Automotive Air Conditioning Information Forum

Hi all. Brand new here and starting off with a question. Thanks in advance for your time and help!

I recently replaced the ac system in my 2002 Tundra. I had a shop evacuate the R-134a and then I replaced the compressor, condenser, expansion valve, and receiver dryer myself. When everything was closed back up, I pulled a vacuum on the system for a little more than an hour. I closed the high and low valves at the gauge, shut off the vacuum pump and then because I had other things to do, I left it for about 4 hours under vacuum. The dial at the gauge showed nearly 30 in. Hg the whole time. However, here’s where I messed up. I thought I had both the high and low side connected and open but it turns out, I’m pretty sure the valve at the high pressure inlet was closed, meaning I was only pulling a vacuum from the low side.

I noticed the error because when I went to charge the system, I was not getting any pressure reading on the high side gauge. I went to check the connections and sure enough the valve at the high-pressure inlet was closed.

Of note, I forgot to add PAG oil when I replaced the condenser so when I had the receiver dryer off, I turned on the vacuum pump on the low side and was able to suck the oil into the system via the line that goes from the dryer through the expansion valve to the evaporator. My thought is that if the vacuum is passing from the low-pressure side through the expansion valve to the high-pressure side, it should make it through the receiver dryer and the condenser back to the compressor after everything is hooked back up.

My question is, do I need to go back and have the shop recover the refrigerant, pull another vacuum, and then recharge the system? Or, should the process I took be enough to pull the moisture from the system. Also, if there is likely moisture in the system now, do I need to replace the receiver dryer again? FWIW, the system is cooling to 44-45 degrees and seems to be working fine.

The way I read your post. You ended up charging the system back up without it in a vacuum? If that is the case, the system needs to be charged into a vacuum.

A lot to discuss here.

Let's start with the specs for your 2002 Tundra: 22 ounces net weight of R-134a, and 7.75 fluid ounces of PAG-46 oil.

Newbie47 wrote: Tue May 27, 2025 1:53 pm I recently replaced the ac system in my 2002 Tundra. I had a shop evacuate the R-134a and then I replaced the compressor, condenser, expansion valve, and receiver dryer myself. When everything was closed back up, I pulled a vacuum on the system for a little more than an hour. I closed the high and low valves at the gauge, shut off the vacuum pump and then because I had other things to do, I left it for about 4 hours under vacuum. The dial at the gauge showed nearly 30 in. Hg the whole time. However, here’s where I messed up. I thought I had both the high and low side connected and open but it turns out, I’m pretty sure the valve at the high pressure inlet was closed, meaning I was only pulling a vacuum from the low side.

Normally, a system is evacuated with the vacuum pump connected to the yellow hose from the Manifold Gauge Set (MGS), the red hose is connected to the high side (HS) of the system, and the blue hose is connected to the low side (LS) of the system. Both the HS and the LS adapters on the service ports will be fully open (thumb-wheels turned fully clockwise), and the hand-wheels on the MGS will also be fully open (turned fully counter-clockwise).

Although you didn't have the HS open to vacuum during evacuation, the system will still be evacuated—but more slowly. Under these conditions, running the vacuum pump for longer than one hour would be prudent.

Newbie47 wrote: Tue May 27, 2025 1:53 pm I noticed the error because when I went to charge the system, I was not getting any pressure reading on the high side gauge. I went to check the connections and sure enough the valve at the high-pressure inlet was closed.

You would charge the system with refrigerant vapor (can upright) only through the LS. The HS must remain closed during charging.

Newbie47 wrote: Tue May 27, 2025 1:53 pm Of note, I forgot to add PAG oil when I replaced the condenser so when I had the receiver dryer off, I turned on the vacuum pump on the low side and was able to suck the oil into the system via the line that goes from the dryer through the expansion valve to the evaporator. My thought is that if the vacuum is passing from the low-pressure side through the expansion valve to the high-pressure side, it should make it through the receiver dryer and the condenser back to the compressor after everything is hooked back up.

How much oil did you add using that unconventional method? Unfortunately, by sucking-in the oil like that, you also unknowingly introduced air and moisture into the system, which will need to be removed.

