Putting a long description in here to maybe help others and get some advice.

If you don't want to read the details below here is a summary. My a/c remained on at all times and caused the compressor to overheat. The thermal detector melted, but the a/c remained on. The compressor relief plug opened and all the r-134A is gone. Need to replace the compressor. Trying to figure out why the a/c + fans remain on at all times even with the a/c turned off on the HVAC and no R-134a.

And the details...

A/C went out in 95 °F Houston heat. The a/c compressor clutch was engaged and the radiator fans working while the engine is running. Shut off engine and did a quick pressure test by pushing on the low pressure schrader valve and NO R-134a. Tried to pull a vacuum and the system will not hold vacuum.

Thought low R-134a would stop the compressor from running via pressure switch, so tried turning on/off the a/c with the engine running and the compressor and fans remained on. Wiring diagram shows fans + compressor are controlled by the PCM. The PCM gets data from the HVAC unit, relay control module, and gauge control module.

Here is where I am confused.

The B-CAN self diagnostic without a HDS in my shop manual should repeat codes by flashing the dome light by shorting the MPCS Service connector on the under-dash fuse box. A code 11 (long flash + short flash) flashes only one time and the cluster shows "no" meaning no B-CAN DTCs stored. Code 11 is listed in a table at the end showing a code 11 is for the relay control module. It is not clear if the dome light or the cluster would flash this code. Checked the proper connector under the fuse box in engine bay and the pins look good. Still need to test the wiring.

I need to figure out what component is signaling to the PCM to turn on the a/c. Going to repeat in test mode 2 and test specific components.

As for the compressor, it is likely shot. Going to pull the hoses to see if metal shavings in them to determine what needs replaced.

If you have suggestions, let me know. I'll keep working on it. Not having a HDS makes this type of work extremely difficult.

 

First my sympathies Losing AC in the current Houston heat wave is a blow!

Have you checked the AC pressure switch for shorted pins? Suggest unplugging the pressure switch to see if any change.

Also a stuck AC compressor relay (fail closed) would cause your symptoms. Pull relay to test if that interupts compressor on. Also check compressor relay control line for ground w/ system off. You should not have a ground. If you don't, then relay was failed closed.

Hopefully, no metal shavings in system. A new receiver/drier is likely needed. A used compressor can be purchased for < $150.

good luck

 

I pulled the lines already. The large low pressure line had metal shavings. I just used rinsed with denatured alcohol and drained onto a white paper towel.

The high pressure lines had none. Flushed the low pressure line with a garden hose, then with denatured ethanol. No more metal shavings. I'll repeat a few times to be certain.

I'll probably reuse the lines. New condenser, compressor, and expansion valve. I'll try flushing out the evaporator. The CRV has a similar, if not identical, compressor. I read where a piston driven Denso was used on the CRV. I wonder if something similar is out there for the TSX?

I'll test the compressor relay pins to see if something strange is happening. Both fans turn on and the compressor immediately when the key is turned on. They are grounded by separate wires by the PCM.

TH- Thanks for the reply. This is not going to be fun.

 

I can't really help much right now.

But, this is some info. regarding the TSX HVAC system:

HVAC
How the Circuit Works
The Audio-HVAC display panel controls the blower
controls, air delivery, and A/C compressor controls
either automatically or semi-automatically. With the
ignition switch in ON (II), battery voltage is
supplied through fuse 30. The Audio-HVAC display
panel is grounded at G503.

Fully-automatic Operation
To put the HVAC control in fully automatic mode,
press the AUTO button and set the fan control dial
to AUTO, then set the desired temperature by
turning the temperature control dial. FULL AUTO
will appear in the system’s display.

The system automatically selects the proper mix of
cooled and/or heated air that will, as quickly as
possible, raise or lower the interior temperature
from its current level to the set temperature. The
system also adjusts the fan speed and changes
the direction of air delivery.

When the temperature is set to its lower limit
(60_F/18_C) or its upper limit (90_F/32_C), the
system runs at full cooling or full heating only. It
does not regulate the interior temperature. When
the temperature is set between the lower and
upper limits, the system regulates the interior
temperature to the set value.

Semi-automatic Operation
Various functions of the HVAC control system can
be manually selected in FULL AUTO. All other
features remain automatically controlled. Manual
selections cause the word FULL to go off.
However, when you select A/C OFF, the system
cannot regulate the inside temperature if you set
the dial lower than the temperature outside.

Blower Controls
The fan speed is automatically controlled in the
Full Auto mode. The fan speed can be manually
selected by turning the fan control dial clockwise,
just past the AUTO position. This takes the fan
from automatic mode to its lowest manually
controlled speed. Turning the dial further clockwise
increases the fan’s speed, which increases airflow.

