I have another thread about AC diagnostics and my new to me 88GT. After utilizing some suggestions I’ve determined my system is in need of an upgrade. I’ve ordered the compressor, accumulator, oriface tube, o rings, flush, etc and been doing a lot of reading on the forum.
One recommendation I came across was replacing the AC compressor control valve(s) like pictured here.
First of all, what’s the purpose of the new valve? Can I swap mine from my old compressor or is the new one needed for 134a?
Also, it looks like I have 2 control valves on my old compressor. Do I need 2 new ones?
Finally, how much oil should I add to the system and how much r134a should it take?
R134a operates at different pressure than R12. Did you match up compressors or just go off of parts lists? The one that takes the valve is typically on the 2.5l
That valve is only used on the Variable compressor, as mentioned. If you bought a new compressor, it will have a new valve anyway. No need to buy.
R134 is usually charged at about 80% by weight compared to the stock R12 values. I no longer have my Fiero books, but hopefully someone else will chime in.
Total oil in the system should be about 6-8 OZ. You will have residual oil in the condenser if not replacing that item, so I usually add 2-3 of ounces in the accumulator, and another 2-3 ounces in the compressor. Use Ester oil, as it is compatible with the old mineral oil as well as the R134a. I like to use the oil with Dye, to help find future leaks. Once the compressor is installed, you need to rotate by hand the center part of the clutch 4-6 revolutions, so you can distribute the liquid oil in the compressor into the lines a bit so you don't wind up hurting the compressor on first start.
------------------ '87 GT , '00 3800 Series II SC, 4t65e, Vue Power Steering. (SOLD)
Originally posted by skywurz: I just bought one in Aug and it explicitly said comes with R12 valve. So i had to buy the r134a one as well. Edit: It also came pre-charged with PAG oil and PAG is incompatible with the R12 oil.
Not saying that it is a good idea but when I did my 3800SC swap we used the V7 Compressor. We didn't dump it out of the PAG oil and just blew out the system with air, replaced the accumulator , orifice tube, a few O rings, sealed it up, evacuated, added the 6 oz Ester oil and recharged. Seven years later the system still blows very cold and works well. My theory is that the compressor doesn't contain much oil and the small amount of PAG oil left in it wasn't harmful.
------------------ " 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 "
Not saying that it is a good idea but when I did my 3800SC swap we used the V7 Compressor. We didn't dump it out of the PAG oil and just blew out the system with air, replaced the accumulator , orifice tube, a few O rings, sealed it up, evacuated, added the 6 oz Ester oil and recharged. Seven years later the system still blows very cold and works well. My theory is that the compressor doesn't contain much oil and the small amount of PAG oil left in it wasn't harmful.
Yeah I left the PAG added more PAG but i ran flush through the Evaporator and Accumulator until there was no more visible oil.
I also did not use the $$ Flush i used denatured alcohol. I was shocked how much oil was still in the Evap. my system had been open to air for 13+ years
[This message has been edited by skywurz (edited 01-04-2021).]
If you have an 88 GT, your car doesn't have that control valve, the control valve is only used in the V5 compressors on 86-88 4 cylinder cars. The 88 GT has an HR6 compressor. The HR6 compressor is controlled by the pressure switch mounted on the accumulator, for R-134A, it should be adjusted from 25 psi (R-12) to 21 psi (R-134A) or buying a pre-calibrated new switch.
The two things in the back of your current compressor are not valves, but switches. The old ones can be re-used if they come out intact, but the plastic is usually old and brittle. New ones are available, requiring updated connectors
Car should still take 8oz of oil, but R-134A amount should be 80-90% of the original R-12 charge of 2.5lbs, which would be approximately 2.1 lbs (or 3 of the small 12oz cans).
A small amount of mineral oil remaining in the system is fine, you just want to remove as much as possible. Most of it is going to be in the accumulator and old compressor, with some in the condenser and under-car lines.
Awesome guys, thanks! The knowledge on this forum is invaluable. The switches on the back of my old compressor came out nicely and are in good shape, plastic and all. I also just picked up the correct clutch cycle switch to hopefully complete the parts order.
The rest of the parts arrived today and I have a couple more follow up questions.
On the back of my old compressor right in the center, there is something attached where on the new compressor there is a recessed brass bolt with a Torx grub screw in the middle. What are those and do I need to transfer that as well?
Also, new compressor came with 4 metal / rubber gasket deals. I assume they’re used to couple the ac lines to the compressor. How do I determine which 2 to use?
Yeah I left the PAG added more PAG but i ran flush through the Evaporator and Accumulator until there was no more visible oil.
I also did not use the $$ Flush i used denatured alcohol. I was shocked how much oil was still in the Evap. my system had been open to air for 13+ years
The accumulator contains a sack of desiccant that is used to catch any residual moisture that is left in the system. By flushing it out with solvent you may have defeated its purpose. Standard procedure, is to replace that part if the system is opened. As for flushing the condenser and evaporator that is a good idea.
------------------ " 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 "
The accumulator contains a sack of desiccant that is used to catch any residual moisture that is left in the system. By flushing it out with solvent you may have defeated its purpose. Standard procedure, is to replace that part if the system is opened. As for flushing the condenser and evaporator that is a good idea.
Ha! Yes replace the accumulator. Its cheap. I meant to say condenser in my post not accumulator.
Hey guys, update on my conversion. All went well, by well I mean a few bloody knuckles and choice words, but I got it done. Thanks for all the advice and direction. I probably won’t need it for a while but it was nice working on it in a 65 degree garage now vs a 100 degree garage come summer.
Yessir. 👍🏻 All charged up and ready for summer. On a side note, while charging the ac my radiator fan didn’t come on. That lead me down another trouble shooting rabbit hole / thread and solved that problem. Dirty, burned contacts on the relay. These Fiero’s sure are a lot of fun in the garage! Actually, I enjoy working on it. Especially with the wealth of knowledge on this forum.
