a/c compressor cycles and radiator fan not running

Post by **Ozark Lee** » 13 Aug 2009, 02:22

I think you will be fine with the engine running. People are terrified of screwing something up with the A/B boxes but you can't hurt anything even if you tried.

...Lee

240tim · Post by **240tim** » 13 Aug 2009, 17:32

i tested the fi-ecu today in test mode 2 with the engine running.

with the ect disconnected (which makes my fan run) i get the right code 1-1-4. with the a/c on (and cycling on and off) a 1-3-4 staggers out, all as expected. while i was there i tried test mode 3 as well. the injectors and the iac both tapped away happily...

i keep thinking i must have moved something when i was messing about with the oil trap replacement. i also removed the throttle body and cleaned that. i removed the fan assembly to get space in the engine bay. perhaps, i plugged some electrical connector together backwards or poorly, or knocked some other connector - ? i am sweating over these electrical diagrams - they aren't my strong point.

where to go from here?

many thanks,
tim

240tim · Post by **240tim** » 15 Aug 2009, 08:35

i would summarise that:

1) radiator fan does not appear to respond to high water temp
2) radiator fan does not run and a/c cuts out when a/c reaches high pressure

any ecu experts got any troubleshooting suggestions?

tim

Post by **Ozark Lee** » 15 Aug 2009, 08:47

Without decent schematics (which I have not found) and a logic analyzer component level repairs on the ECUs are futile. It becomes a replace with known good exercise.

There are gobs of them on eBay - just match the numbers.

...Lee

Post by **Sperry** » 15 Aug 2009, 20:07

My '94 850 Turbo may have a similar, intermittent issue.
Occasionally, stuck in traffic, the cooling fan may not be going to high.
I swapped Fan Relays today, and everything worked fine, even when the temp readout said HI.
I guess that means it is over 150˚F under the hood?

I'm beginning to wonder if my coil finally has the slow leak,
or if there is an intermittent short in the wiring to the fan relay.

Thanks for the tip on Test Mode 2 & 3

On 850 and 960, cooling fan is operated by a relay, either in response to engine temperature signal received by Motronic control unit or directly by pressure switches mounted in A/C high pressure line.

ksdst1 · Post by **ksdst1** » 23 Aug 2009, 16:53

Hi Tim. I am having the same situation with my 96 850GLT. Fan isn't coming on with a/c or engine heat up, the compressor clicks on and off when i turn the a/c on. Can you please let me know what solution you have finally found to your problem?
tnx kevin

240tim · Post by **240tim** » 25 Aug 2009, 13:22

just a follow up on this saga. finally got things happy again and i've been driving the car and a/c hard for a couple of days to check.

1) it turns out i was low on a/c refrigerant. i jumpered the low pressure sensor and the a/c would run continuously. previously, i mentioned it was cycling from 20 to 40 psi. this was because the compressor would run and suck the gas out of the low side which would reduce the pressure there. it looks like the low side pressure switch turns off the compressor at 20 psi to protect it. i put 2 cans in and it runs nice and cold now. i could only get it up to 30 psi low side pressure while running continuously. now, i will watch for signs of degraded a/c that might indicate a leak.

2) i tried swapping the fuel injection and ignition ecu's. everything did start working while i had the new ones in, but i have swapped back the original units and things still work so i not sure if that helped or not - anyone want to buy a pair of good '93 ecu's?

once i had the a/c running i was confident enough to run the engine hot and see if the fan would come on. it did. maybe i hadn't getting the engine hot enough to trigger the fan, but with the threat of blowing the head 'gasket' if i was wrong i didn't want to take the chance. i was also nervous since i had read that the fan is always on when the a/c is on, but i think that is only true when the engine reaches running temperature. since i was too nervous to run the engine hot i don't think i was reaching high enough coolant temperature. also, i just happened to be unlucky that my a/c lost enough pressure while i was working on my car and i thought it was due to the work i had done.

i also notice that the engine and the ecu box gets pretty hot when things are running normally. i guess i hadn't noticed that before.

lee, many thanks for your help and encouragement. i don't know what i would have done without someone to bounce my thoughts off. thanks for the pointer to the 95 docs.

