[cosmicma]

The pressure sensor has a 5v ground and signal wires that's it , its that simple ,so with the system on get your multi meter in there and test it to see if you've got continuity when the systems on .

across the two outer pins ( pins 1 red and 3 black ) should read 5 volts, the centre pin should not give a continuity reading to ground if it does then there is a problem with the wiring

without a HDS there's not much more that can be tested and shorting pins won't really tell you much
shorting pins 1 and 3 stalls the engine apparently ( posted on other forums )
shorting pins 2 and 3 does nothing ( posted on other forums ) and i'm not sure i'd want to put 5 volts to pin 2 which is i presume the signal wire

i know that an open circuit on the connector causes the fans to spin at high speed and the compressor to not engage
i suppose trying a resistor across the signal wire and 5 volts or signal to ground or even across 5v and ground at about 7 - 10k ohms might get a result it would emulate what the pressure sensor does ( sort of ) but not knowing exactly what pin does what it would be guess work

a little on what the pressure sensor actually does

A/C PRESSURE SENSOR
(Triple function)
When the refrigerant is below 196 kPa (2.0 kgf/cm2, 28 psi) or above 3,140 kPa (32 kgf/cm2, 455 psi), the A/C pressure switch opens the circuit to the A/C switch and stops the air conditioning to protect the A/C compressor.
When the refrigerant is above 1,470 kPa (15.0 kgf/cm2 , 213 psi), the A/C pressure sensor switches the radiator and A/C condenser fans to high speed.

i'm wondering if my AC is low on pressure but not low enough to stop ac all together although it was re gassed recently or it is a faulty pressure sensor
it's a catch 22 to swap out the pressure sensor would mean a re gas any way

thinking out loud...

at around 60 degrees c ( about 230psi ) the fans should be switched to high speed
if i can somehow measure the temp at the sensor and it's reading 60deg c or there abouts and the fans arn't spinning at high speed it would be a good indication the sensor is duff

will have a go at that tomorrow
might work

 

[cosmicma]

A/C Compressor Clutch Circuit Troubleshooting (With A/C) Interesting read .

had a look at that while searching for the high speed fan problem but it doesn't really apply the AC clutch works fine

 

[cosmicma]

If I get time today I will test mine and post back some results , with the system running you should get fluctuating voltages across the signal wire and ground indicating that the sensor is functioning correctly.

that would be useful thanks

if your gonna run the engine with the high pressure sensor disconnected make sure you have a obd diagnostics thingy to clear the error code
the tin foil trick will clear the DTC but not the error leaving the PGM FI warning symbol on the dash

 

[cosmicma]

a little more progress but no fixed yet

just checked the AC high pressure sensor and it seems to be doing it's job but what the AC isn't doing is reaching enough pressure to activate the ac fan or should i say that's what it looks like it's doing

from what i can gather the sensor wire should read about 1 volt per 100 psi, to reach the pressure needed to activate the ac fan i should be reading around 2.5 volts
mine is only reading around 1.23 volts with the engine running and up to temp ( AC on full / lo )

the voltage reading seems a little low and could be the reason why the fan isn't kicking in as it should
with having the AC re gassed not too many weeks ago i was reasonably sure it would have been gassed to the right pressure but it looks like it's not

there's definitely pressure in there, enough to allow AC to work but not knowing enough about Air conditioning i don't know if the symptoms i have are caused by the wrong pressure

i have another ac High pressure sensor but it gives the same resistance readings as the one in the car which points to the one in the car being ok ( maybe )

ah well onward and upward

everything is pointing to low pressure apart from the ac works, just not as it should

 

[cosmicma]

more progress...

checked the ac gas level which seemed to be on the ok side but put a little more in which made no difference
swapped out the ac high pressure sensor and re gassed the system and iv'e got air conditioning and the fans kick in and out accordingly but unless i'm looking at this the wrong way it's the engine cooling fan ( passenger side fan ) that starts spinning at high speed ( engine temp doesn't seem to make a difference until hot )
the condenser fan ( drivers side ) stays at low speed unless the engine is hot and they both spin at high speed with ac on.
with ac off and engine hot both fans kick in at low speed at 96 deg c which i think is about right

i thought the condenser fan was supposed to kick in at high speed with the ac

changing the ac High pressure sensor is a bit of a challenge you need to hold the bottom bit to stop it twisting while you loosen the sensor but there's no room to get a spanner in
an open ended spanner bent at 90 degrees did the trick

if the fans ARE working in an odd way it will be down to the under bonnet fuse box
there is a main fan relay inside the box under the fuse panel that is soldered in place that can go faulty and cause odd goings on and has been known to fail

so...

so far i have air con the fans kick in and out at high speed which wasn't happening it just seems to me the wrong one is kicking

 

[cosmicma]

