Fan clutch does not engage with A/C on at idle

[sclord2002]

I was doing a periodic run up on my 2006 Volvo 780 with D12D engine and Turned the A/C on with truck idling....no cold air...HMMM. Checked A/C compressor and its clotch was engaged and compressor turning, line to condender was very hot and condenser was hot. The A/C  seems ot work well enough when going down the road.  The engine cooling fan was freewheeling and not moving air through condenser and radiator. The fan clutch does engage when engine temp gets to 200 degrees , so this tells me that the fan air solenoid is working and the fan clutch is working but I don't know how the A/C tells the air solenoid to close to engage the engine fan clutch. Is it through a relay actuated by the A/C ON button or is it temp controlled. It would not make sense to me for the fan to be engaged any time the A/c is on, since ram air is sufficient when moving.  I am thinking  that a temp sensor on the condenser or high side refrigerant line would control the engagement of the fan. If anyone has real world knowledge or experience with any of this, I would really appreciate your input. Oh, I did find how to wire in a manual fan clutch switch but I would like to understand why the fan is not working with the A/C on at idle. Thanks in advance.

[Darryl&Rita]

Too lazy to look up the wiring diagrams for a Gen 2 Volvo on the Resource Guide, but there should be a relay to engage the fan clutch.

[Star Dreamer]

I don't think our fan clutch engages on our Freightliner at idle with the AC on. We have Detroit 14L.

[Jaydrvr]

58 minutes ago, sclord2002 said:

I was doing a periodic run up on my 2006 Volvo 780 with D12D engine and Turned the A/C on with truck idling....no cold air...HMMM. Checked A/C compressor and its clotch was engaged and compressor turning, line to condender was very hot and condenser was hot. The A/C  seems ot work well enough when going down the road.  The engine cooling fan was freewheeling and not moving air through condenser and radiator. The fan clutch does engage when engine temp gets to 200 degrees , so this tells me that the fan air solenoid is working and the fan clutch is working but I don't know how the A/C tells the air solenoid to close to engage the engine fan clutch. Is it through a relay actuated by the A/C ON button or is it temp controlled. It would not make sense to me for the fan to be engaged any time the A/c is on, since ram air is sufficient when moving.  I am thinking  that a temp sensor on the condenser or high side refrigerant line would control the engagement of the fan. If anyone has real world knowledge or experience with any of this, I would really appreciate your input. Oh, I did find how to wire in a manual fan clutch switch but I would like to understand why the fan is not working with the A/C on at idle. Thanks in advance.

On my '99 Volvo the fan is controlled by the ecm, based on input from multiple sensors. In fact, my ecm is set for the fan to always be on at idle if the a/c is on, which for me is always. Jay

[DesertMiner]

A/C “high” pressure switch sends info to the ECM to “turn on/off” the fan. Might be low on  freon.

Edited July 15, 2020 by DesertMiner

[dlcarsonak]

   Have you tried to use the High idle? On low idle the Alt. may not produce enough electric to run everything. Just my thoughts.

  I had a student that let his coach idle all night, then he had to buy a new Alt.

   Check cabin air filter.

Edited July 15, 2020 by dlcarsonak

[Jaydrvr]

2 hours ago, Star Dreamer said:

I don't think our fan clutch engages on our Freightliner at idle with the AC on. We have Detroit 14L.

I think that's the normal setting. I think the fleet that owned my truck set them all to come on at idle. Jay

[Moresmoke]

I think the fan is triggered off refrigerant pressure. Been a while so I may be wrong.

[Darryl&Rita]

With the wisdom of Volvo, it should be an ECM output, driving a relay.
Edit to reflect merge of 2 threads.

Edited July 16, 2020 by Darryl&Rita

[Jaydrvr]

3 hours ago, dlcarsonak said:

   Have you tried to use the High idle? On low idle the Alt. may not produce enough electric to run everything. Just my thoughts.

  I had a student that let his coach idle all night, then he had to buy a new Alt.

   Check cabin air filter.