sperry, try the ecu test modes. i think this will work for 93-95 models with the push button diagnostics. i am not sure how you would trigger these modes on the obdii interface. perhaps the scanners can do it...

kevin, i'm not sure how you could run your ecu in the test modes (i think the 96 has the single ecu). you may have to do all the manual fan system tests i did at the beginning of this thread. the next most valuable trick i found was jumping the low pressure sensor near the firewall and running the a/c compressor. i used a pressure gauge to watch the low side pressure and would only run for short periods with the jumper in since i read it is bad to run the compressor at low pressures (it makes sense since there is a low pressure cutout sensor).

while i was looking through the wiring diagrams i realised there is a lot of feedback between the 2 ecu's - more than i expected. i'm still not sure why the a/c initially cycled fast with the fan off and ran continuously with the ect sensor disconnected (and the fan running). bug in the ecu, maybe?

also, is the pinout of the a/c relay right in the wiring diagram? the info in the '95 docs didn't seem to match my '93 reality.

tim

ksdst1 · Post by **ksdst1** » 25 Aug 2009, 16:34

Tnx for all the good info Tim and thats great that you got her running properly again. Unfortunately for me, I'm still not sure what's wrong with my fan.

Again, I jumped the fan and relay to make sure the fan and relay worked. I then recharged with two cans of 134a. The compressor stopped cycling quickly and I was getting cool (not cold) air but the fan never cam on. Like you I am nervous to overheat. While running the a/c the temp gauge got to about 2 o'clock. Did you find that your engine needed to get hotter for the fan to come on while running the a/c?

Tests modes with the OBDII port are over my head. I don't have a code reader either.

So my bad luck. I'm not sure where to look. Hopefully not a new ecu b/c i think they are mucho expensive.
kevin

240tim · Post by **240tim** » 25 Aug 2009, 17:17

kevin,

i never let my temp gauge go above 3 o'clock before i turned the engine off while i was testing. i don't know i would let it run to 2 o'clock...for long...

my ecu would drive the fan when i unplugged the ect sensor and started the engine regardless of the temperature. apparently, this is normal. since you know the fan and relay work you might try this to see if the ecu can drive the fan. it is possible the wires between the ecu and the fan relay are damaged. check that first. i even pulled the ecu and checked the 2 wires with a multimeter to verify they were good.

perhaps someone else familiar with the later ecu's can recommend a way to get yours into the test mode. i'm really sorry, my (limited) knowledge is limited to the earlier types. amazing for a car with such a short production run!

p.s. do you know how your car got into this situation? i mean, what led up to this issue?

o.t. i did realise my laptop would make a great oscilloscope and diagnostic aid (with the right app) while i was troubleshooting all this. with a little bit of circuitry to sample voltages and waveforms you could have a complete realtime analysis system...

tim

ksdst1 · Post by **ksdst1** » 25 Aug 2009, 19:59

Tim....if i understand your thinking, i did disconnect the ect wires and the fan egaged at high speed and stayed on until a few minutes after the car was shut off. Should I be able to assume that the ecu drove the fan and thus it is not the problem?

The history is a bit complicated b/c of timing. About three years ago I installed a new radiator after i was told the old one had a leak. I also installed a thermostat (but didnt know to change the ect). I drove it for about 9 months and didn't have an overheating problem then but it was fall so no more hot weather. However during the summer one time when i was stuck in traffic when it was a hot summer day, the temp gauge jumped quickly to the two o'clock position but went back down as soon as i started to move again.

Shortly after i stored the car in a barn for two years, recently removed it, had the front brakes done, got it inspected, drove it to columbus and back (4hrs away) and at the end of that trip i got stuck in traffic again during hot weather and the temp gauge went up until i started to move again.

I hit the forum here and some folks pointed to the fan and thats when i realized it was not turning on. The a/c had never worked properly since i bought the car used. Semi-chilled after a charge but i noticed the compressor click, click only recently.

I'll research the thermostat more. I don't know if i can assume the ect is good just b/c i disconnected it and the fan went on. And I'm not sure if the ecu would still be a factor if the fan worked when i disconnected the ect and the fan worked.

Anyhoo, tnx for the interest and effort to help!
Kevin

a/c compressor cycles and radiator fan not running

Re: a/c compressor cycles and radiator fan not running