Bad expansion valve symptoms?
 

Anyone ever see a bad epansion valve/ symptoms?
I just did some homework on the pressures and temps according to the MB cd and mine are off with correct amount of freon. 91 300E with R-12 that was just evacuated, flushed and recharged at an MB independent shop.

MB spec: Ambient 104 F / 40% Relative Humidity, High Blower Speed=
Low side 29-36 psi High side 377-391 psi Duct temp 55-60F.

Actual readings 105 ambient/ 25% RH, Low side 45-47psi High side 220-235 psi and 80-83F duct temp. That is with the front fans on high and helper fan.
Noticed last night that the guages will slowly fluctuate about 10 to 20 psi. the high side will go up 20 while the low goes down 8 or 10 at the same time, then they go the other way and over and over but like 3 or 4 times a minute.
This morning it was 86F ambient 38% RH on the way to work and on low it only blew 65F....same as when it was 105F yesterday. So Im wondering if the expansion valve is limiting the freon to the evap to 65F on low blower or any blower for that matter , or if the evap is dirty and clogged on the outside, but it blows hard.

normally, I wouldn't throw money at a situation....but an expansion valve costs next to nothing...if you can have someone evacuate and recharge....

just make sure you replace the o-rings.... common leakage problem at the expansion valve....

i think the part is about 30 dollars.

Yeah, its $21.02 for the valve. Hell, only another $50 for the R-Dryer.
Lucky for me this place is in PHX.
www.***************

with all due respect to Fast Lane... I have used ********az for a majority of my needs... they are incredibly inexpensive

That doesn't really look like a bad expansion valve to me although it could be partially open causing such pressures.

It looks to me more like a weak compressor. Niether one of these scenarios would be very common at all. The only thing that usually happens to the TXV is that it leaks on top at the diaphragm. The compressors usually work or they have catastrophically failed.

I have had a similar expansion valve fail open on another make car and it gave hardly any difference in pressure at all. When they fail in function, I think it is more common for them to pinch off and actually draw the low side into a vacuum.

Hope this helps somehow,

Hmmmm, well I know that if I turn off the fans the high side will go right up to 450 or so, so I know the compressor can compress. Im just about ready to say screw it and replace the valve........after I have a look at the evap surface.

did anyone every put any kind of stop leak in there? that could gunk up a few things including the expansion valve over time.

if anyone put any sealer in it either prepare for a very expensive replacement of everything or get used to driving with the windows down.

It was just evacuated, lines taken off compressor, condensor and evap and lines flushed, then put back together. The only thing that makes sense to me is either the expansion valve metering of the freon is "out of spec but kinda working" or the evap has crap all over it. But if it were the evap, the outlet would be ice cold since the air couldnt get to it, but its warm/ cool. And the pressure would be much lower. I have pinched off the heater water and checked all pods with dash off.
I think the valve is open too much flooding the evap causing higher pressures and less cooling/evaporating of the freon and causing low high side pressures cause its just blowing through the evap.
Like running a car with no thermostat/metering device. It can overheat due to the coolant going through the radiator too quick to let the air cool it.
Maybe Ill just go out and buy a corvette. :usa:

It appears that the refrigeration system is cooling properly.

Remove the glovebox and check the top two vacuum lines on the switchover valve to see if they are leaking. These go to the vac pods that control the fresh air door. When the fresh air door is open when it should not be, vent temps as you describe will be the result. BTDT.

Good luck,

I actually ran the A/C with the dash removed the other day. I checked the recirc door and all other pods, all were good. I ordered a new expansion valve and orings last night for $24.00 new. I am sure this is the problem now. I have spent days reading over 50 articles on freon, A/C systems, pressures, etc. This morning at 88F ambient on low blower, its got down to 52F vent temp cruising at 70 mph. I looked away for 20 sec. and suddenly it was back at 61F on the freeway. I will be changing it out on monday. I will post the results for sure. :rolleyes:

The more I look at this, the more I think that it MIGHT be the TXV. Just because this is not usually how TXV's fail, does not mean that one cannot fail this way.

If you can recover the refrigerant, replacing the TXV won't be too big of a deal. I replaced mine a few months ago and the only problem is that it is just hard to get at.

Good luck,

Ok, Now I am really pissed off :madani:
Last night I replaced the TXV with a new one, and use my last 3 cans of R-12. 2X 14 oz. and 1x 12 oz.
The f*&#ing thing is doing the same thing.
Ambient 98F, 2000rpm, Low blower speed = duct temp 60
High side 180 , low side 34 .......low line semi cold

High blower speed = 75F
High side 195, low side 51 low line warm

Took out the blower motor.
Stuck a thermometer in the evap.
Ran the a/c with no blower.
Evap temp got to 25F and falling, low side 20, high side 165 and whole low side line frosted ice........so I shut it off as not to do any damage.
Sprayed the evap down with lime-away and rinsed, then with soap and water and high pressure water.
Put it back together........still only 60F.
I almost got 5 gallons of gas and a flare......bit I will not be beat at my own game. Anyone know a MB tech that may have seen this or know something I dont? I am getting an auto trader at lunch just in case. :bigcry:

have you checked the heater control valve? if it's leaking, hot water is coming in to the heater core all the time and the a/c is fighting it. that might expl the cold evap temp but warm air. to test you could bypass it for the time being.

What is the eyesight showing ??????