Neither of those scenarios has ever happened to me... yet... But it's only been thirty or so years. Maybe next year. I seriously doubt that one night of idling killed an alternator. Otherwise, there would be a LOT of trucks needing alternators. Jay

[Nigel]

Charlie

Could be as simple as radiator fins plugged up with dust and bugs.  Have you tried flushing from the fan side to the front with a garden hose?  Your truck probably never has enough load to even tax a radiator with restricted airflow.  
 

Nigel

[RandyA]

Charlie - the air solenoid that controls the fan is on the right inside of the frame under the passenger.  If memory serves me correct there are a total of five solenoids built into one unit that control other devices.  The wires for the AC solenoid go directly to one of the sub-ECM driven modules and determining what happens there gets fuzzy real fast.  What you CAN do is wire in a new control line with a switch convenient to the driver to apply B+ to the fan solenoid.  To be safe you should put a diode in the OEM signal wire so there is no voltage feedback to the control module that could cause a malfunction.  The diode will cost a loss of .6 volts to the solenoid but the drop is not significant to the solenoid engaging.  You will, of course, need to remember to turn the switch on when idling and off when moving.  I know you are getting old and forgetful so be sure to put a written reminder at the bottom of the instrument cluster 🙂.

[sclord2002]

Randy, maybe the roar of the fan would remind me to cut it off....but then there is that issue of hearing. This getting old crap is getting old......  I did find where applying 12 volts to PA19 of the VECU will allow control  of the fan without triggering any codes that could result from some other fan control methods.

[DesertMiner]

10 hours ago, sclord2002 said:

I did find where applying 12 volts to PA19 of the VECU will allow control  of the fan without triggering any codes that could result from some other fan control methods.

Did you try it....? What were your results?

 

Edited July 20, 2020 by DesertMiner

[usbusin]

2006 Volvo 780 with D12D engine

Per OP 1st post

[sclord2002]

Desert,  due to other things going on right now, I have not tried the 12 volts to PA19 of the VECU.  i will post the results when I try it.  I am a little hesitant to apply voltage to things that could go POOF and cause bigger problems. I am still trying to understand why the fan does not come on at idle when the A/C is on, but have not ruled out a manual switch.

[DesertMiner]

Keep us posted.

I’m curious to see how this works on a Volvo motor

Edited July 22, 2020 by DesertMiner

[RandyA]

To add some to my comment.......  About five years back, on a trip to Indiana, my fan would NOT turn off at all.  My fuel mileage dropped like a rock and the constant roar was more than a little irritating.  We stopped at a campground in PA and I pulled out the electrical schematics and manuals I keep in the truck and learned that my fan clutch was controlled by air.  The source being a solenoid under the truck.  While at the campground I switched the air supply for the fan to a 1/4" line I had added for my added air horns.  I had a spare single function 1/4" air solenoid in my spare parts bag for the air cylinder I had added to assist my clutch and used it to rig a manual fan control that I could turn on and off from inside the cab.  I continued to operate the fan via the switch by checking the temperature gauge for the next 2,000 or so miles.  Back home I discovered that the multiple port solenoid I mentioned had a leak in the body at the fan control end.  It had once also controlled the air for the hitch slider and second axle air locker, which I no longer had.  The only function left was the fan (I may be forgetting something - it has been a while back).  Anyway, being the cheap DIY type I am I bought an adjustable fan switch from a local auto supply for a lot less than what might be needed to replace the OEM solenoid and correct the problem from the VECU.  I poked the sensor into the radiator fins, set the switch for 160 degrees, added a Bosh relay to correct the on-off polarity and continued to use my single port solenoid.  It has been that way since and worked fine.  When I did all this I believe it was Carl that commented that the fan on his later model Volvo was NOT controlled by air - rather it was temperature controlled from inside the fan clutch.  That very well may be what Charlie has rather than what mine does - or did.  So, whatever you do keep in mind that there are at least two different methods used to control the fan clutch and be sure which one you have.