Since you replaced the compressor, condenser, receiver/dryer (R/D), and the thermostatic expansion valve (TXV), did you thoroughly solvent-flush the evaporator and any lines without mufflers (can-like devices in the line) of old oil? (Lines with mufflers can't be flushed and must be replaced.) If not, you should have.

Did the old compressor disintegrate internally? If that's the case, it's especially important that the aforementioned components be thoroughly flushed.

In addition, you should have drained-out the oil in the new compressor, and either refilled it with the correct amount of 7.75 fluid ounces, or oil-balanced the system, which has been discussed in detail a number of times on this Forum. Without starting from a "dry" system and filling it to specs, the amount of oil in the system cannot be known.

Newbie47 wrote: Tue May 27, 2025 1:53 pm My question is, do I need to go back and have the shop recover the refrigerant, pull another vacuum, and then recharge the system? Or, should the process I took be enough to pull the moisture from the system. Also, if there is likely moisture in the system now, do I need to replace the receiver dryer again? FWIW, the system is cooling to 44-45 degrees and seems to be working fine.

As mentioned, the amount of oil in the system is not currently known. If too little, the new compressor won't last very long due to lack of lubrication. If too much, the oil will take-up room that the refrigerant would otherwise occupy, and the system won't operate properly, especially with the onset of hot summer days.

How did you charge the system, by weight or pressure? What was the ambient temperature? What were the pressures at ~1,800 RPM when you finished charging it?

The only correct way to charge any system is by weight into a well-held vacuum, as mentioned in the previous post. Also, because the system now has air and moisture in it, the R/D would have to be replaced again.

Tim wrote: Tue May 27, 2025 6:39 pm The way I read your post. You ended up charging the system back up without it in a vacuum? If that is the case, the system needs to be charged into a vacuum.

I apologize for the odd way I phrased my order of operations. I sucked air and oil into the system while the R/D was off and before I pulled a vacuum on the system. After I added the oil and closed the system by installing the new R/D, then I pulled the vacuum and after it held for 4 hours I added the refrigerant. If it still sounds like I charged the system without a vacuum, please correct me so I can fix the issue. Thanks!

JohnHere wrote: Tue May 27, 2025 7:45 pm A lot to discuss here.

Let's start with the specs for your 2002 Tundra: 22 ounces net weight of R-134a, and 7.75 fluid ounces of PAG-46 oil.

Normally, a system is evacuated with the vacuum pump connected to the yellow hose from the Manifold Gauge Set (MGS), the red hose is connected to the high side (HS) of the system, and the blue hose is connected to the low side (LS) of the system. Both the HS and the LS adapters on the service ports will be fully open (thumb-wheels turned fully clockwise), and the hand-wheels on the MGS will also be fully open (turned fully counter-clockwise).

Although you didn't have the HS open to vacuum during evacuation, the system will still be evacuated—but more slowly. Under these conditions, running the vacuum pump for longer than one hour would be prudent.

I definitely agree there is a lot to unpack and I really appreciate you taking the time to address it.

So if I accidentally pulled the vacuum from just the low side and only for an hour but it maintained a constant vacuum for 4 hours do you think the system was not fully vacuumed? It would make sense to me if I only got to 28 in Hg or if it started at 29 in Hg but dropped to 28 in Hg that the system was not fully vacuumed, but since it was nearly 30 in Hg and maintained for 4 hours I would think it was sufficient. If I'm wrong, I'm happy to be corrected from an expert.

JohnHere wrote: Tue May 27, 2025 7:45 pmYou would charge the system with refrigerant vapor (can upright) only through the LS. The HS must remain closed during charging.

This was the process I used. High side closed at both the manifold and the service port and charging through the yellow hose into the low side. I was thinking that because the valve at the service port was closed, that is why the high side manifold gauge was not reading any pressure as I was charging the system. When I opened the valve at the high side service port (but not the high side on the manifold) the high side gauge started registering pressure.

JohnHere wrote: Tue May 27, 2025 7:45 pmHow much oil did you add using that unconventional method? Unfortunately, by sucking-in the oil like that, you also unknowingly introduced air and moisture into the system, which will need to be removed.

I added 60 cc of oil per the service bulletin I was following. 40 for the new condenser and 20 for the new R/D. Per your discussion below, I understand now why that's not going to be accurate. As to adding moisture to the system, as I stated in my reply to Tom. I phrased my order of operations poorly. The vacuum was pulled after the oil was added and the system was closed up by installing the R/D. If I'm still not understanding what you're saying, let me know as I would like to fix my errors.

