What is this part?

[wrightwc]

'87 BMW 635CSi with dual A/C (1 compressor with separate front and rear evaporators and expansion valves)

There is something looking like a valve on the suction line between the compressor and where the front and rear evaporator return (suction) lines "y" together. It has a small copper line screwed to it that leads to the front expansion valve that also has a temp probe. The rear expansion valve is electrically operated and looks like a Chrysler "H" block.

The question is, what is this part and what does it do? How does it work?



It's Ref. no. 3 in the picture of link below.
Hose 16 is the suction line to the compressor, line 4 is suction line from the front evaporator and 1&2 lead to the rear evaporator. Ref. 9 is the high side from the receiver/dryer.


http://www.realoem.com/bmw/showparts.do ... g=64&fg=60

[Warren Willingham]

Ok, I can't find it in Alldata. My thought is that it could be a refrigerant shutoff for when the rear air is turned off. That is usually in the liquid line. Your diagram calls it a voltage regulator. Your vehicle does show a refr shutoff valve but in the pic I found it's not like that. So, I'm not sure and will watch this post for someone who's worked on those. At first I thought it was a fuel cooling line like Jaguar has but I don't see any fuel lines. Unfortunately that diagram doesn't explain much. Sorry.

[Nacho]

Looks like a rear unit solenoid valve. Keeps refrigerant from flowing to the rear evaporator when is not in use

[wrightwc]

Thanks for the responses.

Well, both the front and rear suction lines "Y" into each other BEFORE the valve, so it would shut off both the front and rear units. Also, although it is called a "voltage regulator" there are no electrical connections to the valve at all (perhaps something lost in the translation?).

The rear unit does have an electric shut off in the highside line in the back, Ref. no. 4 below:

http://bmwfans.info/original/E24/Cou/63 ... l-64_0546/

Rear evaporator with expansion valve Ref. no. 6:

http://bmwfans.info/original/E24/Cou/63 ... l-64_0542/

[wrightwc]

I've been poking around on the net and I was wondering, could this valve (Ref. No. 3 in the first picture) be a "Suction throttling valve" (STV)? This is the definition I found:

"(STV) A backpressure-regualted valve on some Ford and GM systems placed between the air conditioning evaporator and compressor which controls evaporator pressure to provide maximum cooling without icing evaporator core."

Or maybe a "POA suction throttling valve:" : A term standing for "pilot operated absolute" and is a modification of a Suction Throttling Valve which has a metal bellows with a vacuum instead of a diaphragm; it provides more accurate evaporator pressure control, allowing for lower evaporator temperatures without cone icing

If so how does this kind of valve work?

[ACProf]

The last time I saw a suction throttle valve was on a 1962 Buick Special. I don't believe GM made them more than a couple years. It went in place of a TXV and worked to prevent evaporator freezeup by bleeding hot liquid from the high side directly into the evaporator.

THe POA was also a standard GM evaporator controller in the late 60's. I found one on a '69 Chevvy Impala. It had a sealed inner bellows chamber I guess with about 30psi with one end fixed to a needle valve sort of thing. Around this bellows was low side system pressure. The bellows opened/closed the valve depending on the low side pressure. The entire assembly was sealed up and attached between the high side from the condenser and the evaporator. If it worked-it worked. If it didn't you bought a new one. Nothing to adjust.

These were also on the Corvettes of this era. Might find some info about them on some corvette rebuild sites.

I kinda doubt that ref 3 is either one of those....
ACProf

[acsource]

The expansion valve on your system means there is no STV or POA.

[wrightwc]

Maybe seeing the whole system will make more sense? I used to think it was a proportioning valve of some sort until I realized that the front and rear suction lines simply "Y" together before they get to the valve. Could it be working in conjunction with what looks like a Chrysler "H" valve on the back evaporator?

(Sorry, you have to use the link below. The HTML is turned off and the BBCode won't properly display the image:)

[Warren Willingham]

I might have to retract my previous post. It looks like that could be some type of suction throttling valve. JUST A THOUGHT!! I say this because there is a liquid line running off the top which leads me to that thought. I'm open for any rejection of this. I wish I could see where that line goes. I'm talking about the small line attaching to the top of that device. It looks like some type of bleed line or equalizing tube. Maybe that line hooks to the expansion line which would be an equalizing tube and ....... well I usually don't guess but that's what I'm guessing.

[wrightwc]

.......... I wish I could see where that line goes. I'm talking about the small line attaching to the top of that device. It looks like some type of bleed line or equalizing tube. Maybe that line hooks to the expansion line which would be an equalizing tube and ....... well I usually don't guess but that's what I'm guessing.

I asked a reliable parts man who knows these cars and he replied in his eMail that it connects to the "evaporator" valve which I take to mean the expansion valve?

Would this mean that it could be a STV and if so, how would it work with the two expansion valves?

(I don't know if this will help puzzle out what the valve does, but these cars are notorious for the front to start blowing warmer vent temperatures while the back remains cold.)

[Uraijit]

This may be a long shot, but I'm thinking it's some sort of proportioning valve, which restricts overall flow when the rear air is shut off. When the valve is shut off in the rear, without the valve you're talking about, you'd still moving just as much refrigerant through half a system.

Because both sides are Y-ed into eachother for both front and rear evaporators, the pressures would be equalized, but the ammount of FLOWING refrigerant needed would be cut roughly in half. That valve should be able to cut the overall flow in half, without affecting pressures significantly.

Am I making any sense? Maybe I'm reading too much into this, but I'm on the last hour of a 10.5 hr. night shift, and my brain is running on pure caffine and sugar.

[Uraijit]

Almost positive now, I drew it out on the white board here at work, and determined that with such a system, all lines would be normal opperating range except between high side of the compressor, and the valve in question. The valve would have to allow 50% of the high-side to flow back immediately to the low-side to keep from blowing the seals (since that pressure would be at 200% normal pressure).

I determined that for my theory to work, I would need a third line coming off the valve to allow for bleed-off of that extra pressure. Came back and looked at the diagram, and what do you know, there's just such a line!

I'm 98% confident that this is what's going on here. Thoughts? Opinions? Total obliteration of my theory? Lets hear it!

[rmwmh1]

You nailed it . Took the part in question with the small copper line coming in from the firewall side off the car . Took it apart . It has a spring loaded piston with a cup ype diaphram behind it . The diaphram is actually molded onto the end of the piston . The piston has about 20 mm travel and has a 1 mm vent hole and a recessed area such that flow is modulated as pressure moves it back. The exterior portion of the device that has two screws and nut facing the front of the car is actually open to atmosphere via a small slot underneath . So as the piston is forced back against the spring pressure , air vents out while the refrigerant stays on the other side of the diaphram . Its pretty well built . Used a light smear of Hylomar sealant when putting back together . Took it apart because I had a pile of crud in the intake screen at the compressor suction so wanted to see if this device was fouled .