John Bzdel's LS1/T56 Monte Carlo SS

John Bzdel's

1988 Monte Carlo SS

LS1/T56 Change-over page

September 2001 Project Updates

09/04/01 Air Conditioning works after lots of effort!

Unfortunately none of the A/C compressor end hoses that I obtained from a local wrecking yard would properly fit-up to the LT1 R134A revised compressor rear fittings due to a slight offset on the high pressure side of the fitting connection. This view compares the LS1/LT1 type rear compressor fitting (red arrow points to offset) on the left versus the stock G-body fitting on the right. This meant plan "B", have a hose set fabricated to fit using the proper LT1 compressor end with new mating hose ends to match up with my existing connections at the accumulator and condenser.

I forgot to snap a pic of the stock LT1 compressor lines, however, once I determined the correct hose lengths based on where they would be routed this view shows the new hoses with the correct ends installed.
I also had to slightly "massage" the low pressure aluminum line (the large hose) where it bends upward at the front of the compressor. Nominally, it points up 90 degrees at about the 12 o'clock position so I gently twisted it counterclockwise toward the passenger fender to almost a 9 o'clock position. This was necessary to clear the high pressure line attaching from the condenser.
I needed to add a special port on the high pressure line to use the LS1 PCM specific high pressure sensor. Location options were severely limited due to the very short length of the F-body wire harness for this. I also had an R134a evacuation fitting added to the high pressure side in the same location as the OEM R12 fitting. This view shows both fittings in their respective positions next to the accumulator.
This view shows the installed hose routing at the front of the compressor as the low pressure line routes over the PCM to the accumulator. I installed a new accumulator while I was at it to ensure that the desiccant could still absorb any moisture trapped in the system prior to charging.
I also replaced the stock high pressure line orifice with a special unit designed for colder air operation since my new lines were substantially shorter than the OEM set-up and thus they wouldn't hold as much refrigerant.
I only realized that after carefully studying the LS1 PCM wiring schematics for the F-body A/C system that I was going to have to tap into the PCM wire harness and wire in:
- an A/C 12V request signal (light green wire) from my A/C-Heater control to pin 17 on red harness connector
- a 12V relay ground which will activate the compressor clutch when the high pressure sensor detects low system pressure to pin 43 on the red harness connector
- a compressor clutch status wire to pin 18 on the red harness connector which splices into the 12V + lead going to the compressor clutch from the relay

I also had to provide a ground wire to the compressor clutch 2 pin wire harness connector. This was a lot more work than I had originally figured! Oh well!

I bought a 30 AMP Bosch relay and wired it with an ignition "on" hot lead to two sides, connected the PCM pin 43 lead and then the other switched 12V+ side to the compressor clutch harness. I mounted the relay next to the battery on the inner fender so that the OEM F-body two wire harness could reach the compressor clutch.
The final step was installing the new 100" long 6 rib serpentine belt.
I took the car to a local automotive shop to have the A/C system properly charged since I couldn't locate a vacuum pump to properly evacuate the moisture from the system myself. The air now blows icy cold!!!

09/10/01 Tach & speedo now read correctly!

I took my car to Tacoma Speedometer and had Mark (one of the owners) work a little magic with my slow reading tachometer and non-functional speedo.

An Electronic Ratio Adapter by Abbott Enterprises, Inc. was installed with a simple 12V+ ignition hot lead, ground and splicing in the tach lead from the LS1 PCM into the Adapter and then routing the signal out to my tach. By using the 16 dip switches on the unit Mark found the right calibration to make my tach finally read correctly! Another LS1 PCM Achilles heel for retrofit resolved!
The speedo required another specialty item manufactured by Abbott, this time a unit capable of converting an electronic Vehicle Speed Sensor (VSS) signal generated through the PCM and driving the Monte Carlo mechanical speedo cable. This unit is called the Cable X. Once installed with a 12V+ ignition hot lead, ground, and PCM VSS wire, it was just a matter of making a custom cable length to connect onto my existing speedo cable end and setting the dip switches. My speedo is now calibrated to read within less than a 0.006% error at 60 MPH! Pretty cool and so much for having to machine the T56 tailhousing!

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