So are you going to investigate the relay that's soldered in ? Any pics

have a read of this thread

http://www.civinfo.com/forum/how-guides-only/43983-fuse-relay-box-disassemble.html

i'm not going to dissemble my own box i am going to replace it with a known good one and see if the fans behave in a different manner

to be honest for the price of another box ( around 20 quid ) it's not worth the time or the cost of a replacement relay so i'm just gonna swap it out and see what happens

 

[cosmicma]

Honda Workshop Manuals > Civic L4-1.8L (2006) > Relays and Modules > Relays and Modules - Cooling System > Radiator Cooling Fan Control Module Relay > Component Information > Locations

that's not the right fuse box for my model car ( 2007/8 2.2 honda civic es ) i think the link you have posted is for the US civic
the fuse box in my car looks like this

the photo is one taken of my fuse box the two relays that you can see are for the AC clutch ( black one replaced with a mitsuba last year ) and the AC fan control relay ( grey one ) the main fan relay is not visible it's soldered to a board inside the box and is basically a non serviceable part

the main fan relay is within the box it's not so easy to determine if it's working properly without pulling the box to bits
although all the fans are now working it seems a bit odd that the main engine fan should speed up when AC is used and not the AC fan which stays at half speed
to me it should be the other way round
because of the way these fans are wired through both relays if one does pack in it can cause odd behaviour like what i am seeing

i will find out when i swap out the fuse box

 

[cosmicma]

ok to sum this up
i think i am done with it now

after trying all of the above i finally got the fans spinning with the air con but i wasn't convinced the right fans were spinning for the appropriate function
ie when air con is being used i would expect the air con condenser fan to be the one to speed up not the engine cooling fan

i changed out the under bonnet fuse box because i am convinced that the main fan relay is duff in my original one
the new fuse box has made a difference to how the fans behave and to me seem about right so i'm pretty happy that everything is as it should be

it would be nice to have some documentation on what the fan sequences are for different modes but so far i have found nothing

 

[cosmicma]

i'm digging this old thread back up again because i believe the fault with the fans has returned

as far as i can make out this is what the 2 radiator fans should do

there are 3 relays that control the 2 fans

relay no 1 controls the coolant fan ( normally open )
relay no 2 controls the AC fan ( normally open )
relay no 3 switches the fans from half to full speed depending on the state of the other 2 relays

if relay no 1 is closed and the AC is off both fans should do nothing or spin at half speed depending on engine temp

if relay no 2 is closed and no 1 is open the AC fan should spin at full speed and the coolant fan should be still
relay no 3 is controlled by the same signal as relay no 2 so changes state when the ac relay closes
relay no 3 has 2 states
the idle state is shorting both fans together via the positive wire on the AC fan and the negative wire on the coolant fan so they spin at half speed
the active state is to isolate the ac fan from the coolant fan and ground the coolant fan to enable it to spin at full speed when relay no 1 ( coolant fan relay ) is closed
if relay no 1 ( coolant fan relay ) is open and the AC relay is closed meaning the 3rd relay will also be active isolating the AC fan from the coolant fan and grounding the coolant fan the coolant fan should be idle and the AC fan should spin at full speed

if all three relays are active both fans spin at full speed

with me so far

this is how i think it all works and this is what is happening

start car from cold AC off no fans spin which i think is normal
switch AC on both fans spin at half speed in time with the engaging and disengaging of the AC clutch
as far as i can work it out this isn't what should be happening and i'm pretty sure what should happen or what did happen is the coolant fan would be idle and the AC fan spins at full speed in time with the engaging / disengaging of the AC clutch while the engine is cold

i can make this happen by changing the state of relay no 3 which basically isolates the coolant fan from the AC fan and grounds the Coolant fan
in other words by changing the state of no 3 relay the fans are now independent form each other and when their relevant relays close spin at full speed which in my way of thinking is how they should behave
both fans spinning at half speed is only possible if the AC relay is open ( AC off ) which would be normal if the engine was up to working temperature

as far as i can tell whats causing this is a non serviceable relay buried in the middle of the under bonnet fuse box
there are only 2 serviceable relays within the box, one is the AC clutch relay and the other is what i have labelled relay no 3 which is the other relay you can see sat next to the AC clutch relay better known as the fan control relay
the coolant fan relay ( relay no 1 ) and the AC fan relay ( relay no 2 ) are buried inside the under bonnet fuse box

i cured this problem the first time by replacing the fuse box which worked for a while but now i'm stuck with the same problem which has got me thinking unless this is quite common and there a number of cars showing the same symptoms it might not have been the fuse box after all and i just got lucky some how

the control relay is fine iv'e checked it and it works as it should, the 2 internal relays i havn't checked it would mean pulling the fuse box apart to get to them but i might have a go at the old fuse box and see what state the 2 relays are like in that

it gets confusing trying to work out what should be going on if anybody can shed some light on this i would be grateful