Battery voltage is applied at all times through fuse
21 to the blower motor relay contacts. With the
ignition switch ON (II), the blower motor relay is
energized which feeds battery voltage to the
blower motor. The blower power transistor controls
the blower motor in all speeds except HIGH. The
blower power transistor is controlled by the climate
control unit. When the Audio-HVAC display panel
requests HIGH blower speed, the blower power
transistor grounds the blower motor, which
connects the blower motor directly to ground,
making the blower run at high speed. In cold
weather, the blower will not come on automatically
until the heater starts to produce warm air.

Air Delivery
The Audio-HVAC display panel controls the blower
motor and supplies a 5 VDC reference voltage to
the driver’s air mix control motor and the front
passenger’s air mix control motor.

The air mix and mode control motors all receive
inputs from the Audio-HVAC display panel. The
driver’s and front passenger’s air mix motors
regulate the mixture of cold and hot air by varying
the position of the heater-evaporator doors. The
mode control motor controls the direction and
volume of outlet air. Use the MODE button to select
the vents the air flows from, although some air will
flow from the dashboard corner vents in all modes.
Each time you press the MODE button, the display
shows the mode selected. Press the button four
times to see all the modes. The air mix control
motors and the mode control motor are grounded by
the climate control unit.

The recirculation control motor receives battery
voltage through fuse 30 with the ignition switch in
ON (II). The recirculation control motor regulates
the position of the fresh/recirc door, and is
controlled by two position inputs from the climate
control unit (“Recirc” and “Fresh”).

A/C Compressor Controls
Battery voltage is provided at all times to the A/C
compressor clutch relay contacts through fuse 9.
With the ignition switch in ON (II), battery voltage is
supplied to the relay coil through fuse 30.
With the ignition switch in ON (II), the climate
control unit grounds the A/C ON input of the
ECM/PCM through the multiplex integrated control
system and the A/C pressure switch. The
ECM/PCM then grounds the A/C compressor clutch
relay coil. This energizes the coil, which closes the
relay contacts and provides battery voltage through
fuse 9 to the A/C compressor clutch. The clutch
then engages and begins turning the compressor.
By default, when the climate control system is on,
the A/C is on.

 

A stuck AC compressor relay is unlikely since both fans and compressor were running.

There is the relay control module and gauge control module between the ac pressure switch and the ECM/PCM. Perhaps one of these is defective, if it's coupling a ground signal from AC pressure switch to the ECM/PCM. There is no info on these components, but a long diagnostic on AC Pressure Switch and Thermal Protector Circuit Troubleshooting.

You may be able to find a axial piston compressor that is a substitute for the scroll compressor. Suggest checking w/ ackits.com for compressor options.

The scroll compressors work well but perhaps are more prone to catastrophic failure than axial compressors. That seems to be the case for TSX's, but we haven't seen many posts here about Accord compressor failures, at least that is my impression.

good luck

 

I am going to give a followup. The A/C is fixed.

Replaced the compressor with a new scroll compressor. The parts guys said that the clutch was hitting the sub-frame on CR-Vs with the axial/piston style and won't sell them anymore. This was the 1-800-radiators warehouse in Houston. I could tell the parts guy knew what he was talking about, so I took his advice.

Replaced the evaporator with a used one from a TSX with working a/c. Had to straighten some fins. The use of tweezers makes this pretty simple and worked best, but tedious. There is a youtube video on it. Then I cleaned the coils with some coil clean from Lowes.

New expansion valve and o-rings (Honda/Acura OEM). Condenser was TYK from RockAuto.

Got everything back together. Pulled a vacuum on it last evening. This morning, the pressure hadn't changed.

Bought a can of R-134a with 510 grams (spec in shop manual is 500-550 grams R-134a). I don't like using oz, because fluid oz and weight oz are different. System pulled the contents quickly.

The a/c controls are now working properly.

I accidentally received a compressor for a CR-V. Noticed the thermal protector cuts power supply directly to the compressor clutch. On the TSX, the thermal protector and the a/c pressure switch are in series and supply ground to the relay control module.

I like the CR-V setup, because a compressor overheat will cause the clutch to disengage. If there is some short to ground on the TSX, or other electrical fault with the relay control module, then the compressor will keep running. I like the CR-V setup better and may rewire to match it.

Still need to measure high and low pressures and vent temperature. My high side manifold hose has a slight leak, so I need to buy new hoses for my manifold. Figured I am close enough on the charge.

Thanks for the tips.

 

Good to hear resolved.

Life w/o AC in Houston is barely tolerable.

good luck