AC Controllers/Amplifiers

AC Controllers/Amplifiers Offered by MR2 Heaven in collaboration with Messerworks LLC All units are built and tested prior to shipping Replaces the beige or black AC amplifier under your dash that is discontinued and no longer available from Toyota. Which unit does your car need? Toyota fitted three different A/C amplifiers across the SW20 run. They look alike, they are not interchangeable, and between them the terminal numbering changed completely. Five minutes with a torch settles it — and it is the one thing you must get right before you order anything on this page. 1 Find the amplifier and read its label. It is the box the A9 harness plug goes into, behind the center console under the dash. On the label is a Toyota part number beginning 88650-. That number is the answer — not the year, not the engine. 2 No label, or unreadable? Count the wires. Count the populated cavities in the A9 plug. 14 populated is the -17120 family. 16 is the -17130 family. The two extra wires on the later car are a brown BR — the amplifier's own output to the engine ECU — and a brown/white BR-W strap. 3 Use the build date as a cross-check, never as proof. US 1991 is almost always -17120. US 1993–95 is -17130. A US 1992 car has to be read off the label — the changeover happened in December 1991, which falls inside that model year. Any car built from December 1991 onward, in any market, is -17130. 4 Has the engine been swapped? Then you want the Swap Edition — but only if the car started life with a -17120. A swapped car that came with a -17130 should wait for Unit B, whose firmware can switch the extra outputs off. Swap Edition — make sure this is actually your car The Swap Edition is built for one specific situation. Check these four things before you spend anything; if any of them is not you, the lineup has the unit that is. ReplacesAmplifier part number 88650-17120 — the beige unit on early cars. That part number is what the Swap Edition was designed against. A -17130 car needs Unit B. EngineAn engine swap — 2GR-FE or similar. The A/C circuit itself is stock MR2, so what matters isn't which engine, it's that the original engine-management side of the amplifier's job is gone. TransmissionManual. Automatics used an extra amplifier terminal that isn't part of this build — a stock automatic is covered by Unit A. ECU signalYour swap ECU takes its A/C input as +12 V from the same wire that engages the clutch. That's the factory B-W signal path, and it's how this controller hands your ECU the idle-up request. If your ECU expects a ground instead, talk to me before ordering. Then confirm the amplifier is really the fault This takes ten minutes and tells you whether you need this part or something cheaper. 1 Your refrigerant charge is good. A low system won't engage the clutch no matter what controls it — the factory pressure switch cuts it off. Check the charge first. 2 Grounding the L-O wire engages the clutch. At the amplifier plug, jump the blue/orange wire to ground with the engine running. If the compressor kicks in and you get cold air, your compressor, clutch, relay, and refrigerant are all fine — the amplifier is the failure. 3 Your A/C button does nothing. 12 V shows up on the pink wire when you press it, but the clutch never engages. That's the amplifier failing to close the loop. If grounding L-O does nothing, stop. Your problem is upstream — relay, fuse, pressure switch, compressor, or charge — and this controller will not fix it. The full diagnostic checklist ships with every order, and if you're not sure what you're seeing, email me before you buy and I'll talk it through with you. What it actually does The factory amplifier had five jobs. This reproduces all five, from the same wires, at the same plug. Clutch control A logic-level MOSFET grounds L-O to energize the A15 clutch relay — exactly what the OEM unit did, with no mechanical contacts to burn. Freeze protection Reads your factory evaporator thermistor and cycles the compressor with proper hysteresis plus minimum on/off timing. No short-cycling, no iced core. Engine-run detection Senses alternator charging voltage with hysteresis and a dip-grace timer, so the compressor's own engagement sag doesn't drop it out. Key-on with the engine off does nothing, same as stock. Radiator fans, both stages An on-board relay sources 12 V to the fan enable circuit, and a second output holds the motors in series for LOW — releasing to parallel HIGH above ~90 °C. The factory behavior most replacements skip entirely. Pressure safety left in hardware Your A13 dual pressure switch still gates the relay's power feed. High or low refrigerant pressure cuts the compressor whatever the software thinks. That circuit is untouched. Idle-up signal The B-W wire — 12 V only while the clutch relay is closed — is the factory signal path to the ECU's A/C input. Tap it and your ECU raises idle under compressor load. Why swapped cars first When you swap an engine into an SW20, the A/C amplifier loses half its job. The vacuum idle-up actuator it used to drive is gone with the old engine, and the igniter signal it watched for the high-RPM cutout belongs to an ignition system that isn't in the car anymore. A swap ECU handles those itself. It just needs to be told the compressor is engaging — and it wants that as +12 V on the same wire that closes the clutch relay. So the controller's job gets simpler and cleaner, and everything left is A/C circuitry that's still pure MR2. Tape off the vacuum idle-up wire. There's no actuator on the other end of it anymore. Tap B-W to your swap ECU's A/C input. It goes +12 V only while the clutch relay is closed, so your ECU raises idle exactly when the compressor loads the engine. Everything else stays factory. Same plug, same sensors, same relays, same pressure switch. This is the configuration it was built and driven on — a 1991 SW20 with a 2GR-FE and a manual gearbox. Not a design on paper waiting for a first customer to find the problems. Board, enclosure, and hardware. The whole assembly is 90 × 70 mm. The housing is printed in ASA — not PLA — so it holds its shape through a closed-up summer behind the dash and won't go brittle in UV. Designed against the factory manual, not guesswork Every terminal on the board was audited against the 1991 electrical wiring diagrams — page by page, wire by wire. Copper-verified The routed 2-layer PCB was checked net-by-net against the netlist before a single board was ordered. Fails safe Boots with the clutch off. Loss of signal drops the compressor rather than latching it on. Reverse-polarity Schottky and a TVS sit at the supply input. The traps are documented Identify the thermistor pair by measuring ~1.1 kΩ, never by pin number. The 12 V feed is R-L off the GAUGE fuse — not L-R, a different wire in the same loom. The W3 switch is a fan switch, not an overheat cutout, and is deliberately unused. These are the mistakes that cost me time; they're written down so they don't cost you any. 43 wires, each numbered The wiring guide is plain English, in order, with a full J1 position map. No schematic literacy required. The complete schematic — included with every order, at every tier. One screw terminal (12 to 15 positions, by unit). Every wire lands in a labeled position — no connectors to crimp. Sealed printed enclosure with ziptie tabs — mounts where the old amplifier lived, or anywhere dry behind the dash.