Cooling fan issue

[twj815]

I have a 1995 Regal 3.8 V6.

The only way I can get a cooling fan to operate is to turn on the AC. The car over heats otherwise in stop and go driving. Only the driver side fan comes on with the AC on. I have swapped fan relays with no change. I have jumped across the contacts of the other fan's relay and that fan will operate. Both relays and fans are good. There has been no check engine light. This car has a 12 pin OBD1 connector.

Should both fans operate with the AC on? When the temperature gauge goes above normal, the car will eventually start running rough and will stall while idling. Then it can take up to 2 hours to get it to start again.

Is there anything else I should check before ordering a new PCM?

 

[HotZ28]

Have you tried disconnecting the Engine Coolant Temp (ECT) to see if both fans come on? Do you have a coolant temp gauge, if so, does it appear to be reading normal, if not, use a scanner to read ECT. Have you checked the ECT sensor resistance at cool temps & hot? How about the thermostat, is it fully open when @ the designed temp? I suspect, there is something other than the fan operation causing the overheating condition. BTW, what is ambient temps where you live when this overheating event occurs?

 

[twj815]

The temp gauge seems to be working. The temp goes up way above normal if the fans aren't running. With the AC on (and one fan running) the temp stays close to normal. Ambient temp doesn't seem to matter. It overheats at 10 degrees or 50 degrees. We've had a colder than normal winter. Disconnecting the ECT only turns on one fan (driver side.)

 

[HotZ28]

When disconnecting the ECT, both fans should run. This acts as a fail-safe mode to prevent overheating in the event of ECT sensor failure. Since this does not happen, that tends to point to the PCM, or associated wiring. IIRC, in 1995 one fan should run on low speed with the A/C turned ON, provided that the ambient is above 40° and compressor is running and developing pressure. Fan turn on in A/C mode is controlled by the refrigerant low/high pressure switch, the ECT (engine coolant temperature) sensor, the PCM and the cooling fan relays. Without the A/C turned ON one fan should turn ON (low speed) when coolant temps reach 220-230°. If coolant temps reach 230-240° both fans should turn ON high speed. I assume the coolant has been serviced on a regular schedule (every 3-yrs)?? Before replacing the PCM, remove the thermostat (while cool) and place it in a pan of water on the stove. Bring the water temp up to the thermostat temp rating (195° OEM) and see if it is fully open. You should see a gradual opening begin around 170°.

 

[buickfan235]

Hope you were able to get it resolved. HOTZ28 is spot on

 

[twj815]

Not resolved yet. It's been too cold to do anything to it. Now I can't get the AC compressor to engage when I turn on the AC and neither fan runs. As long as the car keeps moving at these temps it doesn't get hot. It still refuses to restart if it is turned off after it has been running for a couple hours straight.

My wife uses this car to deliver newspapers in the middle of the night. With temps in the single digits and her watching the temp gauge she has been able to keep working. The heater works great for her.

 

[twj815]

Here's an update: I replaced the thermostat (195 degrees) as opposed to testing the old one but there has been no change. In fact things have become stranger. Sometimes the AC works and the fan runs, sometimes the AC and the fan don't work and sometimes the compressor works but the fan doesn't.
Sometimes the car won't start even when it is cold. It cranks and has spark but sometimes won't start unless I floor or pump the accelerator.
Sometimes it runs smooth, sometimes it idles rough.

I find this all quite weird. But it doesn't overheat if I can keep the AC fan running. I still haven't seen the one on the passenger side work.

 

[dubby9953]

My problem as we speak.. currently have it at big o tires to see what they say . Currently bought an ac compressor and cooling fans.. haven't put in yet....my fan 3 relay keeps blowing out thou.. not sure if you checked that.. I also get cold air occasionally