REV Truck Air Conditioning

[T9000]

I finally got around to take the truck (1165A1) to a car shop to service the A/C and after they drained it, they filled with 3lb 5oz R134A (I forgot that it needed 3lb 8oz and having 3oz less should not be a big of an issue?).
Soon after starting the engine the cold air started coming out from the front vents and rear vents.
About 10-15 minutes later as I was driving, a big hissing noise starting to come from around the passenger front side and a little white vapor came out from under the hood by the windshield and the snorkel tube base as well as a little thru the front dash, passenger side (the shop was closing and could not go back right away, will have to wait until Monday).

After the hissing noise, the compressor, front and rear vent fans continued to work, but blowing only warm air.
It sounds like the R134A leaked out of the system and I am planning to get a R134A can with UV dye today and an AC manifold gauge set for both, high and low side, and see if I can find the leak.
A few questions:

1. There was no conversation about adding any PAG oil after they drained the system, is that something the shops do automatically? Does the PAG oil needs to be replaced or added also? (I saw some bulletin saying to add 10oz if the system is drained or the amount of PAG oil is unknown, does that sound right?)
2. I didn't pay attention and didn't ask if their R134A had any sealant added in it (they had a R134 can that looked about 20lbs, similar size to a small propane tank) and I presume the auto shops use the one without any sealants? (will call them to confirm on Monday)
3. In terms of troubleshooting where do you recommend I should start looking? It sounded like a large leak given the loud hissing sound, any indication what part(s) in that area could cause it?
4. Any other recommendations?

Thank you!

 

[NDT]

Ugh something failed big time. Maybe you can find out what blew out yourself. Look for oily spots in the area you described. If something like an evaporator coil blew, you will need to find that part and either replace it yourself or supply it to the shop. They won’t have access to military parts.

 

[86humv]

The pump is usually the first thing to fail.

 

[Retiredwarhorses]

If that much 134 leaked out that fast? its Going to be pretty obvious to find the failure point I’d assume.
you won’t need a UV dye…just take it back to the shop, they need find the leak, fix it…vacuum it back down and replace the 134.
if they are using a machine? The machine does everything automatically

 

[T9000]

Ugh something failed big time. Maybe you can find out what blew out yourself. Look for oily spots in the area you described. If something like an evaporator coil blew, you will need to find that part and either replace it yourself or supply it to the shop. They won’t have access to military parts.

There is something like an oil splash on under the hood above the compressor, not sure if it was there before...also the high side plastic red cap was covered in a grey residue.
It looks like maybe the compressor went out, and I am hoping is just the high side valve, but it's more like wishful thinking.

 

[T9000]

If that much 134 leaked out that fast? its Going to be pretty obvious to find the failure point I’d assume.
you won’t need a UV dye…just take it back to the shop, they need find the leak, fix it…vacuum it back down and replace the 134.
if they are using a machine? The machine does everything automatically

Yes, they used the machine and programmed the 3lbs 5oz in it, but wasn't sure if the machine knew to add PAG oil and how much.
I will call them tomorrow.

 

[T9000]

The pump is usually the first thing to fail.

I am hoping is not the compressor, the truck doesn't have that many miles or hours on it, but it looks like it could be.

 

[T9000]

I am still going to get some R134 with dye and the manifold gauges to do some troubleshooting myself, sorry but I can't resist

 

[T9000]

If that much 134 leaked out that fast? its Going to be pretty obvious to find the failure point I’d assume.
you won’t need a UV dye…just take it back to the shop, they need find the leak, fix it…vacuum it back down and replace the 134.
if they are using a machine? The machine does everything automatically

For my own education, why would the A/C system need to be vacuumed again if they just did it yesterday?
After fixing the leak, couldn't the system just be charged to the appropriate high & low pressures for the given ambient temperature?

Thanks!

 

[NDT]

Two reasons. When the system is opened to do the repair, air and humidity enters the system. Air is “non-condensable” meaning it can’t function as refrigerant. Moisture will cause corrosion inside the system.

