marine928

UPDATE PROBLEM SOLVED!! See last comment in thread....We had an issue with the a/c system in my 87 on our way back from Fredericksburg recently. A/C was working fine, wx outside was in the 80's. Stopped for fuel, got back in started car and engaged a/c. System operated for about 5 min. then fan shut off along with a/c illumination light. I recycled air direction on control module including moving slider to defrost.. nothing. Pulled over tried several variations on the control module. Removed fuse box cover in passenger footwell and checked fuses # 6, HVAC controller, 17, HVAC blower. Both were good, I switched them around with new fuses no change. I also checked relay #10 and switched it around with the horn relay, no change. On the way home I would try it and a couple of times and it would come on very briefly. Got home did some research and ended up removing the blower, the fan resistor and center console control box. The motor worked fine when I applied 12 volts to it directly. I cleaned up the electrical motor and connections and it spins freely. The resistor seemed in really good condition, no heat marks, discoloration or pitting. Coils were intact.
I decided to give Roger a call and purchased a new refurbished/upgraded control box. This morning I finally got around to attempting the repair and ran into a brick wall. Here is where I'm at...
1. with key on 1st accessory position no power to control box, or a/c power button. No power to fan, resistor or ac freeze switch in the engine compartment. No power to fuse #6 HVAC controller.
I DO have power to fuse #17 HVAC blower.
2. With key on the full accessory position there is no change to the above with the exception of the seatbelt warning light and engine warning !! on the a/c power box below the controller. I removed all components and tested each connector and had no power to anything. I also reconnected the control box, resistor and fan, then manipulated the control box without success.

One additional observation is that my fog lights are not working and it seems to coincide with my a/c problem. No power to fuse #30. I cleaned and DeOxited every fuse and connector and tested all fuses with my test light. With the exception of the above non working fuses all others work as designed when the key is in the 1st or 2nd accessory position.

Any comments or suggestions will be most welcome. I loaned my relay puller to a friend and he is not available which is the reason I have not pulled any relays, but as I noted in the beginning I did switch the #10 and 12 relay with no success.
Marine 928


Thanks

drscottsmith

I’m not where I can look at a wiring diagram but wonder if you are starting to see your ignition switch go out by losing contact on one of the bus terminals - that could be the reason multiple circuits are not getting power if the contacts are going that power the bus.

Mrmerlin

try moving the key inwards to press the switch part closer to the contacts,
feel up behind the pod to see if the switch is loose.
NOTE while the AC system is in operation.
also replace the X bus relay

marine928

Thanks, drscottsmith, Mrmerlin. I will give those suggestions a try, and report back. MAHALO!

griffiths

Great site forever https://www.nichols.nu/tips.htm

marine928

UPDATE: Per Mrmerlin and drscottsmith, I checked the ignition switch which is not loose. I also moved the key as suggested while manipulating the controls on the control box. I even tried my spare ignition key which looks brand new, again no go. The #10 bus( HVAC) is getting power and the # 17(blower) fuse is good. Still no power to the blower fan, resistor or freeze control under the hood.....regardless of the climate control slider position or ignition accessory position.
Still no fog lights and no power to the # 13 bus or #30 fuse.
The only recent electrical work was replacement of the Cruise control module prior to our Fredericksburg trip. CC works perfectly. I did notice that the #6 bus for power windows seems to get hot after a few minuets with the key on the 2nd accessory position.
One other question. The power windows and sunroof work even when the ignition is off. For the life of me I can remember if that is normal. Also remember that the climate control box was replaced recently with a rebuilt one from Roger.
Any thoughts from everybody? Oh yes, no power to the #6 HVAC controller fuse.

Thanks
Lon

marine928

Update....issue fixed complements of Memerlin. It turned out to be the X bus relay. He suggested that I run a continuity check on all fuses and then to check the x bus for loose blades. I pulled it and sure enough 1 blade was loose. If I moved the relay the fan would turn briefly. I replaced it with a old original I had and it worked perfectly. Ordered a couple more from Roger to be safe. Fog lights work as well.
I Deotixed everything and with all the extra maintenance and parts replacement my AC should be good for another 160k miles.
Thanks to all.
Marine928
Lon

Mrmerlin

FWIW for others reading this in the future.
Please note that relay position X is not the X bus relay .

X bus relay can be in different positions depending on the the year of the CE panel you have.

In many cases the X bus relay can fail to turn on and or stick closed and kill the battery,
an IR gun will find this hot relay after 10 mins of shutdown.

See your year WD to find out what the X bus relay powers. its found in different model years.
It is the key switched power relay (and also one of the 4 running relays found in S4 and later to be replaced)
.when starting or running issues develop.

NOTE damaged relays are usually attributable to a low voltage condition on the battery.
This makes the relays have less closing force when activated,
this in turn can cause the points inside to arc,
and then over time the contacts get dirty and pass less voltage to the system being powered,
this is usually why you have a hot relay while the system is in operation, dirty contacts inside the relay.

Bottom line if the battery is not fully charged in your 928 its prudent to charge it first before attempting a start.

NOTE a battery tender is not a battery charger,I find it best to use 6 amp charger for 4 hours to top up the battery, after a few months of inactivity
then use a trickle charger to maintain it .

the battery will hold a charge longer if the ground strap connection is removed while the car is not being used for more than a week

marine928

Great info. That's exactly where I made my mistake. I wrongly assumed that x bus meant Roman numeral x and did not look any further. 🤨