Odd restriction problem...need another perspective

[jim14410]

Wow, I feel lucky to have found this forum. I have posted this question in a few vehicle specific automotive forums but get the general armchair responses...

So I am working with a 93 Buick Lesabre. Originally charged with r12 was converted at a GM dealership to R134a back in 2013. Not exactly sure what they did or didn't do, but the sticker shows they changed the oil and recharged with 2LB of r134a (original r12 charge was 2.4Lb). Orig compressor, condenser and I assume evap. Honestly can't tell on the accumulator unit whether it was changed or not, or orifice tube. I didnt own the car when this took place.

Anyway - here we are in summer. I noticed it was cycling a lot so I lazily threw a can of gas in it and charged it until the accumulator was cold and sweating...yes not very fancy but I was in a hurry. After that I was still getting temperature swings from the vents (comp cycling) and noticed more drag on the engine when it kicked in. Ok, fine... more work.

I pulled out the gauge set and vacuum pump, pulled a vacuum for a good 30 minutes and then let it sit in vacuum for 2 hours. No movement on the gauges. Added 3 12oz cans of r134a completely. Figure with loss from bleeding the hoses, I'm right around 32-34 oz charge...so very close to the 2lbs. I've read that you only want about 80% of your original r12 factory charge, so I'm on the money.

Pressure readings are good, if I kick the RPM up a little above idle and let it stabilize, I get around 35PSI low side and about 235 high side. A/c on max recirculate, 90-95 degrees outside ambient. The suction lines are cold and sweating. If I rev the engine more, pressures will slowly drop on the low side into the upper 20s and begin to frost the lines - then of course it cycles out on low pressure and we begin again.

Problem begins here: Inside vent temps dont' drop below 50 degrees. Even when the low side pressure is around 30PSI and the line running to the compressor is so cold it hurts your hand. So I did some more digging...

Here is the system layout: The orifice tube is located at the condenser outlet, so then low pressure refrigerant travels along the fender from the front of the car to the evaporator, then out of the evaporator, into the accumulator, then back to the compressor. It seems weird to me that it is not closer to the evap but I'm not the engineer, just the sweaty guy trying to fix it.

So following the above path, the temperature of the refrigerant lines after the orifice tube feels about 50deg, going into the evaporator feels about 50 deg (by the palm of my hand feel anyway) The accumulator feels slightly colder than the line leading into the evap (odd since this is on the outlet side). The low side pressure port where my gauge connects is after the accumulator on the line leading back to the compressor. The line leading out of the accumulator will frost when system pressures drop into the 20s, it is so cold it hurts. During this time, the line leading into the evaporator and the accumulator body itself will be cold, but nowhere near this cold..I would suspect they are in the mid 40's which is giving me the 50degree vent temps on high blower. Running down the highway on cool mornings, the compressor cycles so much it never really gets much cooler than ambient. It actually runs longer / better when it is hot out.

So to me this sounds like I must have a secondary restriction. I've asked around and most people say that accumulators wont clog, but it seems like this is the most likely case. I'm here partially because typing out this fiasco helps me think, and hopefully some technical perspective from another user could see something I missed...it was hot outside after all.

I'm not one to throw parts at a problem, so anything I can do to more accurately test and identify the problem would be much appreciated.

[GM Tech]

How's your airflow inside the car from the vents? A 93 H-car was notorious for evaporator leaks where the oil leached out onto the air inlet face of evap and then dirt and debris would plug up the air flow path, causing huge inefficiencies, as well as a loss of refrigerant. I personally changed dozens from about 89 model year to end of 93 model year. Problem was fixed in April of 1994 as I recall- It was caused by acid rain reacting to improper heat treating of evaporator cores- (hang time in the processinog oven) - anyway, if your evap is the original (you can tell if it has been changed by looking at cut marks in rubber insulation panel behind accumulator) you need to pull out the blower resistor (if manual system) or blower motor control module (if deluxe climate control digital readout system) and peek at the face of evap with a flashlight- see if there is oil/greasy build-up- if so, it needs changed. To pull resistor, it is easiest to remove relay center (or just pull it out of the way).

The air flow inside should blow your hair off your forehead when you are 6 inches away from vents.....

[ice-n-tropics]

HI GM Tech
Yours is nominated for post of the month! Pretty good advice to look through the resistor mounting opening.
Reminds me of the air flow problem in a pick up I fixed. Turns out the dove hunter/owner threw his doves on the passenger floorboard and the dove feathers were sucked into the evaporator inlet until entering air side of the evaporator was totally blocked.
hotrodac