Replaced ac evaporator now pressures are off

Hi,
I could use some help, it is getting hot in Florida. I replaced the ac evaporator on my 1987 V10. It has a Sandeson compressor. The system blew very cold but had a small leak at the connection by the orifice tube. I removed the 134a and thought I would replace the orifice tube while I had the system open at that location. The orifice tube would not come out. I tried everything and every tool with no luck. I bought the GPD evaporator and installed it. Vacuumed down the system and added 32 ounces of 134a. The ac blows cool, not cold, but the issue is the compressor does not cycle off now and the low side pressure is at 55 while the high side pressure is at 50. I did not add more 134 because I did not want to have the low side pressure go higher. Those pressures are at idle. As rpm increases the low side will drop to 40, but the high side does not change pressure. Any idea what is causing this issue?

I have to do the same thing on my 1985 and don't want to have the same problem a second time.
Thank you!

The pressure differential is at the orifice tube. One side from the condenser hot and the towards the evaporator cold. Low pressure, high pressure. Cold and hot. It sounds like either the orifice tube was left out or you have a bad pump. You mentioned a Sanden pump which normally would be found in a aftermarket system. Aftermarket systems typically have an expansion valve and a reciever drier. The factory system uses a orifice tube and a accumulator found close to the firewall. Either the expansion valve is stuck open or the orifice tube is missing. The Sanden pumps are pretty bulletproof. In most applications the orifice tube is found in the condenser unless there is a rear unit as a Suburban. Then it is usually in the liquid line headed towards the rear of the vehicle. If it is the condenser you replaced and not the evaporator the aftermarket condenser sometimes comes with or without the orifice.That would be my belief, the condenser came without

Loren has your answer. Simply the orifice tube holds the pressure. If the orifice tube is there, maybe it is damaged so pressure can pass around the small orifice. AC is not going to work if it can't build pressure.

Did you install an orifice tube in the new evaporator? They do not come with them installed.

With equal pressure you system is not doing anything. If the compressor clutch is engaged and that is what you have for pressures either your compressor is no good or you do not have a proper restriction.

Your pressure when the system is not attempting to operate should be close to what is in this chart. You may be a hair undercharged but that is not your issue right now. It may be once you get it operating correctly. A properly operating R134a system should see 30-35psi on the low side. You need to make sure you bring up the RPMs and have enough air moving through evaporator to get a good idea of proper function.

Since several of you seem to be A/C experts, I have an additional question.
- My '75 A/C was apparently a crossover year after they stopped using the TXV from '74.
- The '75 evaporator has an adapter for the orifice (Rockauto site has a picture), and the adapter appears to be a brass tube (about finger size) with an O-ring on the outside to seal to the evaporator, and a hole in the middle to insert the orifice tube.
- When I check the specs for the orifice tube and evaporator used in '76 it is completely different and it does not include the brass tube.
Bottom line - the the '75 A/C system seems to be a one-off solution, but replacement parts are available.

My system was converted to R134a/PAG years ago, and it works okay with a Ford blue orifice. However, it also seems to have a very slow leak that I would like to find. I have added leak detector in the past and I did not see telltale residue on hoses, condenser, etc. with the black light.
The only remaining original part of the system is the evaporator, so my plan is to add leak detector and then crack open the housing under the hood to check for any evidence of a leak in the evaporator.

Does this sound like a good solution to find a leak, or am I headed in the wrong direction? It does accomplish two goals at the same time, since I can check for leaks and also replace the orifice tube and accumulator before I recharge.

Thanks.

Leaks are easy, seepage is another story. Seepage will show up as an oily spot. You don’t need dye unless you want to distinguish one oily spot from the AC to another. Look closely, inspect both sides of the condenser, all the lines, look up on the underside of the hood for spray coming from the compressor. If you find nothing on the engine side of the firewall, you might be looking at the evaporator. The evaporator is more difficult to visually inspect . You can remove the resistor on the box an take a peak. One of the major problems with retrofit systems is the refrigerant oil used. The original R-12 system used a mineral based oil. Newer 134-A systems use a synthetic PAG oil which is a corrosive. Retrofit systems should only use a synthetic ESTER oil designed specifically for that application. What happens and it happens a lot is the corrosive properties of the PAG oil will take out the evaporator. Be glad it is not a Mercedes, the dashboard R&R is 20 hours. Hopefully you will find the leak maybe at the condenser, a line? At any rate if you are running a PAG oil you may consider a drain and refill, swapping out the accumulator. Sounds like a lot and it is, I wish you luck my friend

I used ester and a rebuilt A6 for the initial R134a conversion, but the rebuilt A6 did not last long before self-destructing. Black granules everywhere when I pulled it all apart. The next time around I switched to a Sanden compressor and had new hoses made to fit. The Sanden compressor specified PAG oil, so that is what I used after I flushed the rest of the system.

Are you saying I could do another complete flush, and then recharge with R134a and ester oil? How critical is it to flush the PAG oil out of the Sanden compressor?

Thank you for the responses. When I replaced the evaporator, I installed the orifice tube, so I know it is there and not damaged. I drove the truck and the air does blow kind of cold in 88-degree Florida weather, especially when it is not at idle. Is there anything else it could possibly be? The air worked great before I replaced the evaporator and orifice tube.

75gmck25 said:

I used ester and a rebuilt A6 for the initial R134a conversion, but the rebuilt A6 did not last long before self-destructing. Black granules everywhere when I pulled it all apart. The next time around I switched to a Sanden compressor and had new hoses made to fit. The Sanden compressor specified PAG oil, so that is what I used after I flushed the rest of the system.

Are you saying I could do another complete flush, and then recharge with R134a and ester oil? How critical is it to flush the PAG oil out of the Sanden compressor?

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Shoote said:

Thank you for the responses. When I replaced the evaporator, I installed the orifice tube, so I know it is there and not damaged. I drove the truck and the air does blow kind of cold in 88-degree Florida weather, especially when it is not at idle. Is there anything else it could possibly be? The air worked great before I replaced the evaporator and orifice tube.

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Black death! You cannot flush a compressor or the accumulator. You can drain and refill, and yes.

Shoote said:

Thank you for the responses. When I replaced the evaporator, I installed the orifice tube, so I know it is there and not damaged. I drove the truck and the air does blow kind of cold in 88-degree Florida weather, especially when it is not at idle. Is there anything else it could possibly be? The air worked great before I replaced the evaporator and orifice tube.

Click to expand...

Pressure = temperature. Feel on both side of the orifice. One side cold, one side hot, low and high pressure. AC 101: does not get cold, takes heat away. You need air going through the condenser, make sure there is no restriction, the fan is working and there is a shroud

75gmck25 said:

so my plan is to add leak detector and then crack open the housing under the hood to check for any evidence of a leak in the evaporator.

Click to expand...

One other way to check the evaporator for leaks is after adding the leak detector, look under the vehicle and find the evaporator condensation drain. Shine your black light there.

75gmck25 said:

Bottom line - the the '75 A/C system seems to be a one-off solution, but replacement parts are available.

Click to expand...

GM used the very cold POA system until 1973. The VIR system, 2 years 1974 and 1975 depending on the vehicle line. Trucks sometimes were second to the car lines.

The fact that you have 50psi on the high and low side with the compressor running means one of two things.

1. Your compressor is no good
2. Your restriction is missing. (Orifice tube)

If you had poor airflow through the condensor you would have very high pressure on the high side.