[SuiteSuccess]

1 hour ago, RandyA said:

To add some to my comment.......  About five years back, on a trip to Indiana, my fan would NOT turn off at all.  My fuel mileage dropped like a rock and the constant roar was more than a little irritating.  We stopped at a campground in PA and I pulled out the electrical schematics and manuals I keep in the truck and learned that my fan clutch was controlled by air.  The source being a solenoid under the truck.  While at the campground I switched the air supply for the fan to a 1/4" line I had added for my added air horns.  I had a spare single function 1/4" air solenoid in my spare parts bag for the air cylinder I had added to assist my clutch and used it to rig a manual fan control that I could turn on and off from inside the cab.  I continued to operate the fan via the switch by checking the temperature gauge for the next 2,000 or so miles.  Back home I discovered that the multiple port solenoid I mentioned had a leak in the body at the fan control end.  It had once also controlled the air for the hitch slider and second axle air locker, which I no longer had.  The only function left was the fan (I may be forgetting something - it has been a while back).  Anyway, being the cheap DIY type I am I bought an adjustable fan switch from a local auto supply for a lot less than what might be needed to replace the OEM solenoid and correct the problem from the VECU.  I poked the sensor into the radiator fins, set the switch for 160 degrees, added a Bosh relay to correct the on-off polarity and continued to use my single port solenoid.  It has been that way since and worked fine.  When I did all this I believe it was Carl that commented that the fan on his later model Volvo was NOT controlled by air - rather it was temperature controlled from inside the fan clutch.  That very well may be what Charlie has rather than what mine does - or did.  So, whatever you do keep in mind that there are at least two different methods used to control the fan clutch and be sure which one you have.

Randy,

Great write up and solution. But no my fan clutch is controlled by air. Charlie and I have sister trucks so I’ll bet his also. When I had my fan clutch replaced several yers ago they moved that solenoid off the rail and up on the firewall so would be easier to repair. 

[sclord2002]

Randy and Carl, My truck DOES have the air actuated fan clutch. If no air pressure is applied to clutch, it engages,  If air pressure is applied, it disengages. The fan clutch works fine when driving down the road  if the temperature gets to 200/210 degrees, but not at idle with the A/C on.  The A/C compressor is engaged and the high side line and condenser get hot due to no airflow at idle.  I am 99.375% sure that It used to come on at idle since it used to blow cold air at idle......now it blows cold air when the radiator/condensor gets ram air when traveling but not when stopped and idling. I perhaps wrongly assumed that the freon charge was ok since the high side line and condenser are getting pretty darn hot at idle.  I didn't think it would do that if refrigerant was very low.

 

[RandyA]

Charlie - I feel you already know this but I will put it out there anyway.  If you have no air flow across the condenser you are not going to remove the heat picked up at the evaporator.  Since pressure and temperature rise in concert, your high side line (condenser) will get very hot.  I've know quite a few folks that believe that if they don't have cold air they must be low on "freon" and add more (bad idea without pressure gauges).  Actually, the less freon in the system the colder the air across the evaporator.  That's good when it is very hot outside but when the air temperature is not high enough to melt any ice collecting on the evaporator the evaporator freezes into a solid block of ice, blocking any air flow so there is no cold air.  At the same time temperature at the condenser rises.  That's when you possibly need to add freon using gauges connected to both the high and low side to carefully monitor pressures expected for the ambient outside air temperature.  Our trucks have both high and low pressure sensors/switches that will cut out the compressor clutch if pressures are too far off.  So, as you noted, when your truck is idling (sitting still or in traffic) and the fan is not running temperature and pressure will rise at the condenser and the sensors will disengage the AC compressor clutch and you will not have any cooled air.  It would be darn near impossible to properly charge your trucks AC system unless you vacuumed it down and weighed in the charge with the engine fan NOT running.  So, me thinks you are right - your truck used to run the engine fan when the AC was switched on while idling.  Sounds like you will have to force the fan to run when you connect your gauge set (you do have a R134a gauge set, don't you?) to even begin to get an idea of what your gas pressures are.  I wish I was there to scratch heads with you 'cause you always make me think of things I forgot I have forgotten - that is if I ever knew them to begin with.