A/C new install

m-35tom

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OK, new A/C install with gen2 evaporator, high side 225, low side 25, what should air from evap be? I barely get 65°. R134A
 

m-35tom

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Nope, that's not it. Same temp readings as 4 lb charge and 5 lbs. Pressure was too high at 275 and 45 so I went down to 4 lbs and high side is 200 but low side is 25, way to low for 134. Still blows 65° at 82° ambient. New gen 2 unit has been sitting for years.
 

Ronmar

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Low coolant or low coolant flow. Since your testing shows it isnt low coolant and with the high pressure split, Perhaps the TRV(Or somewhere else in the circuit) has an obstruction Which isnt letting the refrigerant flow properly... Are the condenser fans operating and giving good flow thru the condenser?
 
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simp5782

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Not enough air across the condenser.

I assume its 65 at idle sitting in the driveway? Not at road speed?

Did you insulate your ac hoses? This will help a ton and drop temps by about 15 degrees.

Or switch to R12. I did. 48 degrees at 92 ambient with 70% humidity
 

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m-35tom

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Low coolant or low coolant flow. Since your testing shows it isnt low coolant and with the high pressure split, Perhaps the TRV(Or somewhere else in the circuit) has an obstruction Which isnt letting the refrigerant flow properly... Are the condenser fans operating and giving good flow thru the condenser?
Inlet to condenser is very hot, outlet is almost at ambient temp so condenser is doing a great job, it is a very large condenser. 968 square inches. Air from evap is same temp regardless of engine rpm. I feel like the expansion valve is restricting the flow to much but everything is new.
 

Ronmar

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Inlet to condenser is very hot, outlet is almost at ambient temp so condenser is doing a great job, it is a very large condenser. 968 square inches. Air from evap is same temp regardless of engine rpm. I feel like the expansion valve is restricting the flow to much but everything is new.
Well you could pull the TRV, warm its bulb and back-flush it with compressed air...
 

m-35tom

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Yes it seems like it must be restricted. I suppose I could just take the lines off under the cab and do it there since the cab temp is at least 100°!! Maybe I could catch something coming out the inlet.
 

MAdams

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I'm having the same problem on my 7 ton. Low side pressure is 18psi, warm outlet air from evap and I charged the system to the correct 2.25lbs of 134a. I think my TXV is either bad or possibly backwards if that's possible. I didn't have the correct high side adapter for my gauge set

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m-35tom

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I started taking the case apart in the truck and the first thing I found was 34° at the header feeding the coil. And it looks like they allowed a huge amount of air to just go around the coil on the ends. I have 30 of these units so tomorrow I am going to take another apart to see how it was made. On the LMTV does the A/C only work on recirculate? Heater hoses are both cold so that is good. If I move the TXV bulb to a warmer spot the low side should come up meaning more refrigerant being fed to coil, right? And using more should lower high side?? As I said, my condenser is huge, my thought being to small is bad but never can be to big. Normal system holds 4.2 lbs?? So I figured 5 lbs, pressure will tell.
 

m-35tom

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Well air going around the evap isn't being chilled:)
Exactly. Now I am not yet positive of this but will know tomorrow. What do you think about relocating the TXV bulb to trick it into opening more? I would know if it works by the low side pressure.
 

MAdams

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Post a picture of your txv. I just found out some are adjustable with a brass screw on the bottom

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Third From Texas

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I'm kinda surprised that the gen2 kits hadn't ironed out these sort of issues.

I've been going back-and-forth with just building a system from scratch or using a surplus kit for simplicity. I know all the bits that I need, and where I can get the civilian equivalents but I figured that the surplus kit would be more plug-n-play friendly.

Now I'm not so sure.

Following
 

Ronmar

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Well if you can get all the air to pass thru the evap, you shouldn't have to relocate the bulb... one of the main functions of the TRV and its temp sensor/bulb is to keep the evap from freezing the condensed water On the evap...
 

m-35tom

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OK, found 3 things. There is a baffle so all the air does go through the evaporator coil. The A/C only works on recirculate. It does NOT use a TXV, it is an AXV. I think this was a very bad decision since with a high heat load it will actually cool less.
 

Ronmar

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Ok, well an AXV simply maintains outlet pressure on the evap. So either it is set too low(sure there isnt an adjustment screw on it, that is usually how the low pressure is set to match the flow). Or something else in the system is restricting the flow or the compressor isnt working to spec and the AXV is regulating the evap outlet pressure accordingly. Or it is broke/clogged...
 

m-35tom

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Ok, well an AXV simply maintains outlet pressure on the evap. So either it is set too low(sure there isnt an adjustment screw on it, that is usually how the low pressure is set to match the flow). Or something else in the system is restricting the flow and the AXV is regulating the evap outlet pressure accordingly. Or it is broke/clogged...
Would you agree that a TXV works much better than an AXV? There is a plug on the bottom of the block opposite the control diaphragm. Air out should be at least as low as 40° and maybe as low as 30° in my view. My car is 41° my M35 was 28°, all with 134A
 
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