fan operation questions
Thread Starter
Burning Brakes
Joined: Aug 2002
Posts: 926
Likes: 2
From: chandler az
fan operation questions
Does someone have the schematic for the fans on a 99 coupe?
My buddies 99 with the AC on max it seems like only 1 fan is running.
The temp out the vents is just cool not cold. I know the issue is partially fan related because spraying the condensor with water drops the vent temps.
on a side note - what are the typical pressures for this system. IT is 90 deg f. outside at idle with the fans like they are I am seeing 80psi on the low side and 125 on the high side. On a regular system that doesn't have a variable displacement compressor like ours I would say that is out of whack.
I can jump the relays and get the fans to go into High mode.
With the AC on shouldn't they both be on HIGH?
My buddies 99 with the AC on max it seems like only 1 fan is running.
The temp out the vents is just cool not cold. I know the issue is partially fan related because spraying the condensor with water drops the vent temps.
on a side note - what are the typical pressures for this system. IT is 90 deg f. outside at idle with the fans like they are I am seeing 80psi on the low side and 125 on the high side. On a regular system that doesn't have a variable displacement compressor like ours I would say that is out of whack.
I can jump the relays and get the fans to go into High mode.
With the AC on shouldn't they both be on HIGH?
Pro
Joined: Jun 2007
Posts: 631
Likes: 3
From: Joppa AL
I'll have to leave your fan questions to the experts but I'll take a go at your side note. Here is a link to a chart that shows AC pressures based on humidity, temp and RPM. http://forums.corvetteforum.com/show...ghlight=AC+101
As you can see, your pressures are way off. You should be in the 35/300 area. With a low side of 80 I'm surprised you're getting any cooling at all. In a 134 system evap temp closely follows low side pressure, i.e. 80 psi will produce an evap temp of about 80 degrees. With your gage readings I'd be bad suspicious of the compressor. There are other possibilities but that would be the most likely culprit. Let us know what you find. HTH
As you can see, your pressures are way off. You should be in the 35/300 area. With a low side of 80 I'm surprised you're getting any cooling at all. In a 134 system evap temp closely follows low side pressure, i.e. 80 psi will produce an evap temp of about 80 degrees. With your gage readings I'd be bad suspicious of the compressor. There are other possibilities but that would be the most likely culprit. Let us know what you find. HTH
Thread Starter
Burning Brakes
Joined: Aug 2002
Posts: 926
Likes: 2
From: chandler az
that was my understanding also from everything I have read. He did tell me that shortly after we talked he did a full throttle romp and as soon as the RPM came back down the AC started working correctly again. I wonder some valve is hanging up in the compressor.
Racer
Joined: Mar 2003
Posts: 440
Likes: 7
From: Willow Park Texas
The way the fans are set up is through 3 relays. Low runs 12v in series through both fans. Thus they come on at 1/2 speed, but both fans should be running. High speed 2 other relays kick in and it puts 12v to each fan, thus you have high speed on both fans.
If only 1 fans is running you might just swap the plugs on the fans to see if that fan is just dead. If the dead one starts running and the other one quits, it is one of the 3 relays.
At high rpm's, the PCM cuts off the compressor. I beleive that it does that at 100% throttle position or above 4000 rpm.
Reb
If only 1 fans is running you might just swap the plugs on the fans to see if that fan is just dead. If the dead one starts running and the other one quits, it is one of the 3 relays.
At high rpm's, the PCM cuts off the compressor. I beleive that it does that at 100% throttle position or above 4000 rpm.
Reb
