Date:         Sun, 20 Jun 2010 22:07:40 -0700
Reply-To:     Keith Hughes <keithahughes@Q.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Keith Hughes <keithahughes@Q.COM>
Subject:      Re: A/C Shuts Off over 55mph
In-Reply-To:  <BAY0-PAMC2-F7TQbmxK0001fae6@bay0-pamc2-f7.Bay0.hotmail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

> Date:    Sun, 20 Jun 2010 22:42:09 -0400
> From:    John Van't Slot<jvantslot@GMAIL.COM>
> Subject: A/C Shuts Off over 55mph
>
> I have two symptoms with my AC ('84 westy with 2.1L).
>
> 1) AC (not fans) shuts off when the motor is taxed (over 55mph). Any ideas
> why this happens? Not by design I hope.
>
> 2) I have used a couple different pressure gauges (that come with the
> refrigerant cans) and they show the high side around 65-70 (regardless of
> how much refrigerant there is).  In light of the 90 degree ambient temp,
> this seems low compared to the discussions I have seen on this site, however
> it shows that its "dangerously high" according to these gauges.  Any ideas
> why the rest of the world thinks the PSI should be lower?
>
John, anytime the high speed radiator fan kicks in (although the 84 may
not have that), it shuts the A/C compressor off.  The gauges that come
with the refrigerant cans go on the LOW side only.  If the low side is
that high, you could have a couple of problems; expansion valve stuck
open, bad compressor valves, over-charge with refrigerant, blocked
evaporator (too low of airflow), or possibly a plugged receiver/drier
and/or condenser.  You must remember to NEVER hook a refrigerant can up
to the high side of the compressor - it can blow up in your hand.  You
need a real set of gauges to monitor both high and low side pressures to
be able to troubleshoot effectively.  Just knowing the low side is 65-70
doesn't tell the whole story.  If the high side is 375 psi, then you're
overcharged, or you have insufficient airflow through the condenser, and
you get hot gas being delivered to the evaporator (instead of hot
liquid) which will open the expansion valve and the low side pressures
will skyrocket.  If you have 65-70 both high and low, with the
compressor clutch engaged and spinning, you're looking at a valve body
problem in the compressor (so, it could be lots of things).  Borrow a
set of gauges from someone and hook up both high and low sides (high
side is the line going from the compressor forward to the condenser -
the low side comes down out of the overhead from the evaporator), and
monitor pressures.  Use a garden hose and run water over the condenser
and record the effect on the pressures.  Post the results and we might
be able to help you find the problem.

Keith Hughes
'86 Westy Tiico (Marvin)