90 Honda AC Problem

My 90 Honda prelude Si's AC works Fine 1st thing in the morning, However
after about 15 minutes the red light on the AC switch comes on which
indicates the compressor cut off. The AC will then not work the rest of
the day. Red light will come on within 10 seconds after turning the AC
on.

HELP PLEASE!

 

The first thing I would check is the system pressures. The compressor
can be erratic (due to low pressure sensor) if the refrigerant charge
is low.

Professor
www.telstar-electronics.com

 

Your '90 Prelude has a compressor clutch slippage detection system. The red
light in the switch indicates one of two things: either the ac clutch IS
slipping or, the detection system THINKS the ac clutch is slipping.
The crank shaft pulleys delaminate on these occasionally, that could be the
problem, or the compressor has developed a leak at the front seal.

Here are some tips from Honda's own Service News from September '00


A/C Warning Light On:
’88–91 Prelude
On ’88–91 Preludes, the red A/C warning light comes
on when the speeds of the A/C compressor pulley and
the crankshaft are different for more than 3 seconds.
Here’s what can cause the speeds to differ, and how to
repair the possible problems:
Crankshaft pulley separation. On some models, a
rubber insulator joins the hub and rim of the
crankshaft pulley. If the bond fails between the
insulator and the hub or rim, the hub turns with the
crankshaft, but the rim slips on the insulator, making
the A/C warning light come on. To check for this
slippage, draw a line across the pulley. Start the
engine, rev it up, then shut it off. Look at the line you
drew on the pulley. If the marks across the hub and
rim aren’t still lined up, replace the pulley.

Compressor clutch oil seal leakage. On ’88–89
models, a leaking oil seal can contaminate the
compressor clutch and cause it to slip, making the
A/C warning light come on. Inspect the compressor
clutch oil seal, and replace it if necessary (see S/B
88-038, A/C Compressor Front Seal Leakage, filed
under Accessories).

Compressor pick-up sensor. On ’90 models, a
defective pick-up sensor can send a false signal to the
compressor control unit, making the A/C warning
light come on. Check for a defective pick-up sensor,
and replace it if necessary (see S/B 90-019, A/C
Compressor Pick-up Sensor Set Replacement, filed
under Accessories).

Compressor control unit. If the A/C warning light is
on without any of the above problems, use an 8X
magnifier to inspect the solder joints inside the
compressor control unit. If any of the solder joints
are cracked, clean and resolder the printed circuit
board, or replace the compressor control unit.

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Interesting... but how is the compressor speed sensed?

Professor
www.telstar-electronics.com

 

Thanks guys, yall rock.
Have narrowed the problem to heat. have the car in my shop, which is
airconditioned and the compressor cuts off when the engine gets up to
running temp. also noticed that the cooling fan relay is gone. Weird. I
didn't take it. I Know its not the pressure switch, AC relay 1 or 2, or
freon pressure system is fully charged. When the engine cools its fine.
is there a temp sensor or switch that I can't find and if so where would
it be.

 

Really weird that the condensor fan relay is missing. I don't remember where
it is mounted, but assume that you only have half the fans running (rad)
that should be when the AC is on, unless somebody rewired things?

As TomP speculated, I actually experienced the pick-up sensor failure in my
90 Si ALB after 8 years. It was intermittent, but usually would only fail
after work (sitting in the HOT summer sun all day), but hardly ever in the
morning. Try measuring the sensor resistance (engine & key off) when hot at
the 2 pin connector near the compressor, or just use needles to pierce the
wires (I found the 2 sensor wires--white(gnd) and green(signal)-- in the
spiral wrap jacket running across the radiator below the bumper-easier for
me than trying to get my hands on the connector).

My bypass circuit uses the ECU "AC Request" signal, shifts it to 12V through
a PNP transitor and passes it to the coils of compressor clutch relays A and
B. Slipping/stalled sensing is disabled, but most cars don't have it
anyway. Here's what I reported to some others 3 years ago on the same
subject :

Hi,
I had this same problem on my '90 Prelude SI. Honda had a Service Bulletin
against a group of Sanden AC compressors (Bulletin No 90-019 July 27, 1990).
My symptons were that the AC compressor clutch would cut out after about 1-2
seconds of running and the red error LED would come on in the AC switch.
After pushing the AC switch on/off three times, the speed sensor module
completely locks out the compressor clutch until the ignition is turned off.
The
bulletin listed normal sensor impedance as 365-445 ohms at 68 degF., but I
think the manual had the numbers a little higher. When my sensor was
intermittent, it would read as an open when failing. As you probably found
out, you can't replace the sensor without removing the compressor (ac hoses,
splash panel, recharge R-12). And you can't
simply short across the sensor since the control module "counts" the
revolutions of the compressor vs the engine to make sure the compressor
isn't stalled.

I built a simple one transistor (with bias resistors and protection diodes)
circuit to replace the sensor module ('90 was mounted up behind the glove
box on the side kick panel under another warning module (seat belt??). It
worked for me for another year while I had the car and was still working for
the next owner. The same design worked for another lude owner (I think '89)
who built the circuit in June 2000.

I've scanned the service bulletin and my hand drawn circuit and can post
it here or send it to you. All of the parts are readily available (Radio
Shack, etc). The only tricky part was finding pins for the module mating
connector. I wanted to maintain the 12 pin harness connector in case I ever
had to reinstall the original module (a 24 pin ic with a slew of
transistors, etc.). I found a connector with the exact pins (but not the
right shape connector) at a local electronics part store and just taped the
new circuit's wires in place after mating them to the harness.

J.

 

J.
Awesome feedback. If it is not to much to ask could you email the
circuit schematic to me, assuming you still have it to
. You'd be such a hero in my book.
Thanks
Jon