1987 635CSi A/C Problem

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bardone

1987 635CSi A/C Problem

Post by bardone »

This car has dual A/C.
A/C works great thru rear air vents, but poor thru front vents.
Does this system have two separate evaporators? Or one for the front, in the dash, and another for the rear, inside the rear console?
Or can there be another problem?
Thanks.
Chris Wright

Re: 1987 635CSi A/C Problem

Post by Chris Wright »

bardone wrote:A/C works great thru rear air vents, but poor thru front vents.
Poor as in "Luke warm" air, or poor as in low air flow?
Does this system have two separate evaporators? Or one for the front, in the dash, and another for the rear, inside the rear console?
Yes, 2 evaporators, and 3 separate blower motors! One for the heater/fresh air blower, a separate blower for the front A/C and one for the rear A/C.

This is a classic symptom of the system NOT having a full charge. The rear expansion valve seems to get priority and hogs all of the refrigerant, while the front valve will close down to help keep the total system pressure balanced.

But more on that in a minute, first, keep all of the upper vent thumb wheels closed, and then move all three sliders closed, to the left. When you move the center slider back and forth (pause between movements), you should hear the Fresh Air Flapper Door open and close. The early cars are cable operated, but the later cars have a pot in the center slider that sends a signal to a controller that in turn operates an electric stepper motor to position the Fresh Air Flapper Door. this is to allow the A/C to over ride the current position and close this door automatically when the A/C is turned on to prevent hot outside air from coming in to dilute the A/C. Return the center slider to the closed (left) position and make sure you hear it move closed, or you are just blowing the A/C out the heater blower.

With the interior cooled down, turn the rear temperature control to full hot, so that the rear stops cooling, shut off the rear blower, turn the front A/C to full cold and see if the front gets cooler. If so, the charge is probably low and won't operate both evaporators at the same time.

The dual system takes more refrigerant than the single system. The correct amount can be found on a sticker in the middle of the hood at the bottom when it is open.

<a><img src="http://bigcoupe.com/ims/pic.php?u=21GvpX2&i=346" border="0"></a>

<a><img src="http://bigcoupe.com/ims/pic.php?u=21GvpX2&i=227" border="0"></a>
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Last edited by Chris Wright on Fri Aug 30, 2013 4:56 pm, edited 1 time in total.
Jon Ackermann

Post by Jon Ackermann »

Chris:

Do we need to replace both front and rear receiver-driers when re-doing/upgrading to 134a.

I ordered the retro-kit from the BMW dealer and it only came with the front reciever-dryer.

Thanks.

Jon
Chris Wright

Post by Chris Wright »

Jon Ackermann wrote:Chris:

Do we need to replace both front and rear receiver-driers when re-doing/upgrading to 134a.

I ordered the retro-kit from the BMW dealer and it only came with the front reciever-dryer.

Thanks.

Jon
I'm no expert, but as far as I know there is only the one receiver/dryer at the front.

The "tank" (Ref #5) at the back is listed as a "Pipe" and is one piece with the hose. I don't know if it is a filter (if so, why wouldn't it be replaceable, i.e. separate from the hose?) or maybe it is an expansion tank to take the shock of the electric valve (Ref #4) closing or perhaps a muffler to dampen the noise as the valve cycles on and off?
____

I'm curious, what came in the retrofit kit?

Was it worth the money, or could you assemble the separate parts cheaper from the usual suspects?
Jon Ackermann

Post by Jon Ackermann »

Chris:

The retro kit came with the receiver-drier, 5 o-rings and two drier knobs.

The price is slightly less as a kit vs buying seperately.

I also needed to order seperately the front and rear expansion valves and additional o-rings.

I will be taking it to the BMW dealer sometime soon, so I will let you know how everything works out and what I think of the 134a vs r12.

Thanks.

Jon
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Re: 1987 635CSi A/C Problem

Post by RTHLSS1 »

Hi guys,

I had my AC refilled today. It blows nice and cold out of dash vents but when I tried it in back "fridge" it blows warm air.
Any suggestions what could be wrong?
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Re: 1987 635CSi A/C Problem

Post by 635sharknose »

Front and rear are 2 separate systems, with their own expansion valve and evaporator. There may be something wrong with your expansion valve. It is also possible that the hot/cold control is not working.
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