TheSamba.com :: View topic - When should A/C trigger high speed radiator fan?

Wed Sep 09, 2015 3:22 pm

I confess I don't know how the A/C actuates the radiator fan speeds.

'87 Westy with Subaru 2.5. Replaced all hoses, receiver drier, expansion valve, held vacuum 24 hours, charged with Redtek by Alaric. Only been using it a couple of days now. The system blows reasonably cold.

I noticed that when the temps are in the high 70's to low 80's (but really high humidity, like 70%, so A/C is needed) that only the low speed radiator fan is on. (I believe that fan level is always supposed to be on at a minimum). But when the temps are up in the low 90's the high speed fan comes on after only about 30 seconds of running and does not go off, no matter whether I am on the highway or in traffic. Is this a normal condition? Seems too much to me. I was expecting it to maybe cycle on in traffic but not be on so soon and all the time.

BTW, the engine stays nice and cool in traffic with the high speed fan on.....

Alaric and I drove it around with his gauges attached and he thought the pressures looked OK. 190-230 high and 25-40 low, varied with rpm.

Any thoughts?

What triggers that fan anyway? (I guessing the high pressure switch?)

Wed Sep 09, 2015 3:33 pm

Your van has a 3 speed radiator fan. You are hearing speeds low and medium.

Low rad fan comes on automatically with the A/C. Also when the radiator temp switch says the radiator is too hot.

Medium rad fan comes on from the high pressure switch in the A/C line. If freon pressure stays high enough the fan will stay on medium.

High speed rad fan only comes on when the radiator temp switch says the radiator is way too hot. This is not directly controlled by the A/C. When rad temp switch turns on high speed rad fan it also disables the A/C compressor clutch to reduce the load on the engine so the engine can be saved from overheating damage. This means the A/C stops cooling when the radiator switch turns on high speed rad fan.

Mark

Wed Sep 09, 2015 3:39 pm

Got it. My bad. It is the medium speed that is coming on. It is pretty energetic, I'd hate to see what the high speed sounds/feels like. :shock:

So is it normal for the high pressure switch to activate the medium speed fan for that long? I'm guessing that maybe the system is running somewhat higher pressures than desirable...???

Wed Sep 09, 2015 4:09 pm

Walking down the street in the summertime or sitting in a parking lot at the grocery store can be very instructive. By listening for the click of the AC compressor, you can see and hear the various condenser fan setups on the cars.

There is no universally right or wrong way to build a condenser fan system.

Some are built on feedback loops. In the case of the Vanagon with factory AC, a trinary switch will help regulate the stage 2 fan, turning the fan on or off based on the pressure in the refrigerant system.

You would be right to think that a condenser fan serves little purpose when you are driving 65mph down the freeway, and there are cars out there with speed sensors that override the condenser fan at higher speeds.

On my Volvo 240 I have the condenser fan configured to run anytime the AC thermoswitch is in the "on" position. That means it runs even when the compressor is not compressing.

On my Vanagon with Small Car front AC I have the stage 2 fan run anytime the compressor runs. I tried the trinary switch setup but didn't like the results. I have a small switch on the dash that allows me to turn of the stage 2 fan function completely when driving at freeway speeds.

The stage 2 fan in this configuration cycles intermittently with the compressor with longer running intervals at lower speeds or lower engine RPMs, and shorter running intervals at higher speeds (more naturally forced air) and higher engine RPMs.

The Vanagon radiator/condenser fan is quite a stout fan. It has the potential to consume a relatively large amount of current and make a lot of noise. I made sure my whole system--alternator, wiring, grounds, etc. was built properly for the demand of worst case scenarios: headlights, wipers, AC, blowers, etc. I had that situation on Memorial Day of this year, driving through torrential rains. We had no problems.

One thing I've noticed with the stage 2 fan setup in my van is that its operation contributes significantly to overall moderation of the coolant temperature. On the hottest days it actually helps to run the AC in my van, because it cools the cabin and cools the radiator (and by extension, the engine). This phenomenon seems to be unique to my van.

I've driven about 8000 miles in summer heat since Memorial Day and haven't noticed any issues with this setup. I do think about my fan motor and how it might be getting more use than it was designed for, and an aftermarket electric condenser fan mounted in front of the condenser might be in my future. Replacement Vanagon fans are over $200 and becoming scarce; small electric condenser fans are $20 to $50 at auto parts stores.

I hope this information helps.

kourt

Wed Sep 09, 2015 7:47 pm

dobryan wrote: Got it. My bad. It is the medium speed that is coming on. It is pretty energetic, I'd hate to see what the high speed sounds/feels like. :shock:

So is it normal for the high pressure switch to activate the medium speed fan for that long? I'm guessing that maybe the system is running somewhat higher pressures than desirable...???

wonder how loud????? So loud that when the fan switch fused closed one night when my van was parked on street and I sound asleep at 3 am it woke me up, also woke up neighbor. Pulled the battery cable and went back to bed, ordered a new fan switch next day. The fan on High is VERY loud!!!!!!

Wed Sep 09, 2015 8:03 pm

As others have pointed out..you are hearing the first two speeds of a three speed fan.

In hot weather..yes.. your high side A/C pressures will trigger the second speed on your fan..very normal..and no cause for concern. Second speed fan A/C high pressure switch kicks in usually between 210-240psi..and that is an easy high side number to get in hot weather.

The third speed is VERY LOUD and only comes on when the radiator is very hot. When the third speed fan comes on your A/C compressor will disengage as the electrical system is designed to remove the load of the compressor if the engine coolant system is that hot, when the third speed fan is on.

So..third speed fan starts blowing LOUD and your A/C system/compressor will shut down..no more cold air.

Third speed fan operation can be triggered by the A/C too. The condenser in front of the radiator can get very hot removing the heat from the cabin of the Vanagon on a very hot day. That heat is pulled into the radiator. The radiator will have a hard time shedding the heat from the engine and condenser too..then the third speed fan comes on..and your A/C stops working till the condenser cools down.

The third speed fan is not controlled by the A/C system at all..rather the third speed fan effects the A/C system when engaged by the radiator thermo fan switch.

Wed Sep 09, 2015 9:07 pm

OK. It is sounding like under east coast humid and hot temps I should not be concerned with the medium speed fan running the way it has. Thanks for the feedback. 😀