JohnHere wrote: Tue May 27, 2025 7:45 pmSince you replaced the compressor, condenser, receiver/dryer (R/D), and the thermostatic expansion valve (TXV), did you thoroughly solvent-flush the evaporator and any lines without mufflers (can-like devices in the line) of old oil? (Lines with mufflers can't be flushed and must be replaced.) If not, you should have.

Did the old compressor disintegrate internally? If that's the case, it's especially important that the aforementioned components be thoroughly flushed.

No, I did not flush out the system or replace lines with mufflers, but at least it wasn't a catastrophic compressor failure. The clutch failed on the old one and rather than rebuild it I opted to replace the whole thing.

JohnHere wrote: Tue May 27, 2025 7:45 pmIn addition, you should have drained-out the oil in the new compressor, and either refilled it with the correct amount of 7.75 fluid ounces, or oil-balanced the system, which has been discussed in detail a number of times on this Forum. Without starting from a "dry" system and filling it to specs, the amount of oil in the system cannot be known.

As mentioned, the amount of oil in the system is not currently known. If too little, the new compressor won't last very long due to lack of lubrication. If too much, the oil will take-up room that the refrigerant would otherwise occupy, and the system won't operate properly, especially with the onset of hot summer days.

I definitely concede that I don't know how much oil is in the system. The compressor I bought came prefilled with 4.8 oz. I added 2.1 for the new R/D and new condenser. So 6.9 oz, but I have no idea how much remained in the lines or evaporator. It stands to reason to me that the system is over filled rather than under filled because I think (perhaps in error) that there is more than 0.85 oz of oil in the lines and evaporator. If that is the case, is the consequence just less efficiency due to too much oil causing an over charged system, or are there more serious issues that will arise?

JohnHere wrote: Tue May 27, 2025 7:45 pmHow did you charge the system, by weight or pressure? What was the ambient temperature? What were the pressures at ~1,800 RPM when you finished charging it?

The only correct way to charge any system is by weight into a well-held vacuum, as mentioned in the previous post. Also, because the system now has air and moisture in it, the R/D would have to be replaced again.

I charged the system by weight. I hooked up the first can to the yellow line with high and low dials closed at the manifold and then purged the yellow line. I opened the low side to charge the system and according to the scale I was using (measures to 1/8 oz.) I got nearly 12 oz from that can. I then closed the LS line and hooked up the second can and purged the yellow line again because I wasn't sure if air had been introduced and since I had more refrigerant than I needed, this seemed like the safe approach. I added a little over 9 oz from that can. The scale indicated 9.25 oz. I shot for 21 oz. because the document I was following said 21.16 oz plus/minus 1.76 oz, so I thought that a target of 21 oz. would give me the best chance of landing within range.

Since the range for the refrigerant is up to 22.92 oz and I only put in about 21 oz. would that help offset the negative consequences of having too much oil in the system?

Newbie47 wrote: Tue May 27, 2025 10:39 pm So if I accidentally pulled the vacuum from just the low side and only for an hour but it maintained a constant vacuum for 4 hours do you think the system was not fully vacuumed? It would make sense to me if I only got to 28 in Hg or if it started at 29 in Hg but dropped to 28 in Hg that the system was not fully vacuumed, but since it was nearly 30 in Hg and maintained for 4 hours I would think it was sufficient. ... .

It doesn't matter how long the system sat idle without the vacuum pump running. The 4 hours means that the system held vacuum for that long, nothing more. The only way that air and moisture are drawn out of the system is if the vacuum pump is connected to the system and is running.

So to answer your question, chances are that air and moisture remained in the system after you evacuated it for about one hour because the HS remained closed to the vacuum pump the entire time. How much air and moisture remain in the system, if any, is strictly guesswork.

Air, which is a non-condensable gas, can't be turned into a liquid (cannot change its state) under normal Mobile Vehicle Air Conditioning (MVAC) conditions, as R-134a can. Therefore, if any air is left behind after evacuation, cooling will suffer.

Moisture is equally as bad, but in a different way: It will react with the oil and create acids. Of course, moisture by itself will also corrode the metallic parts of the system from the inside.

