3800SC A/C Pressures (Page 1/2)
sdgdf AUG 27, 04:39 AM
I have my A/C all setup on my 3800SC '88 coupe and its still a major headache. I'm using a '88 duke V5 compressor, brand new, wired up with the 3-wire pressure sensor under PCM control with the 3800SC pcm. I've also replaced the accumulator and orifice tube. Orifice tube didn't look bad so I don't suspect a nasty evaporator or condenser.

I filled the system with 8oz of PAG 150, 4 in each the compressor and accumulator, and got a good vacuum 30psi with a harbor freight pump. It held overnight so no leaks. I used harbor freight gauges and put in 3 12oz cans of 134, 36oz total. All cans emptied and I purged air out of the line properly when I hooked them up. 85F ambient temp, best I got was about 50-60psi on the low side and 150psi on the high after I filled. At idle it produces 50F or so at the center vent. On max/recirc on med-high fan. Driving I read as low as 40F but if the car stops at all the cooling is just barely enough. I read old threads that say its supposed to drop to 30 on the low and go as 200-250 on the high and I'm supposed to get 40F or less EASILY at the vents, what's going on here? It just sits at 50-60psi on the low even if I rev it to 2500 in the garage.
jelly2m8 AUG 27, 04:45 AM
I don't even know how one can make a stock Fiero Compressor work with the 3800 platform 3 wire pressure switch even work and I am a certified AC technician and have a degree in Electronics engineering along with a Red Seal Automotive technician degree..........

Either remove the 3 wire pressure switch and set it all back to the Fiero wiring with a Fiero Compressor or throw that Fiero compressor junk away and install a 3800 compressor...........

[This message has been edited by jelly2m8 (edited 08-27-2023).]

jelly2m8 AUG 27, 04:50 AM

quote
Originally posted by sdgdf:

I have my A/C all setup on my 3800SC '88 coupe and its still a major headache. I'm using a '88 duke V5 compressor, brand new, wired up with the 3-wire pressure sensor under PCM control with the 3800SC pcm.



You could stop there, that wont work
sdgdf AUG 28, 02:49 PM

quote
Originally posted by jelly2m8:

I don't even know how one can make a stock Fiero Compressor work with the 3800 platform 3 wire pressure switch even work and I am a certified AC technician and have a degree in Electronics engineering along with a Red Seal Automotive technician degree..........

Either remove the 3 wire pressure switch and set it all back to the Fiero wiring with a Fiero Compressor or throw that Fiero compressor junk away and install a 3800 compressor...........




They’re both V5 compressors. Both variable displacement.

I have a problem where the 3800sc compressor only has 3 mounting ears and they line up with only 2 spots on my bracket. And it also doesn’t line up with my ac lines and I’d have to get a new line made. It seems that I have a motor mount that’s using the mounting point where the Grand Prix ac bracket mounts. Whoever did this swap designed it for the V5 that came with the original duke.

My backup plan has been to wire up the ac request through the low and high pressure switches on the back of the fiero v5.
sdgdf AUG 28, 06:49 PM
My friend is an ASE certified mechanic and from what we’ve both come up with it’s simple. Power to ac clutch connector. Correct amount of charge of refrigerant and oil. The compressor is supposed to run and the high and low sides develop different pressures until they hit a limit with the switches which cuts the compressor off. If it’s not building that difference in pressures it’s either a bad compressor or a clog somewhere? It just runs and doesn’t seem to cut off though I don’t understand variable displacement compressors.
sdgdf AUG 29, 04:03 AM
I’ve stumbled upon what could be the answer to my issues. The variable compressor is variable because of a compensation valve: https://www.fiero.nl/forum/...90907-2-091489.html. It changes the stroke of the pistons inside the compressor per vehicle application to keep the evaporator from freezing. No idea what mine has right now I’ll have to check tomorrow, but it could be why my low side pressure is high. If this setup wouldn’t work you’d think I’d have 0 cooling/no compressor engagement.

[This message has been edited by sdgdf (edited 08-29-2023).]

Dennis LaGrua AUG 29, 08:17 AM
When we did 3800 swaps we always used the compressor that came with the engine and used the pressure switch on the high side line for PCM control. Must agree with jelly2m8 that its a better way to go. My 3800SC swap blows ice cold. I just could not justify using a R12 compressor/system on a new engine swap but you say the compressor is new so who knows?
Your pressure readings for R134 are way off. Three full cans of R-134 is also overloading the system .

------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

sdgdf AUG 29, 05:32 PM

quote
Originally posted by Dennis LaGrua:

When we did 3800 swaps we always used the compressor that came with the engine and used the pressure switch on the high side line for PCM control. Must agree with jelly2m8 that its a better way to go. My 3800SC swap blows ice cold. I just could not justify using a R12 compressor/system on a new engine swap but you say the compressor is new so who knows?
Your pressure readings for R134 are way off. Three full cans of R-134 is also overloading the system .




I don't want to purposefully be contrary or an ass, but when I went to fill I searched the forum and found this: https://www.fiero.nl/forum/Forum2/HTML/135787.html

In that thread RWDPLZ corrected someone who said to use only 2 cans.

I'm not sure what to do about putting a 3800SC V5 on, that's what I wanted to do originally and because of the motor mount that's there, I can only fit it with 2 ears hooked up. And I'd have to get a new line made. It sure threw me for a loop when during this project I had assumed the entire time it had a 3800SC compressor down there, but I went to hook things up and it was from a Fiero . I had already gone through and wired it all up as for a 3800SC compressor .

I was thinking of testing it by hot-wiring the compressor clutch to come on. Wire it 12V off the battery with a switch and a fuse to see if the PCM control is causing a problem? A Fiero V5 should blow cold just fine with r134 conversion. If the pressures get too crazy without pressure switches I can just switch it off as I'm testing in the garage.
sdgdf AUG 29, 07:46 PM

quote
Originally posted by sdgdf:

I’ve stumbled upon what could be the answer to my issues. The variable compressor is variable because of a compensation valve: https://www.fiero.nl/forum/...90907-2-091489.html. It changes the stroke of the pistons inside the compressor per vehicle application to keep the evaporator from freezing. No idea what mine has right now I’ll have to check tomorrow, but it could be why my low side pressure is high. If this setup wouldn’t work you’d think I’d have 0 cooling/no compressor engagement.






Mine doesn’t have a color. No idea what it is without contacting RockAuto. So I ordered a green one off eBay and hopefully that fixes things.

[This message has been edited by sdgdf (edited 08-29-2023).]

jelly2m8 SEP 02, 12:33 AM

quote
Originally posted by Dennis LaGrua:

When we did 3800 swaps we always used the compressor that came with the engine and used the pressure switch on the high side line for PCM control. Must agree with jelly2m8 that its a better way to go. My 3800SC swap blows ice cold. I just could not justify using a R12 compressor/system on a new engine swap but you say the compressor is new so who knows?
Your pressure readings for R134 are way off. Three full cans of R-134 is also overloading the system .



Yep mine on R-134 is cold enough I turn it down, I put in the 2.25 LBs that RWDPLZ posted in some tread, It blows plenty cold.

[This message has been edited by jelly2m8 (edited 09-02-2023).]