 

[T9000]

One other thing I didn't mention because wasn't sure if I saw it correctly...after the shop recharged the AC system (using their machine) the high side gauge looked maxed out, which in theory that would be about 500psi?
I didn't feel that confident about the shop because when they brought the AC machine outside, the sun was so bright and they were struggling to see the correct settings on the screen, If they put 3lb 5oz of R134a, the pressure should not overshoot over 250psi or go anywhere close to 500psi, correct?

 

[NDT]

Right 500 psi way to high even at 100 ambient.

 

[TOBASH]

Air is compressible. All gasses are.

Air just liquifies at the wrong temp and pressure to be as efficient for a car compressor.

When air gets into the system, the compressor won’t be able to liquify the mixture properly, so the system won’t work efficiently.

When your system let go, air got in and will need to be purged.

When your system let go you also lost the lubricating oil, which now needs to be replaced.

 

[T9000]

Air is compressible. All gasses are.

Air just liquifies at the wrong temp and pressure to be as efficient for a car compressor.

When air gets into the system, the compressor won’t be able to liquify the mixture properly, so the system won’t work efficiently.

When your system let go, air got in and will need to be purged.

When your system let go you also lost the lubricating oil, which now needs to be replaced.

That's why I was asking about the oil.
The shop didn't seem to check about or add any oil after they vacuumed the system, they only added the R134a.
However, from what I read, only when a component like the compressor, condenser, etc. gets replaced, the oil needs to be replaced as well.
How would you determine when and how much oil to add?

 

[T9000]

Air is compressible. All gasses are.

Air just liquifies at the wrong temp and pressure to be as efficient for a car compressor.

When air gets into the system, the compressor won’t be able to liquify the mixture properly, so the system won’t work efficiently.

When your system let go, air got in and will need to be purged.

When your system let go you also lost the lubricating oil, which now needs to be replaced.

And thanks for the good explanation about the air, I get it now.

 

[T9000]

Quick update, I measured the low & high side at 15psi and 150psi, then I added some refrigerant and uv dye and the pressure stabilized at 40 & 225psi at around 80-85F outside temp. Right before, I washed the engine and the hood just to make it easier to observe any new splashing, leaking, etc.
I drove it around and the front and rear air is running cold, but so far I couldn't find any leaks (nothing around the compressor either), will check the pressure and for leaks again in a few days. Next, I will take it to the shop (different place) to drain/ vacuum the system again and refill it again.
Would it be possible that the shop overcharged the system and when the pressure increased too much, some of the refrigerant got released thru the high side valve?

EDIT: spelling

 

[REF]

Those numbers look like it is now over charged to me, on an 80 deg day I would expect to see maybe 20 over 180. From your description above, if it were your AC I would have expected the system to be empty from a blown hose or o ring. You may want to look over your cooling system if the coolant tank cap wasn't holding PSI or your vent tube was blowing, that could account for the amount of mist you were seeing in that area and the anti freeze would leave an oily looking spot. Did it smell sweet when this happened?

 

[T9000]

I went with the

Those numbers look like it is now over charged to me, on an 80 deg day I would expect to see maybe 20 over 180. From your description above, if it were your AC I would have expected the system to be empty from a blown hose or o ring. You may want to look over your cooling system if the coolant tank cap wasn't holding PSI or your vent tube was blowing, that could account for the amount of mist you were seeing in that area and the anti freeze would leave an oily looking spot. Did it smell sweet when this happened?

I used the numbers from this diagram (yes, my high side is a little higher by about 10%, but for testing purposes I thought it's OK, as I plan to vacuum it)

I understand what you mean about the coolant cap and I like your idea, it is just that the smell was like R134, which I recognized from the shop when they vacuumed/ drained the truck as some vapor was exiting from their vacuum pump.
The coolant cap is solid, never had any venting from there and I extended the vent tube all the way under the truck to eliminate the few occasional green drop splashes that used to show on the side wall when it was shorter.
There was a splash under the hood in the area above the compressor, but I am not sure if it wasn't there from before. I washed the hood and so far no other splashes are showing after driving it around with the AC running on high.
Will keep checking and thanks for the suggestions.

 

[Retiredwarhorses]

The R4 compressor has an over pressure valve IIRC…

 

[T9000]

The R4 compressor has an over pressure valve IIRC…

Aha! That would explain the venting and everything still working OK after.
Thank you!