Newbie47 wrote: Tue May 27, 2025 10:39 pm This was the process I used. High side closed at both the manifold and the service port and charging through the yellow hose into the low side. I was thinking that because the valve at the service port was closed, that is why the high side manifold gauge was not reading any pressure as I was charging the system. When I opened the valve at the high side service port (but not the high side on the manifold) the high side gauge started registering pressure.

You figured it out correctly. With the HS adapter's thumb-wheel closed at the service port, the MGS won't register any pressure on that side whether the hand-wheel on the MGS is open or closed. But with the thumb-wheel on the adapter fully open and the hand-wheel on the MGS fully closed, as it should be during charging, the HS gauge will still register the HS pressure.

Newbie47 wrote: Tue May 27, 2025 10:39 pm I added 60 cc of oil per the service bulletin I was following. 40 for the new condenser and 20 for the new R/D. Per your discussion below, I understand now why that's not going to be accurate. As to adding moisture to the system, as I stated in my reply to Tom. I phrased my order of operations poorly. The vacuum was pulled after the oil was added and the system was closed up by installing the R/D. If I'm still not understanding what you're saying, let me know as I would like to fix my errors.

Okay, what you're doing, in effect, is oil-balancing the system—40cc (or about 1.4 fluid ounces) for the new condenser, and 20cc (or about 0.7 fluid ounce) for the new R/D. Those amounts sound about right.

"Assuming" that the compressor had actually been pre-filled from the factory with 4.8 fluid ounces, results in about 6.8 fluid ounces, not including the oil left in the lines (usually a trace amount) and the evaporator (usually about 0.5 fl. oz.), giving a grand total of 7.3 fl. ozs. out of the 7.75 fl. ozs. specification for your vehicle, which is about 0.5 fl. oz. short.

However, the amount that the compressor contained is still unverified. It might have had 4.8 fl. ozs. in it, but it might have had more, or less. The only way to gauge how much it contained would be to drain-out whatever was in it originally and measure it. Then you could replace the drained-out oil with fresh PAG, adding about 0.5 fl. oz. to make up the shortfall (oil-balancing once again).

Or, to simplify the process, you could've subtracted 0.5 fl. oz. (the estimated amount in the evaporator) from 7.75 fl. ozs. (7.25 fl. ozs. or 215cc), added the latter amount to the compressor only, (skipping putting any oil in the condenser and R/D), and call it done.

Newbie47 wrote: Tue May 27, 2025 10:39 pm I charged the system by weight. I hooked up the first can to the yellow line with high and low dials closed at the manifold and then purged the yellow line. I opened the low side to charge the system and according to the scale I was using (measures to 1/8 oz.) I got nearly 12 oz from that can. I then closed the LS line and hooked up the second can and purged the yellow line again because I wasn't sure if air had been introduced and since I had more refrigerant than I needed, this seemed like the safe approach. I added a little over 9 oz from that can. The scale indicated 9.25 oz. I shot for 21 oz. because the document I was following said 21.16 oz plus/minus 1.76 oz, so I thought that a target of 21 oz. would give me the best chance of landing within range.

Sounds like you charged it correctly.

Newbie47 wrote: Tue May 27, 2025 10:39 pm Since the range for the refrigerant is up to 22.92 oz and I only put in about 21 oz. would that help offset the negative consequences of having too much oil in the system?

Bear in mind that you most likely charged the system with a bit less than 21 ounces because some of the refrigerant weighed by the scale actually remained in the hoses, unless you purged the hoses into the system. Most shade-tree mechanics forget to do that and wind up with a slightly low charge. Always go for the upper limit in charging. That way, if you forget to purge the hoses, you'll still be within the manufacturer's specification.

"Assuming" (there's that word again) that the new compressor actually contained 4.8 fl. ozs. of oil, I think that the system is slightly low on oil, which I doubt will affect anything.

It was a brand-new compressor, not a rebuilt, right?

Thank you for the second reply. I was helping at a youth camp, so please don't take my delayed response as a sign of ingratitude. I am incredibly grateful you have taken so much time helping me understand the important details and overall process.

