The compressor clutch relay on this model connects through a 20-amp fuse at position 18 in the under-dash fuse box. Locate the green/white wire running from the climate control switch to terminal A5 of the heater control amplifier. A break here often mimics refrigerant leaks due to intermittent engagement. Verify continuity with a multimeter before assuming mechanical failure.
Condenser fan operation depends on two separate circuits. The high-speed fan engages when engine coolant reaches 106°C via the engine control module’s pink/black wire to the A/C pressure switch. Low-speed fan cycles continuously when ambient temperatures exceed 27°C, triggered by a dedicated purple/white wire to the fan control relay. Check for voltage at both relay sockets during failure symptoms–corrosion here causes erratic cooling performance.
Blower motor resistors for speeds 1-3 cluster behind the glovebox. The fourth speed bypasses these resistors entirely, relying on a direct blue wire to the blower motor switch. If intermediate speeds fail but the highest setting works, replace the resistor block. For full failure across all speeds, trace the grey/black ground wire from the blower’s case to chassis ground–poor grounding is a common but overlooked issue.
The A/C pressure switch cuts compressor engagement at 30 psi and above 300 psi. A faulty switch can stall cooling entirely or cause clutch cycling every 2-3 seconds. Test with a manifold gauge set: if pressures are within normal range (28–290 psi) but the compressor cuts out, replace the switch. The wiring harness to the switch includes a critical brown/yellow wire–damage here disrupts both cooling and fan operation.
Passenger cabin temperature sensors feed data to the amplifier via a grey/red wire. A disconnected or damaged sensor defaults the system to 100% recirculation, reducing efficiency. Remove the lower dash panel to access the connector–clean contacts with electronic cleaner before assuming sensor failure. False readings here often trigger erratic blower behavior and improper temperature calibration.
Understanding the Climate Control Electrical Layout for a 2000-Era Compact Sedan
Locate the fuse labeled “A/C” under the dashboard panel–typically marked as #13 (10A) in the under-dash fuse box. If the blower motor runs but cold air isn’t produced, this fuse is the first checkpoint. Replace it with an identical amperage rating only after confirming no short circuits downstream with a multimeter reading below 0.5 ohms.
Trace the yellow/red striped wire from the A/C pressure switch mounted on the receiver-dryer. This conductor carries the critical signal to the clutch relay when refrigerant pressure exceeds 45 psi. Interruption here is a common failure point; probe both terminals of the switch while cycling the system to verify continuity at the appropriate pressure threshold.
The compressor engagement circuit relies on three parallel paths:
- Blower motor resistor – ensure the white/blue wire maintains 12V when the fan is set to any speed above “Low.” A drop below 10.5V indicates corrosion at the connector;
- A/C relay coil – the light green/black wire must transition from 0V to 12V when the climate control unit sends the engagement signal;
- Clutch coil – the dark blue/white wire should measure 12V at the compressor terminal only when the relay clicks and system pressures align.
Inspect the condenser fan operation independently. The fan motor receives power via the black/yellow wire through a dedicated 30A fuse (#32) and activates at 215°F or when A/C pressures surpass 200 psi. Bypass the thermal switch temporarily to isolate whether overheating stems from electrical failure or a heat exchange bottleneck.
Ground connections merit equal scrutiny. The main ground distribution point, identified by a thick black wire cluster near the firewall mounting bolt, must show ≤0.2 ohms to chassis. Loose or oxidized terminals here manifest as intermittent cooling drops or erratic idler pulley movement–both upstream symptoms that lead technicians to misdiagnose compressor failure.
For voltage stabilization, integrate a 1000μF 25V capacitor across the clutch relay coil terminals. This modification filters transient voltage spikes characteristic of aged alternators that frequently damage clutch engagement circuits. Install bypass diodes rated 1N4007 across any inductive loads (e.g., condenser fan) to prevent back EMF from propagating through shared harnesses.
Replace the two-temperature sensor if cabin temperature readings fluctuate unreasonably. The sensor–mounted beneath the dash on the passenger side–uses a thermistor with resistance decreasing as temperature rises. At 77°F, expect ~3.5 kΩ; at 50°F, ~6.0 kΩ. Deviations beyond ±15% necessitate sensor substitution to restore precise climate control modulation.
When refrigerant levels are verified but cooling remains subpar, interrogate the expansion valve orifice size. Stock orifice diameter of 1.5 mm often becomes restricted after long-term oil breakdown. Swap to a 1.8 mm orifice under high ambient conditions (≥90°F) to enhance evaporator saturation efficiency. Verify post-adjustment superheat readings between 8°F and 12°F for optimal performance.
