madHD

Hello,

I have a 1997 Civic HX 5MT.
AC was evaluated and vacuum held.
Recharged to 45 psi low side and 200 psi high side.
Condenser fan and Compressor clutch work when jumped at relay power side and I get cold air. Blower fan works fine.
Relays are OK, Fuses are OK, pressure switch has continuity across pins.
Connector reads blu/red +5V, blu/wht 12V with key ON.
12V supply to activation side of both fan and clutch relays.
Good continuity from activation gnd side of clutch relay to A17 at ECU.
Good continuity from activation gnd side of fan relay through pressure switch back to B6 on ECU.
Clutch and fan engage when A17 is grounded and B6 is grounded, respectively.
Grounding B6 does not kick out ground at A17.
Pressing the switch on the dash changes the blu/red at the thermostat connector from 60mV to about 6.6V.

It seams to be a bad ECU but I want to make sure? Did I miss anything?

How does pressing the switch on the dash communicate with the ECU? It looks like it is through the blu/red to blu/wht wire from the thermostat which is in parallel to the pressure switch. Is that correct?

What are the consequences, other than idle speed / load, of lifting A15 and B5 from the ECU connectors, running them to a toggle switch to control, then to gnd? I know idle load will go up and the ecu will not know why. It might through a CEL if it doesn't like where the IAC ends up. Any other concerns?

madHD

What are the consequences, other than idle speed / load, of lifting A17 and B6 from the ECU connectors, running them to a toggle switch to control, then to gnd? I know idle load will go up and the ecu will not know why. It might through a CEL if it doesn't like where the IAC ends up. Any other concerns?

Former User

What exactly is the problem? Does pushing the A/C button on cause either the condenser fan to run or the compressor clutch to engage?

You should recharge by refrigerant weight.

The two A/C system ECU pins are A17 and C5.

Pressing the switch from ON to OFF, right?

If you unplug the pressure switch (everything else plugged in), turn the key to ON(II), and then ground the Blu/Red wire terminal in the connector to the chassis, does the clutch engage?

The A/C button in the dash grounds voltage both from the condenser fan relay and from C5 of the ECU. This switches the fan on and also tells the ECU to ramp up the idle speed and, after a short delay, to provide ground at A17 to cause the compressor clutch to engage.

The ECU's involvement in the A/C circuit is only to ramp up the idle speed prior to engagement of the compressor clutch.

canadaek

did you install a/c or did your car come with it ? when i added it to my 96/cx i forgot the a/c diode in the under hood fuse box and my condenser fan wouldn't run .

madHD

It is OEM air conditioning from the factory. The diode is good. Thanks.

madHD

Sorry. Pushing the button will not turn on the condenser fan or engage the compressor clutch.

It amounted to slightly less that 24oz, including some PAG oil (one can had it in).

Actually, this is from off to on.

No.

I have not unplugged the connector from the dash and grounded the blu/red wire yet. Since I am getting about 6.6V from the blu/red wire at the thermostat connector with the button in the ON position this could mean that the solid state replay at the button has malfunctioned, right?

How much of a delay is there between C5 going to ground and providing ground to A17? I may have missed that when I grounded C5 and measured A17.

madHD

Thanks for the help. Ron, you seem to be the Honda AC guru so I appreciate your help.

Former User

A bad ECU alone would not prevent the condenser fan from running. Either the ECU is fine or the A/C circuit has more than one problem.

When the key is in ON(II), the evaporator temp is above 37F, and the A/C button is off, the thermostat should not block voltage to the Blu/Red wire. Therefore, you should read battery voltage at the Blu/Red wire under these conditions.

When the A/C button is pressed under the conditions listed above, voltage at the Blu/Red wire should drop.

With the pressure switch unplugged, do you measure about 5V to body ground at the Blu/Red wire terminal in the pressure switch connector when the key is in ON(II)?

Do this^ test to see whether the condenser fan runs. However, based on the result of your pressure switch connector test, you would not expect the clutch to engage.

If you unplug the A/C thermostat, what voltage to body ground do you measure at the Blu/Wht and the Blk/Yel wire terminals in the connector with the key in ON(II)? You should read battery voltage at both. If so, does grounding the Blu/Wht wire terminal cause the condenser fan to run? Again, based on the result of your pressure switch connector test, you would not expect the clutch to engage.

Just a couple second delay.

madHD

It is looking like a number of problems.

With the A/C button off I read the following the the thermostat:
blu/wht = 10.8V
blu/red = 68 mV
red/yel = 12.5V

With the A?C button on:
blu/wht = 12.0V
blu/red = 75 mV
red/yel = 12.5V

Yes

I didn't pull the connector from the back of the dash but according to the schematic the blu/red wire at the thermostat is the one I would have grounded at that connector. I grounded it at the thermostat and yes, the fan turns on.

Blu/wht = 12.3V
Blk/Yel = 12.6V

Grounding the blu/wht with the connector unplugged from the thermostat does turn the fan on. With the connector plugged in grounding either blu/wht or blue/red turns the fan on.

This is what I think are the problems:
1) the switch on the dash or associated solid state relay is not activating ground for the fan relay.
2) the thermostat is questionable - voltage block to blu/red but also activates fan relay when either are grounded (could be result of dash switch issue?)
3) ECU is not activating A17 to ground to engage clutch.

I wired up a toggle last night to create the ground for C5 and A17. Works but idle is very low - stop and go traffic was difficult.

Thanks again for all the help.

Former User

My mistake. I did not describe the correct test for the type of thermostat in your car. Nonetheless, the test you did below indicates the thermostat is fine.

However, there should not be a Red/Yel wire in the thermostat connector. Instead, there should be a Blk/Yel wire.

As mentioned above, this^ shows that thermostat is fine. It also tells you that one problem is either (i) a bad Blu/Red wire running between the thermostat and heater control panel or (ii) a bad heater control panel. To determine which one is bad, do the original test I mentioned -- ground the Blu/Red wire terminal in the heater control panel connector. If the condenser fan runs, replace the heater control panel.

This^ or the Blu/Red wire is bad (as mentioned above).

It's probably fine.


Yes, the ECU is most likely bad.

First, I highly recommend that you fix the A/C system the way Honda intended it to work. Second, the way you have the system rigged possibly could destroy the compressor.

madHD

Thanks again. I will check the blu/red wire this weekend. I meant blk/yel not red/yel - sorry about that.

Also, I will keep my I open for an ECU. It is the P2N-A22.

Kista20

Check ebay for the ecu there are usually a few of them on there at any given time ranging typically from $40-$75. I also have a 97 hx that the dealer replaced mine for free under warranty when it was somewhere around 136k-138k miles. Make sure you get the A series which is federal spec and not the L because that is cali. From what I've seen the p2n's doesn't seem to last and I am fairly sure that honda had a bad batch of them and I know the 99-00 did. I'm not for certain but I think my original ecu was an A21 but it def. has an A22 in there now.

I also have a 99 that when I bought the car it came with a cali spec ecu and it was the old spec. I kept searching around and finally found a federal one on ebay but had the updated part number so I'm hoping it was one the dealer had replaced under warranty so it shouldn't be too old.

I would finish the tests that Ron has suggested and if comes down to that your ecu is bad then it wouldn't hurt to buy one and then use the old one as a spare since it will run the car just fine and at least you will be able to keep driving it.