The system is working great right now, but the highest outside temperature has only been about 83 degrees, so I don't know what it will feel like when it's really put to the test this summer. I also forgot to mention that there's a little glass window over the R/D where you can see the refrigerant. The service bulletin I was following had a high level diagnostic process using that window and when I follow that, it says I have properly charged the system (Window is clear while system is running, bubbles form when system is shut off and then it goes clear again within a few seconds). Not sure how reliable that is, or if real technicians would completely ignore this method, but, there's that.

From your reply, I gather that IF the pump had the proper amount of oil, I should be close enough to not damage the system. In your experience, is it common for prefilled pumps to not have the proper amount of oil? Pretty crappy if it's common for them to not be properly prefilled. If I should have drained the pump and confirmed the amount of oil in it and then refilled with new PAG oil, what's the point of prefilled pumps? I should have just bought a pump and separate oil.

Also, you were correct that I didn't take into account the refrigerant left in the lines, so I'm probably under charged. Since I'm probably slightly short on oil and short on refrigerant, would you suggest I add some oil through the low pressure port line and another oz. of refrigerant, or would it be best to have the refrigerant evacuated, pull a vacuum using the correct process, and then add the half oz of oil and correct charge?

Thanks again! I'll be making a donation to your site to show my appreciation!

Thank you for the support.

Newbie47 wrote: Mon Jun 02, 2025 9:09 am ... . I was helping at a youth camp, so please don't take my delayed response as a sign of ingratitude. ... .

Not at all. Life happens

Newbie47 wrote: Mon Jun 02, 2025 9:09 am I was following had a high level diagnostic process using that window and when I follow that, it says I have properly charged the system (Window is clear while system is running, bubbles form when system is shut off and then it goes clear again within a few seconds). Not sure how reliable that is, or if real technicians would completely ignore this method, but, there's that.

That sight glass is a hold-over from R-12 refrigerant days (in Toyota's case, before 1994) and isn't a reliable indicator when charging with R-134a. My guess is that Toyota still had some of the older-style receiver/dryers on hand, delayed changing the tooling (for cost purposes), and simply continued using the R/D's with a sight glass. However, the desiccant inside the R/D is different for R-134a, which the company undoubtedly changed over for the newer cars (at that time). In the "old days" of R-12, techs did use the sight-glass method. But the only acceptable way to charge or re-charge a system nowadays is by weight. You charged it correctly that way.

Newbie47 wrote: Mon Jun 02, 2025 9:09 am From your reply, I gather that IF the pump had the proper amount of oil, I should be close enough to not damage the system. In your experience, is it common for prefilled pumps to not have the proper amount of oil? Pretty crappy if it's common for them to not be properly prefilled. If I should have drained the pump and confirmed the amount of oil in it and then refilled with new PAG oil, what's the point of prefilled pumps? I should have just bought a pump and separate oil

If the manufacturer stated that the compressor contained 4.8 fluid ounces from the factory, we'll have to presume that's the case. Pros typically verify the factory-fill, if any, by draining and refilling the compressor. Additionally, some systems might require more or less oil in the compressor, depending on a system's capacity. Only way to gauge that is to drain it out and measure.

Some compressors ship "dry," others come with "shipping oil" that must be drained and refilled, and still others come with at least some PAG oil in them, like yours. Depends on the manufacturer.

Newbie47 wrote: Mon Jun 02, 2025 9:09 am Also, you were correct that I didn't take into account the refrigerant left in the lines, so I'm probably under charged. Since I'm probably slightly short on oil and short on refrigerant, would you suggest I add some oil through the low pressure port line and another oz. of refrigerant, or would it be best to have the refrigerant evacuated, pull a vacuum using the correct process, and then add the half oz of oil and correct charge?

At present, I doubt that the slight undercharge of both oil and refrigerant will make any difference. IMHO, I would leave it alone since you already have everything buttoned-up, charged, and ready to go for the summer. I would wait until such time that the system develops a leak (if ever) or experiences cumulative seasonal losses from the compressor shaft seal—enough that cooling is noticeably affected. At that time, you'll need to find the leak, change the R/D, evacuate, and recharge. Or, if there is no actual leak—just seasonal losses—recover, evacuate, and recharge to specs.

Thank you again for all your help, detailed responses, and background information! It's good to know the history of things so I can better determine what is relevant and what is not, and it's especially helpful to know that the sight glass is an unreliable method of diagnosing the system in the future. I'll keep an eye on things and follow your recommendations going forward. Thanks again!