Cooling fan operation with a/c on
06-18-2012, 12:04 AM
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Heel & Toe
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Cooling fan operation with a/c on
I've done several searches but can't find a post with my question being answered. I noticed my car getting warmer than usual with the ac on today and found that fans are only running on low when the ac is on. I read in one post that the fans run constantly on high when the ac system is on. Is this correct? I replaced all three relays with no change. The fans will switch to high when the temp gets to 235. Also checked and found that both fans come on low speed when the ac is turned on when coolant temps are under 217. Any help our info would be appreciated.
06-18-2012, 07:46 AM
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Thanks for the info, but I found where you had made this post a few years ago. You say with the a/c on the fans go on high at 194, but mine run only on low until 235.
"If you have only one fan running then you have a problem that needs to be diagnosed. When the fans run both run at the same time at either high speed or low speed.
With the AC on the fans (both) come on at low speed at 185 degrees. They both go to high speed at 194 degrees.
With NO AC running the fans come on at low speed when the coolant reaches 226 degrees. The both go to high speed at 235 degrees.
When the vehicle speed reaches 35mph the fans go OFF no matter what the coolant temp is. Air flow through the radiator is better with the fans freewheeling than with them running.
Hopefully ByronHunter will post the wiring diagram that can help you troubleshoot what may be happening. There are 3 relays involved in the fan operation. One or more may have failed or the fan that runs only on occassion may be worn out. "
"If you have only one fan running then you have a problem that needs to be diagnosed. When the fans run both run at the same time at either high speed or low speed.
With the AC on the fans (both) come on at low speed at 185 degrees. They both go to high speed at 194 degrees.
With NO AC running the fans come on at low speed when the coolant reaches 226 degrees. The both go to high speed at 235 degrees.
When the vehicle speed reaches 35mph the fans go OFF no matter what the coolant temp is. Air flow through the radiator is better with the fans freewheeling than with them running.
Hopefully ByronHunter will post the wiring diagram that can help you troubleshoot what may be happening. There are 3 relays involved in the fan operation. One or more may have failed or the fan that runs only on occassion may be worn out. "
Last edited by 2broke2gofast; 06-18-2012 at 08:00 AM.
06-18-2012, 10:36 AM
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If you give me the lnk to that post I will correct it. It was based on information I had read on the Forum and that was wrong. The correct info is that with AC on and factory turn on temps still set the fans will not go to high speed until the coolant temp reaches the high speed turn on temp which is 235 degrees. I determined by checking as you did that the fans actually remain in low speed until the 235 factory set temp. I have not observed what happens if the turn on temp is reduced but I suspect the fans go to high speed at the lowered temp
06-18-2012, 11:01 AM
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The reason I was concerned at all was the fact that yesterday in the garage, I went to get in the car after it had sat for about 5 min to leave again. Since I was in the garage, when I turned the a/c on I noticed the fans kicked on high for about 20 seconds then went back to low and the temp showed to be only 226*. Could this be due to a pressure spike in the a/c system on startup?
06-18-2012, 12:11 PM
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If the car isnt overheating then i wouldnt stress too much about it. When my car was stock and still had the stock t stat, it would always be a lil hotter with the a/c on than with out. Plus havbe you cleaned your radiator? Our cars are bottom feeders and over time, these radiators start to collect more gunk than you think.
06-18-2012, 12:40 PM
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When you turn off a hot car and the fans do not keep running as on some foreign cars, there is a heat sink condition that occurs when the heat in the engine block is greater than the coolant temp. This causes the coolant temp in the block to increase for a short period of time until air cooling is able to reduce the overall temp (both engine block and coolant in the engine block). When you got in the car after 5 minutes it is likely that the coolant temp in the engine was greater than 235. That would have resulted in the fans coming on at high speed until the coolant temp in the engine dropped below 226. Coolant temp of solution in the radiator was very likely below 220 degrees. So when you started the car, the fans came on at high speed and ran trying to reduce coolant temp in the engine. The cooler water in the radiator would have been circulated into the engine attempting to bring that temp down. As soon as it got below the turn off temp for the high speed fan operation, the fans reverted to low speed operation.
At that point it is a moot point whether the AC is on or not. Engine temp was the overriding factor since it was above the turn on temp for the high speed fan operation (235) and above the turn temp for the fans in normal low speed operation (226). What the AC being on would accomplish is retaining the low speed fan operation once the coolant temp went below the non AC turn off temp of 219. Complex but it all makes sense once you think about it.
At that point it is a moot point whether the AC is on or not. Engine temp was the overriding factor since it was above the turn on temp for the high speed fan operation (235) and above the turn temp for the fans in normal low speed operation (226). What the AC being on would accomplish is retaining the low speed fan operation once the coolant temp went below the non AC turn off temp of 219. Complex but it all makes sense once you think about it.
Def makes sense, but I went out on lunch and started the car up and turned the a/c and after about 10 seconds the hi speed fans came on for about 25 sec and the coolant temp showing 152*. After that the fans stayed on low speed. I've read that the a/c system pressure also plays a role in fan speed control.
06-18-2012, 02:03 PM
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Interesting observation. Worth reading the section about the AC in the shop manual. I'll do that later today to see if there is additional info.
Perhaps I'll reread the cooling section again but I don't remember seeing any details related to AC other than the fans come on at 185 when the AC is on.
Perhaps I'll reread the cooling section again but I don't remember seeing any details related to AC other than the fans come on at 185 when the AC is on.
06-19-2012, 10:05 AM
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You sure it was the coolant fans going to high speed and not something else (AIR pump maybe)? I've never observed that happening or read about it happening before.