Low side normal /high side low stumped

[DetroitAC]

I have just a couple thoughts to add:
I wouldn’t worry about the high side pressures being too low. They are too low because you don’t have very much cooling, the pressure should be low. If you get good AC performance back the pressure will go up. It’s like ordering 20 pieces of McNuggets and getting only 10, but hmm, that doesn’t seem like it’s heavy enough, let’s put it on a scale so we can get some data. I’m just kidding around, but I think you should focus on the low side and getting better cooling performance.

I wouldn’t change to a bigger orifice if your suction pressure is already too high (and thus too warm), bigger OT will make the problem worse. I was working at Visteon (they designed this) when this system was launching, I didn’t work on it, everything they did was ancient stone age technology even back then, vacuum actuators! One step of OT change isn’t a big deal, there is some fine tuning to be done there, but you have a larger problem.

The compressor is a plain Jane FS-10, should be cheap to get a good quality NEW unit. I’m not saying you need it, I can’t tell, but they are cheap I would think. It’s also an easy design to duplicate with aftermarket NEW compressors, I wouldn’t worry about a good brand aftermarket to replace an FS-10.

14oz oil is A LOT, were all your components internally flushed? I hope there wasn’t also existing oil in components.
Have you tried sneaking up on the refrigerant charge slowly or taking some out? An slightly overcharged system would work pretty much like you’re describing.
Is the rear TXV working? Is the suction line from the rear cold where it exits the body, but kinda warmish where it joins the main suction line?

[Excursion2001]

So I should put the factory one back in because the different OT will cause the txv to function different?

Honestly don't know, but i don't believe an O/T is able to interfere with a TXV since it can't modulate flow. Unless you get the OT so oversized that you end up starving the rear TXV, but that's highly unlikely, front won't cool at all. However, a stuck open rear TXV is surely able to play havoc with low side pressures and cooling in a dual system. A sure way to get a H-block TXV to either snap shut or throttle a bit (depending upon the MOP setting) is to get freeze spray on its disc. Suction doesn't seem to drop when you do that, you either have a stuck open TXV, or one with a severely worn superheat spring which is now flooding the rear evap all the time (and getting the suction abnormally up as a whole, preventing proper operation of the front system) instead of doing its superheat control thing.

Remember, a flooded evap won't be cool since the evaporation pressure is too high for actual cooling to take place. Most auto TXVs control charges are deliberately calibrated to start flooding the evap once it gets cold enough for a reason, and that's to stop the evaporator from icing up and blocking air flow (can list all the relevant Japanese Nippondenso/Fujikoki/TGK patents if needed and it hasn't got nothing to do with variable displacement comps; that mainly began as EPR related research meant to improve the defroster's performance in cool and wet Asian weather, and then got applied to basically any modern TXV MVAC system, even ones with fixed displacement comps). That's good as long as it isn't flooded when it has to actually deal with a heat load. In that case, things will stay warm and the comp will also be taking a real beating, having to deal with liquid slugs 100% of the time (and not right before it cuts off due to the evap's temp probe). Real cooling and also good enough oil return and compressor cooling comes from the right evaporator superheat (that is positive and slightly above 0, in a stable manner).

I replaced the txv in the rear when I rebuilt this unit you think that since this goes on multiple platforms you think it needs to be adjusted ? Or think the txv it was just bad from the start ? And I did some more research about ac recovery and I found that loading ac as a liquid on the suction side if it’s too much it will sludge the system and I think I did this when I was loading freon in the truck when I got everything together you think oil pooled up in somewhere ? And I did let some Freon out and it didn’t seem to help really

[Excursion2001]

I have just a couple thoughts to add:
I wouldn’t worry about the high side pressures being too low. They are too low because you don’t have very much cooling, the pressure should be low. If you get good AC performance back the pressure will go up. It’s like ordering 20 pieces of McNuggets and getting only 10, but hmm, that doesn’t seem like it’s heavy enough, let’s put it on a scale so we can get some data. I’m just kidding around, but I think you should focus on the low side and getting better cooling performance.

