switch off just shy of 350 psi. Repeat as necessary.

Since the system hasn't been opened you can do the 15 min wonder vacuum. We are after pressure readings and how much oil comes out right now. You may want to repeat the recover/recharge process a few times to get most of the oil out. Once it is running correctly add oil back in with an oil injector but only put in 70% of the recommended amount.

What weight pag oil did you use?

If you make additional videos please move the camera closer to the gauges so that it is easier to read on a small screen.

Flush - we usually blow through a full can or two when flushing the evap and condenser so there may have been some oil still in the lines. The lines can hold a considerable amount of oil and a half cup of flush may or may not completely flush the line.
 
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AGrayson84

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Thanks for the explanation on PAG oil. So I guess what I don't understand is that if the initial readings are a bit but then they come down.... does that not mean that once the pressure does come down that the PAG oil has then been more evenly distributed throughout the system? If so, what causes it to collect back in the condenser and receiver/drier again all the time? That's definitely not the first time I've had those initial high side pressures that high after firing up with the gauges attached. Prior to the latest round of replacing components, I had driven the car for 2 months with the A/C running probably at least half of the time prior to that.... then did an evac, vacuum, and recharge and it was still doing the same immediately after firing up the engine and turning the A/C on. The engine bay was pretty heat-soaked at that time, so we put a shop fan in front of the condenser after a solid 1-2 minutes of the high side pressures being 300+ PSI, and the high side pressures plummeted to right within spec. So that's when we decided the condenser must have need more air flow when parked, which is what lead me to the idea of installing those electric puller fans. Perhaps it was just coincidence that the pressures dropped once we put the fan in place.... and maybe the system just overcame that initial buildup of PAG oil?????

I'll definitely try to prevent the system from reaching 350 PSI. Should I wait 30 seconds between cycling the compressor off and back on, or anything?

I used PAG 46, which apparently is what is called for on these trucks. I used the dyed stuff, if that matters. Used one brand the first time, and another brand this second time after replacing parts again.

Unfortunately I no longer have a zoom lens, and that was the closest I could get the camera with the tripod to the gauge set, but I do have an actual video camera I can try to use next time that has zoom. Sorry about that.... I wasn't considering the fact that someone might not be using more than a mobile device to watch the video. If the battery is acting up on my actual video camera I'll try to move the gauges closer somehow... I'll figure something out :)

Oh regarding flushing things.... the evaporators and condenser were new this time around. New evaporators, condenser, receiver/drier, muffler line, etc. So all I literally flushed and blew clean were just the lines themselves that run front to rear. Both ends of the suction and both ends of the liquid line were open, not connected to anything at all. Once I flushed and blew them clean, I left them disconnected overnight to finish drying out (the solvent is supposed to be quick-drying solvent anyway). The next day I removed the factory shipping plugs from the new evaporators, installed the TXV's, installed the condenser and receiver/drier, and connected everything up... so literally no other component was flushed since everything else was new. And I left both ends of the receiver/drier capped from the moment I unpacked it out of the box, till the moment it was ready to be connected to the condenser and other line set. It was the last thing to remove the plugs from and connect up, and was open to the atmosphere for maybe 10-15 minutes tops. It didn't get connected until everything else was sealed up, so shouldn't be any moisture issues with that.

Thanks Stamp!
 

stamp11127

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The initial reads aren't a bit off, they are way out of the ballpark.
The receiver /drier is a collection point for the oil/refrigeration mix.

Flushing:
Think about this, if you lay a garden hose straight out on the ground with both ends open, would the flush clean the entire surface of the hose or just the bottom portion of the hose?
Only if you blew a large amount of flush under high pressure. You would have to pump a volume larger than the interior of the hose could handle. So is there any contamination still in your system? Probably, especially if a sealer was added in the past.

You have a restriction on the high side - plain and simple. Now what is causing it and where? Anything between the txv and compressor can. Before tearing into the system it is easy to check to see if it is charge related.

The pressure should come down immediately after cutting off the ac, as long as the high side isn't at a dangerous level you can turn it back on.

You should see immediate results with increased airflow through the condenser.
 
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wahew1

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Here are a couple pages out of Ford service manuals that may help.


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