I did some experimenting with my Old Air unit. I attached two wires, one to
each side of the "safety switch" which combines high and low pressure functions
into one switch. 30lb. low pressure cutoff, 380 lb. high pressure cutoff. I
ran the two wires back into the cab, attached a 12V LED to each wire and
grounded the LEDs. This way one LED lights anytime the thermostat switch
buried in the evaporator tells the compressor to kicks in and the other LED
should be on when the thermostat wants the compressor kicked in and pressure is
between 30 and 380 PSI. I also stuck a thermometer into the air outlet duct in
the middle of my dash, about 18" of flex duct away from the air outlet on the
evaporator case.
For you AC experts, my compressor is a Sanden SD5H11 which is the R-134A
version of the Sanden SD-507, a 5 cylinder, 6.7 cubic inch displacement model.
Here is a pointer to Sanden's service manual:
http://www.sanden.com/support/servicemanual/english/table_of_contents.html
My truck uses a condenser that is about 19" wide, 16" tall and 1.25" thick. It
is mounted within 1/4" of the front of the radiator. The only fan is an 18" 5
blade engine driven fan and there is a very tight fitting shroud surrounding
the fan and attaching to the radiator mounting brackets. The engine has a 180F
thermostat and only exceeds that by 10F on very hot days.
Yesterday afternoon it was about 85F outside. I turned on the A/C and watched
the LEDs and the thermometer. I never saw the LED attached to clutch side of
the safety switch off when the other side was on, signifying that the pressure
was always within limits.
I tested at extended idle time, low speed (about 1000 RPM which is just under
30 MPH) and high speed (2100 RPM @ 60 MPH).
The outlet air temp dropped slowly to about 40F a few minutes after turning the
AC on. It stayed at 40-41F for a few minutes until the thermostat kick out.
The temp drifted back to about 43F, the thermostat kicked in again and the
whole cycle repeated. At highway speed the exit air was about 1 degree warmer.
I didn't measure time on vs. time off, but I'd estimate it as about equal,
maybe 30-45 seconds each. I also think that the faster I go the shorter the
"off" time. Probably because the hot air outside blasting against the sheet
metal transfers heat better at high speed.
The thermometer I was using is a 3" dial with a 6" long probe, designed for AC
service work. I service guy left it behind at my house years ago and never
returned to get it.
Did the Old Air guys ever respond to you? I never heard from them.
-----Original Message-----
From: Wayne Roworth [mailto:wroworth@hotmail.com]
Sent: Monday, May 19, 2003 2:59 PM
To: oletrucks list
Subject: [oletrucks] a/c cold to warm
Just finished installing my "Old Air Products" a/c. I had it checked and
charged by a so-called "expert". It's weird but it's icy cold at idle and luke
warm when traveling down the road. I have only experienced the opposite due to
low compressor rotation at idle. Had it checked again, by the same guy, and no
leaks etc. The belt is not "rock tight" but it's not slack either. Any ideas?
Wayne - '47 Panel - http://www.itswhatsnext.com/ifs%20project.htm
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
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