Finding the Climate Control Relay in the 2000-Model Compact Sedan Fuse Panel
Start under the dashboard on the driver’s side, directly above the pedal assembly. The fuse box cover holds a map on its underside–remove it by pressing the two tabs at the top corners. The relay you need sits in slot 11 on the left row, labeled A/C COMP or CLUTCH in the diagram. If the label is missing, count from the bottom: it’s the third relay in the vertical stack. Use a flashlight to confirm the part number–39794-SR3-A11–printed on the relay’s plastic case.
If the relay isn’t in slot 11, check slot 9 adjacent to the IG1 fuse; some builds swap positions with the RADIO relay. A quick multimeter test verifies function: probe the large pins while cycling the ignition. A live relay will show 12V at one pin and a switched ground at the other when the climate selector is turned to A/C. No voltage? Move to the under-hood fuse block–access it by popping the latch near the windshield washer fluid cap. The secondary relay sits in slot 6, often marked COMP.
Relay and Fuse Locations Summary
| Location | Slot | Label | Part Number |
|---|---|---|---|
| Driver’s dash fuse box | 11 | A/C COMP / CLUTCH | 39794-SR3-A11 |
| Driver’s dash fuse box (alternate) | 9 | Unmarked or RADIO | 39794-SR3-A11 |
| Under-hood fuse block | 6 | COMP | 39794-SR3-A01 |
Swap a known-good relay from the same fuse box–HORN or ECU relays have identical pin layouts. If the compressor engages, the original relay is faulty. Pull it straight out using needle-nose pliers; wiggling can damage the socket. Clean the socket contacts with a wire brush if corrosion is visible–common in humid climates. Reinstall the relay by pressing firmly until it clicks. If the system still doesn’t respond, trace the light blue/red wire from the relay to the compressor–check for continuity at the pressure switch connector mounted on the accumulator.
The under-hood relay handles high-current demands during initial engagement. If it fails, the clutch won’t pull in, though the dashboard controls may remain live. Test the green/white and black/yellow wires at the relay connector–both should show 12V with the ignition on. A missing ground on the black/yellow wire points to a bad ground, typically located at G301, a bolt behind the left headlight. Remove the bolt, sand the contact patch, and reattach with dielectric grease. If voltage checks out but the compressor stays silent, jump the relay terminals momentarily–if the clutch engages, replace the relay.
Factory service manuals outline a connector voltage test for slot 11: disconnect the relay, then backprobe slots A (green/white) and B (black/yellow) with the ignition on and A/C set to MAX. Both should read 12V; slot C (light blue/red) should drop to 1.5V when the compressor cycles. If readings deviate, suspect a faulty A/C pressure switch or ECM signal. The switch, bolted to the accumulator, often fails silently–replace it if system pressures check out but the relay gets no ground signal.
Step-by-Step Guide to Testing the AC Pressure Switch Electrical Connections
Locate the pressure sensor near the refrigerant lines–typically mounted on the accumulator or condenser. Disconnect the electrical harness by pressing the release tab and gently pulling the connector apart. Inspect the terminals for corrosion, bent pins, or debris; clean with a small wire brush or electrical contact cleaner if necessary.
Set a digital multimeter to the 20V DC range. Insert the black probe into the ground terminal of the vehicle’s battery or a known chassis ground. Touch the red probe to the signal wire in the connector (usually the smaller gauge wire, often blue or purple). With the engine off but ignition in the ON position, the reading should match battery voltage (±0.5V). A deviation indicates a broken circuit or faulty relay.
Reconnect the harness temporarily. Start the engine and activate the climate control system to maximum cooling. Recheck voltage at the same wire; it should drop below 1V when the compressor engages, confirming the switch’s activation. If voltage remains unchanged, the sensor may be stuck open or the control module failing to send a ground signal.
Probe the ground wire (typically black) at the connector while the system is running. The multimeter should read near 0 ohms, verifying a solid ground path. High resistance (above 0.5 ohms) suggests a corroded connection at the chassis ground point–trace the wire to its termination and clean the mounting surface.
For a dual-pressure switch (low/high side), test both circuits separately. The high-side switch should open at ~450 psi (no voltage drop), while the low-side should open below ~25 psi (voltage returns). Use a refrigerant pressure gauge set to verify actual pressures against switch behavior. Discrepancies indicate a faulty switch requiring replacement.
If all readings align but the compressor fails to engage, backprobe the climate control module’s output pin assigned to the pressure switch. Measure for a pulsed ground signal (0-5V toggling) while cycling the AC button. Absence of this signal confirms a module fault or lost communication with the body control unit.
Reassemble all connectors once testing completes. Clear any stored trouble codes with an OBD-II scanner before retesting. Replace damaged wiring with automotive-grade 18-gauge wire, soldering joints and sealing with heat-shrink tubing to prevent moisture ingress.