PFF - Pennock's Fiero Forum, PDA Edition

Adding AC to 88 with 4.9 Convertion (Page 1/1)

deanearl

JUL 18, 10:57 PM

A few years ago I performed the 4.9 conversion on my 88. At the time I had the 2.5 AC hoses modified to fit to the 4.9 AC compressor and got them hooked up. I've drug my feet for 3 summers now and want to get the high and low pressure sensors added, wired in so I can charge and use my system. Anyone have pictures and information on what they used, how they did the wiring and addition of the switches along with first time charging of the system?

Thanks in advance.

Dennis LaGrua

JUL 19, 01:34 PM

The high pressure sensor must be installed on the high pressure line. It is basically a cut off switch to keep line pressures under control. It is wired in series with the A/C clutch circuit where exceeding high pressures will momentarily de-energize the clutch. I have not done the 4.9L A/C setup yet as I am trying to figure out what A/C high pressure sensor to use. Maybe someone else can answer this question. Good that you used the Cadillac compressor as it has a higher capacity than the Fiero unit and should provide great cooling. .

------------------
" 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 "

Raydar

JUL 19, 03:07 PM

I ordered the Fiero High Pressure switch.
If you have a replacement compressor, there is a dummy plug in the back of the compressor, that can be removed and replaced with the switch. (Switch can go in either hole.)
If you have the factory 4.9 compressor, it likely does not have the holes for the switches, and it will have to be installed in the high side line, as Dennis said.

Edit - Can anyone think of a reason that it could not be installed on the high side fitting in the front compartment, and wired in series with the pressure cycling switch?

Dennis LaGrua

JUL 19, 10:15 PM

quote

Originally posted by Raydar:

I ordered the Fiero High Pressure switch.
If you have a replacement compressor, there is a dummy plug in the back of the compressor, that can be removed and replaced with the switch. (Switch can go in either hole.)
If you have the factory 4.9 compressor, it likely does not have the holes for the switches, and it will have to be installed in the high side line, as Dennis said.

Edit - Can anyone think of a reason that it could not be installed on the high side fitting in the front compartment, and wired in series with the pressure cycling switch?

High pressure A/C switches may bot be available in the thread size for the original R-12 HP port.

deanearl

JUL 23, 11:31 PM

i looked and mine must be an original compressor as it does not have any ports for the high pressure switch to connect into. Now will need to figure out the connector and high pressure switch which can be adapted to the high pressure line up front. Any way one can be added to the test port on the high pressure line?

Dennis LaGrua

JUL 26, 05:07 PM

I would think that the easiest solution would be to adapt one of the later GM high pressure binary A/C switches that GM used. To use this switch you must find a suitable switch port nipple and aluminum braze it on to the manifold connection near the firewall or find a T fitting switch port for which the high side hoses can be crimped onto. Still not sure that an adaptable high pressure binary switch is available that will screw on to a suitable port fitting. Most of the ones that I have looked at have external threads.

Will

JUL 26, 06:37 PM

I guess the 4.9 ECU never had an input for an A/C pressure transducer?

Many GM cars starting with Caddies in the '90's switched over to using an A/C pressure transducer instead of the array of switches the Fiero system uses. In the Northstar cars, this transducer was read by the HVAC module, which is part of the instrument panel. Later GM moved that function over to the ECU.

Dennis LaGrua

JUL 27, 06:01 PM

quote

Originally posted by Will:

I guess the 4.9 ECU never had an input for an A/C pressure transducer?

Many GM cars starting with Caddies in the '90's switched over to using an A/C pressure transducer instead of the array of switches the Fiero system uses. In the Northstar cars, this transducer was read by the HVAC module, which is part of the instrument panel. Later GM moved that function over to the ECU.

The 4.9L A/C system is not under ECM control. It uses a simple series circuit on/off control of the A/C compressor just like the Fiero, except that the Cadillac compressor does not have the high pressure switch on it like the Fiero until does. The easiest solution is to splice in an inline T w 10mm switch port to the #8 high side hose and use one of the many high pressure screw on binary switches available
inline 10mm splicer for std barrier hose.
UPDATE: Use the above T fitting on the high side line, with Four Seasons #36678 High pressure switch ( will fit 10mm) and four seasons 37240 connector. Put in series with the compressor clutch circuit and you are protected.

------------------
" 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 "

[This message has been edited by Dennis LaGrua (edited 07-29-2019).]