1970s 1975 Eldorado AC problems

[_Cap_]

   So I've been struggling with my AC system in my 1975 eldo for a long time now, which has been converted to use R-134a.  I've replaced the drier, the expansion valve, compressor and pressure switch for the compressor (the system didn't work before at all).  However, even after I top off my ac with Freon, the ac only works temporarily.  At first for like a week but recently its been to the point were once the car gets warm, so after about 15 miles of driving, the ac completely stops and just blows ambient air.  Once the car sits for a bit it will go back to working, but then shuts off.
   I seem to also have a growing AC leak, but i cant find any of the leak detection (red dye).  I have a feeling I have a leak in my evaporator core, but I don't see how a leak could be causing it to turn on and off as it does.  I'm 17 so taking it to an ac shop is last on the list for financial reasons, and its my daily in Florida so it's at the top of my priorities.
  If anyone has info about this problem or similar issues on these systems it would be greatly appreciated

[TJ Hopland]

Can you post some underhood pics of the AC plumbing?  What you are describing doesn't sound like a stock 75 and you say its 134 so we know at least some changes have happened.   It would be helpful to know if its stock or what has or hasn't been changed. 

The evaporators leaking were not a common issue in this era but anything is possible.  Checking the condensate drain tube is usually where you can see dye if its a major leak.   I don't recall the 75 layout but sometimes pulling the blower will give you a view or at least a place to stick a bore scope or mirror to try and see part of the evaporator. 

Does the control system seem to be working properly?   If you are in auto and turn the temp dial slowly and pausing for it to do its thing does it change the fan speed and which vents the air is coming out?   Do you hear a lot of clicking down under the dash?   A stock 75 the compressor should be running all the time except off and econ/vent mode so you may have control issues as well as mechanical refrigeration issues. 

[_Cap_]

All of the ac systems seem to work fine, auto adjusts the fan speed well and when the ac is working the car holds the set temp, or what feels like the set temp, never took a proper gauge to it. But the controller seems to work as intended, checks off all the boxes of what it should do from the shop manual.
   And yeah its not entirely stock, I have a VIR eliminator kit on it to run R134.

https://www.camarocentral.com/74_76_Camaro_Air_Conditioning_A_C_VIR_Eliminator_p/HTR-124.htm?srsltid=AfmBOoovmQE2NOcUU6RaPyK-Oj9MBElK_KFwxrbO-Ub28wXm_Q0HqdCRs7E

["Cadillac Kid" Greg Surfas 15364]

Okay, a bit to unwrap here. From the pictures you have replaced the VIR system, and it looks like a compressor cycling sensor based on evaporator pressure. If you are short of refrigerant which your admitted leak will result in, and since you have eliminated the back pressure control the VIR contains, initially the suction pressure will be low, resulting in an iced coil and reduced air flow and then as the pressure goes even lower, the compressor cycles off.  With an iced coil it will take a while for the pressure to build up to the point where the compressor will be switched on.
First step is to find the leak using an electronic leak detector, fix it and recharge the system. I believe some of your issues will then be solved.
Once you have done that be aware tht I can count the instance on the fingers of one hand where an A-6 compressor operating on R-134a has provided sufficient cooling for summertime driving in city traffic.
Greg Surfas

[_Cap_]

yeah, i got the car with the system and R-12 isn't the easiest thing to get your hands on from what I can tell.
but thanks, ill take the cover section of my evaporator core today and see if there is any evidence of a leak.
When the system works it blows out cold enough air, nothing ground breaking but comfortable. Ill check it, don't have an electronic system to check it, and correct me if I'm wrong but i don't think you can use those systems on R134a systems? at least that's what i was told by a few older mechanics

["Cadillac Kid" Greg Surfas 15364]

Morgan,
in order to pull the cover on your evaporator, you have to disconnect the refrigerant lines or cut the case.  Where you are (FL) you are going to need all the capacity your system can put out, and with R-134a you are down over 20%. Will R-134a work? Yes. Will it provide anything near a stock R-12 system? Not likely. If you can't afford an in expensive electronic leak detector, try the soap bubble type leak detection fluid.  As TJ says, leaks in the evaporator in this era of system are VERY rare.
Greg Surfas

[_Cap_]

yeah i know the system is very limited buy it, if i could change it i would. I've been told by a few people leaks in the evaporator core is extremally rare, but the casing around it has been opened before by someone, and if it isn't a leak there, id expect to see the red leak detection else ware on the system but there isn't any, I will check it with some soapy water though, and make sure of it, especially around the condenser, if i cant find anything then ill pull off part of the cover for the evaporator core, or at the very least stick a camera in there from the blower motor port.

[_Cap_]

So with a bunch of head scratching, soapy water and a bit of dumb luck, found out the issue is in my compressor low pressure switch.  There was a leak around it, probably due to an improper seal, which i think was causing a low pressure zone around it, triggering the switch and leaking freon.  And there is a loose connection inside the switch, if I wiggled the connection points on the switch it would turn on and off the compressor causing it to turn off and on randomly.

["Cadillac Kid" Greg Surfas 15364]

When you get around to recharging the system be sure and add a few ounces of oil
Greg Surfas