AC and Co0ling Fans
Racer
Joined: Aug 2004
Posts: 438
Likes: 15
From: satellite beach fl
Also want to add the I said earlier it came on high speed but got to thinking it was low speed so I went and double checked. Cold car ac on no fans on startup but a few minutes later the passenger side fan only cycles on and off on LOW speed. Sorry for the misstatement earlier.
Thread Starter
Melting Slicks
Joined: Apr 2008
Posts: 2,703
Likes: 167
From: Western Washington
Ok, I put my ac gauges on and engine cold ac on the pressure builds to about 250 psi and it cycles the passenger side fan on low (sorry about the mistake earlier) the pressure drops to about 100 psi and the fan goes off. It repeats the on off cycle.
Racer
Joined: Aug 2004
Posts: 438
Likes: 15
From: satellite beach fl
Your cutoff appears to be 120 psi low, 250 is very close to high speed command @ 255 Heres a partial of operating temps and pressures.
The only thing confusing is Run-on Temp 284, it means fans run on low after engine is stopped and key is off. And fan 1 = both fans low, fan 2 = both fans high.
Last edited by purrvert; Aug 30, 2021 at 02:25 PM. Reason: addition
Drifting
Joined: Mar 2018
Posts: 1,365
Likes: 414
From: New Jersey
That's a pretty nice validation of the AC pressures affecting fan operation. If all the relays and wiring are working there is not a low speed operation of only one fan.
Racer
Joined: Aug 2004
Posts: 438
Likes: 15
From: satellite beach fl
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Thread Starter
Melting Slicks
Joined: Apr 2008
Posts: 2,703
Likes: 167
From: Western Washington
I let the car run and as it warmed up the AC psi stabilized and both fans came on. Is there a sensor that might be the reason the fans don't come on at startup? Also when I turn the AC off before shutting off the engine it will be on when it is started again, is it possessed???
Racer
Joined: Aug 2004
Posts: 438
Likes: 15
From: satellite beach fl
I let the car run and as it warmed up the AC psi stabilized and both fans came on. Is there a sensor that might be the reason the fans don't come on at startup? Also when I turn the AC off before shutting off the engine it will be on when it is started again, is it possessed???
I'm a little confused are your fan running low or high? If your fans are running low that means relay 45 is working, relay 44 is mechanicaly correct and relay 43 is not involved. If fans are on high all three relays are functioning. Also there no possibility of one fan running low.
Racer
Joined: Aug 2004
Posts: 438
Likes: 15
From: satellite beach fl
Thread Starter
Melting Slicks
Joined: Apr 2008
Posts: 2,703
Likes: 167
From: Western Washington
I think perhaps trying to see the driver side fan from above it didn't look like it was running but it was. I got the car up in the air to make sure and both are running on low. Pressures started at 34 psi and high side builds to just over 250 psi and both low fans kick in dropping the high side down around 150 psi. At idle as the car warms up the fans stay on and the psi level off at 36 and 235 but when speed increased to between 1200 and 1500 rpm the low side goes to about 40 and the high side increases to over 300 psi and the high speed fans kick in and drop it back to about 150 psi. Car was 196 degrees and of course under hood was quite hot (at least 120 by the thermometer placed there). Is this normal?
Last edited by narlee; Aug 31, 2021 at 12:06 AM.
Racer
Joined: Aug 2004
Posts: 438
Likes: 15
From: satellite beach fl
I think perhaps trying to see the driver side fan from above it didn't look like it was running but it was. I got the car up in the air to make sure and both are running on low. Pressures started at 34 psi and high side builds to just over 250 psi and both low fans kick in dropping the high side down around 150 psi. At idle as the car warms up the fans stay on and the psi level off at 36 and 235 but when speed increased to between 1200 and 1500 rpm the low side goes to about 40 and the high side increases to over 300 psi and the high speed fans kick in and drop it back to about 150 psi. Car was 196 degrees and of course under hood was quite hot (at least 120 by the thermometer placed there). Is this normal?
Drifting
Joined: Mar 2018
Posts: 1,365
Likes: 414
From: New Jersey
There is no sensor for a/c-fan start. It's a common misconception. When car is at 80-90 deg at startup and condenser pressure is climbing from 80-90 psi for what reason would you need cooling fan?
I'm a little confused are your fan running low or high? If your fans are running low that means relay 45 is working, relay 44 is mechanicaly correct and relay 43 is not involved. If fans are on high all three relays are functioning. Also there no possibility of one fan running low.
I'm a little confused are your fan running low or high? If your fans are running low that means relay 45 is working, relay 44 is mechanicaly correct and relay 43 is not involved. If fans are on high all three relays are functioning. Also there no possibility of one fan running low.
Racer
Joined: Aug 2004
Posts: 438
Likes: 15
From: satellite beach fl
The cooling fan limits or lowers the high side pressure since with no airflow over the condenser the high side pressure can become too high. I believe this a heavy load on the ac compressor that could damage something if the pressure gets too high. It also can cause a rough idle if the fans don't come on with the compressor due to the increased load.
Please answer; When car is at 80-90 deg at startup and condenser pressure is climbing from 80-90 psi for what reason would you need cooling fan?
Last edited by purrvert; Sep 1, 2021 at 02:32 PM.
Moderator, Tech Contributor
Joined: Sep 2013
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From: Cape Coral, Florida
The cooling fan limits or lowers the high side pressure since with no airflow over the condenser the high side pressure can become too high. I believe this a heavy load on the ac compressor that could damage something if the pressure gets too high. It also can cause a rough idle if the fans don't come on with the compressor due to the increased load.
Last edited by C5 Diag; Sep 1, 2021 at 02:38 PM.