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What should air temp be from vents with the AC on?

 
Old 07-10-2010, 08:30 PM
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code7rpd
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Default What should air temp be from vents with the AC on?

I had my 90 C4's AC charged a few months ago with R134 and it blows cold but not super cold. I checked the temps and it reads 62 degrees with the car idling in about 90 degree weather. Shouldn't it be lower? The condenser fan is running when the AC is on.

I also noticed that the center vents do not seem to blow very hard - could it be the fan blowers are going out?

Any help would be appreciated - thanks!
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Old 07-10-2010, 11:03 PM
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Bugeye
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I recently had mine retrofitted to R134, and it tested at 38 degrees Fahrenheit after. Sounds like something is not right with yours.
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Old 07-11-2010, 10:45 AM
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According to the graph in "Without Guesswork" at 90 degrees ambient the center vent temperature should be between approximately 44 to 52 degrees.
Be sure to measure center vent temperature with the ventilation system set on recirculation. Run the car for 10 minutes at 2000 rpm before testing. If it's still not within spec, find a a/c service that can properly charge a 964 system and have them check it out. It's also possible that you have mixing servos that aren't adjusted right or aren't operating. A Bosch Hammer should pinpoint any faults.
Make sure that you don't have air blowing on the floor and to the windshield when you set the sliders to blow out through the center vent. If you do, one or more servos may not be operating. Once again, a Bosch Hammer car pinpoint any problems with this.
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Old 07-11-2010, 04:26 PM
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Thanks Paul - let me try it again. I have a Hammer and did not even think about using it but that would definitely be a good start. I did notice that last night with an ambient temp of 72 degrees I was pushing 46 degrees through the vents but let me recheck after running the car at 2000 rpm for 10 minutes. I have a pressure gauge but have been reluctant to use it as I am not really certain what the pressures should be.
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Old 07-11-2010, 05:59 PM
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Bug,
Would you mind sharing what the cost of the retrofit was?

To use R12, I was quoted ~$400 for just the freon.
Best,
John

Originally Posted by Bugeye View Post
I recently had mine retrofitted to R134, and it tested at 38 degrees Fahrenheit after. Sounds like something is not right with yours.
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Old 07-12-2010, 12:40 AM
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The parts, not includng the dryer, are about $10; the dryer is about another $125 plus labor to install it 0 about an hour. The additional cost fo charging can vary but generally runs about $100 to $150 so your estimate is not far off if the dryer is included.
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Old 07-12-2010, 08:14 AM
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Vent temperature is compllicated. Outside ambient, inside ambient, and inside humidity affect the temperature. Engine speed affects it. Air flow around the condensor coil affects it.

I found cleaning the condensor lowered the vent temperature by several degrees. If your compressor is tired, you will see colder temperature when running and warmer temperature at idle. Having enough freon is important, but it is not as critical as it sounds. There is an accumulator to hold the excess, so as long as you have enough to keep some at the bottom of the accumulator, adding freon does not help.
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Old 07-12-2010, 09:44 AM
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Originally Posted by springer3 View Post
Vent temperature is complicated. Outside ambient, inside ambient, and inside humidity affect the temperature. Engine speed affects it. Air flow around the condensor coil affects it.

I found cleaning the condensor lowered the vent temperature by several degrees. If your compressor is tired, you will see colder temperature when running and warmer temperature at idle. Having enough freon is important, but it is not as critical as it sounds. There is an accumulator to hold the excess, so as long as you have enough to keep some at the bottom of the accumulator, adding freon does not help.
Good points but too little or too much R-134a (out of spec) will have a big affect on vent temperature. If you do a search you will find those who couldn't achieve good vent temperatures due to improper charging.
Code, 46 degrees at 72 degrees ambient is in spec to the low side (colder is better). If you want to take a crack at checking low and high side pressures you will need the charts because those pressures will vary depending on ambient temperature.
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Old 07-12-2010, 12:07 PM
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See my post in this thread for vent temps. This is from the service manual.

https://rennlist.com/forums/964-foru...ight=vent+temp
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Old 07-12-2010, 06:13 PM
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I paid $245 total parts and labor. I believe the hoses were all fine and it was essentially the 134 Retro Valve Kit plus change to R134 (including freon plus oil for the a/c system). Works great so far, and have used it for a couple long rides.
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Old 07-12-2010, 06:44 PM
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Definitely good points from all - let me do some checking and report back.
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Old 07-13-2010, 02:25 PM
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I did not have a chance to do more than hook up the Bosch Hammer and was surprised by the 6 error codes that were stored. I got errors such as: Rear blower motor seized, rear blower motor no signal, condenser fan seized, front flap motor signal implausible, interior sensor malfunction, and a few others. I know that neither the condenser fan or the rear blower motor are seized as the work and I had the CCU, which I bought used, checked out to make sure it was working before installing it - I sent it to Ottos of Venice and they gave it a good bill of health so I am sure that it is in good working condition.

What else could cause so many errors? I cleared them and will check again this weekend to see if they reappear.
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