Not sure what the problem is 9or even if there is one)

WindyCityGuy on Sun April 10, 2011 7:55 PM

Year: 1980
Make: Mercedes
Model: 280SE
Engine Size: 2.8
Refrigerant Type: R-12
Ambient Temp: 86
Pressure Low: 25
Pressure High: 175
Country of Origin: United States

I have a 1980 Mercedes 280SE. The car has a Sanden compressor, aluminum parallel flow condenser, a new set of barrier hoses, and a new expansion valve. It's filled with R-12.

At 86* ambient with the engine running @1500 rpm, the aux fan on and an additional fan in front of the car I am getting air out the vents right about 50* (25 low/ 175 high). It seems like it should be colder, plus the evap temp switch never cuts the compressor - it's set for 37 degrees. I thought the evap temp switch was bad so I pulled the dash and put an electronic temperature sensor right against the evap coil - it was reading around 50*. Here's the kicker (and the part I don't understand) - I put another temperature sensor on the suction fitting at the compressor and it was reading 33-35*.

The only way I could get the evap temp to cycle was to pull the plug for the cabin fan and let the evap core chill down.

Should the evap be colder than 50*? I get that the suction fitting will be colder than the evap core but should it be that much colder?

Also, does the low side pressure look high?

Thanks in advance for any insight.

WindyCityGuy on Mon April 11, 2011 7:30 PM

Ok, I'll sweeten the pot. I'll make a $25 donation to the ACkits.com forum if someone can help me fix this issue.

Cussboy on Tue April 12, 2011 2:44 PM

I think the evaporator should get to the mid 30s and then its thermostatic deicer switch should shut off the compressor (that's what my 1988 R-12 truck AC does). From your pressures, I'd think you might be a little low on refrigerant.

JACK ADAMS on Tue April 12, 2011 4:29 PM

First off, check your hot water flow. You can pinch off the heater hoses to make sure the blend door is shutting all the way. Also check the fresh/recirculation air door to make sure it is working properly. Also with the system being modified the refrigerant levels will be a guess. But the sight glass in the drier should give you a clue on being full. Hope this helps and good luck!!

WindyCityGuy on Tue April 12, 2011 9:14 PM

Jack - my heater line has a ball valve in it to positively stop the hot water in the summer. I verified the heater core and metal pipes to it were still cool. Good thought - that's why I put the ball valve in.

It's too cold right now (low 50's) to test it but I'm wondering if the expansion valve is bad (again). When it warms up again I'll recheck.

WindyCityGuy on Wed April 13, 2011 7:07 PM

It was about 70* today and I had time for a quick test. I started the car and let it run for 10 minutes until the air coming out the center vent stabilized around 50*. I pulled the expansion valve temp sensing bulb off the exit line from the evap and dunked it in a cup of water @ 125*. The vent temp stayed the same. I put it in a cup of ice water and the vent temp stayed the same.

Is this indicative of a bad expansion valve or is the ambient too cool to draw any positive conclusions?

JACK ADAMS on Wed April 13, 2011 7:31 PM

I think it will be best to wait till you have a good 75-80* day for a true test. be sure to post the gauge readings as well as your vent temps. Also did you check your Fresh/Re-Circulation door to make sure it is working?