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Why is my expansion valve wrapped in foam rubber?

MiataPete on Fri May 24, 2013 4:49 PM User is offline

Year: 2001
Make: Mazda
Model: Miata
Engine Size: 1.8L
Refrigerant Type: 134a
Country of Origin: United States

The thermal expansion valve, which is internal to the box containing my evaporator, is wrapped in an elastic foam rubber. The expansion valve is directly in line to the flow of air from the heater/AC fan. Why is this valve wrapped? Should it be?

I have 2 jpg's I could attach that show this ... but, I can't figure out how, or if, I can attach pictures.

OK ... figured it out ... I have attached the 2 jpg's showing the wrapped valve.






Edited: Sat May 25, 2013 at 1:46 AM by MiataPete

94RX-7 on Fri May 24, 2013 5:05 PM User is offline

You're talking about the valve itself, and not the sensing bulb, right?

Is the expansion valve positioned such that any condensate that forms on it will be caught by the "drip tray" that funnels condensate out of the car? If not, then they've wrapped it to prevent condensate from building up on it, and dripping in an area where it shouldn't be. If it is over the "drip tray" then I have no idea.

WyrTwister on Fri May 24, 2013 6:54 PM User is offlineView users profile

Wouldn't the " down stream " side of the expansion valve be very cold ? I would guess the foam is insulation ( as some one has said ) to cut down on condensation , at that point ?

I have not worked on an expansion valve since my youth .

God bless
Wyr

MiataPete on Fri May 24, 2013 6:55 PM User is offline

Right ... the expansion valve is wrapped. The temp sensing bulb, on the other side of the evap, is open to the airflow being directed into the car.

And, yes again, if the expansion valve gathers moisture, that moisture will drop directly to the bottom of the box, and flow directly out via the drip hose.

I'm puzzled, too. Shouldn't the expansion valve be able to sense the temp of the incoming air from the fan?

Thanks for the reply.
Pete

MiataPete on Fri May 24, 2013 7:01 PM User is offline

Right, the downstream side will be very cold (hopefully ... if I don't screw up).

But, this valve is on the "warm" side of the evap ... though, obviously, both the input line and the output line from the evaporator both travel through the valve. So, the valve is touching refrigerant lines of two temperatures.

Pete

TRB on Fri May 24, 2013 7:09 PM User is offlineView users profile

Valve gets wrapped to the fitting. Bulb gets wrapped to provide proper temp reading for the superheat.

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94RX-7 on Sat May 25, 2013 8:38 AM User is offline

Quote
Originally posted by: MiataPete
Right ... the expansion valve is wrapped. The temp sensing bulb, on the other side of the evap, is open to the airflow being directed into the car.



And, yes again, if the expansion valve gathers moisture, that moisture will drop directly to the bottom of the box, and flow directly out via the drip hose.



I'm puzzled, too. Shouldn't the expansion valve be able to sense the temp of the incoming air from the fan?


That appears to be a block type expansion valve. It has no sensing bulb. The thing you're talking about on the other side of the evaporator is probably a thermistor so that the control electronics can determine evaporator temperature.

The expansion valve doesn't care one whit about the air temperature. All it cares about is the temperature of the gaseous refrigerant leaving the evaporator core so it can control how much liquid it is allowing into the core.

MiataPete on Sat May 25, 2013 4:51 PM User is offline

Yes, it is a block type valve, and the temp sensor on the other side of the evap does send a signal to the PCM, to control the compressor clutch ... I figured that out, when trying to test that sensor, and having to examine the factory wiring diagram for the car.

Just this morning, at Harbor Freight (one of my favorite places in the world), I ran into a guy who works on AC systems. He said that the foam rubber wrap is common on expansion valves, and my valve should remain wrapped (my new valve .... I am buying one from Mazda).

He said that the wrap helps to maintain a constant temperature in the valve, to help avoid freezing of the internal components in the valve, during on/off cycling.

Thanks for the input ... I definitely needed help on this one.

Pete

94RX-7 on Sun May 26, 2013 9:39 AM User is offline

Quote
Originally posted by: MiataPete

Just this morning, at Harbor Freight (one of my favorite places in the world), I ran into a guy who works on AC systems. He said that the foam rubber wrap is common on expansion valves, and my valve should remain wrapped (my new valve .... I am buying one from Mazda).



He said that the wrap helps to maintain a constant temperature in the valve, to help avoid freezing of the internal components in the valve, during on/off cycling.


I just wonder why Mazda did it on this car and not on the RX-7 which also uses a block type valve in the same type of configuration (and a right angle type valve in cars with another brand of A/C system). Maybe they were trying to improve system efficiency? Who knows.

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