I wouldn’t change to a bigger orifice if your suction pressure is already too high (and thus too warm), bigger OT will make the problem worse. I was working at Visteon (they designed this) when this system was launching, I didn’t work on it, everything they did was ancient stone age technology even back then, vacuum actuators! One step of OT change isn’t a big deal, there is some fine tuning to be done there, but you have a larger problem.

The compressor is a plain Jane FS-10, should be cheap to get a good quality NEW unit. I’m not saying you need it, I can’t tell, but they are cheap I would think. It’s also an easy design to duplicate with aftermarket NEW compressors, I wouldn’t worry about a good brand aftermarket to replace an FS-10.

14oz oil is A LOT, were all your components internally flushed? I hope there wasn’t also existing oil in components.
Have you tried sneaking up on the refrigerant charge slowly or taking some out? An slightly overcharged system would work pretty much like you’re describing.
Is the rear TXV working? Is the suction line from the rear cold where it exits the body, but kinda warmish where it joins the main suction line?

How would I tell if the compressor is shot ? I flushed everything really good before I put everything together and both suction lines are cold . Iv tried to let a little out to were the low side should be at and no change .

[bohica2xo]

Open the doors put the cabin fan(s) on highest speed and raise the engine RPM to 1500+

Observe the high side pressure at maximum load. If it is below 2.5 times the ambient temperature, temporarily block the condenser air flow and test again.

If the compressor won't hit 300 psi on a 100f day it is tired.

[Excursion2001]

Open the doors put the cabin fan(s) on highest speed and raise the engine RPM to 1500+

Observe the high side pressure at maximum load. If it is below 2.5 times the ambient temperature, temporarily block the condenser air flow and test again.

If the compressor won't hit 300 psi on a 100f day it is tired.

Ok I’ll do that and report back

[DetroitAC]

TXV should be OK, I can't know for sure, but if you've changed it I'd look elsewhere.

We already know the high side isn't very high, in fact it's the title of the thread, go ahead and weigh those chicken nuggets again

I'm at a bit of a loss about what it could be, maybe too much oil, maybe weak compressor. If an FS-10 breaks a few discharge valves it will still keep working, they also have ringed pistons, they can wear out if there is debris in there.

[Excursion2001]

Open the doors put the cabin fan(s) on highest speed and raise the engine RPM to 1500+

Observe the high side pressure at maximum load. If it is below 2.5 times the ambient temperature, temporarily block the condenser air flow and test again.

If the compressor won't hit 300 psi on a 100f day it is tired.

Ok so I did the test . So my low side dropped when the rpm was set at 1500 and I blocked off the condenser with a trash bag when I did this both low side and high side very quickly reached 330 psi for high side and about 60-65 psi on the low side as when I bled some off the Freon off , oil was coming out of the low side

[Excursion2001]

Aftermarket TXV can be basically badly machined useless Chinese junk if unlucky. I tell people to buy (and refurbish too. All it takes is some freeze spray, some DEC PAG oil, some q-tips and some dry contact cleaner to flush any crud/dye/old oil out) second hand TXVs if they can't lay their hands on OEM ones (mostly made in Japan Denso) for a reason.

Well it was a four seasons one I think I threw the old one away

[bohica2xo]

Sounds like the pump is still capable, what was the ambient during the test?

And what did the low side drop from / to?

[Excursion2001]

Sounds like the pump is still capable, what was the ambient during the test?

And what did the low side drop from / to?

It was 105 when I bled some pressure off cause it was slightly to high on the low so I got it to 55 psi then I ran the test when I did the test my low side dropped to about 30psi and my high side stayed the same about 230 psi and that was with the condenser not blocked off. When I blocked off the condenser the low side shot up to about 70psi and the high side shot to 330psi before I pulled the trash bag off