Their is a relay in the a/c system that is to cut off the system when
coolant reaches a certain temp.....Either that relay is bad, or the switch
that triggers it , is...............

Also, maybe you had too much pressure in the a/c system.............Mine
hits 200 on the high side, max, and it will freeze you out of the
car...........

Adam P
81  Westy "The Brick "
70 Single Cab "Whitey"
74 Beetle "Ol Yeller"
73 Transporter (STILL at paint shop)
1988 Vanagon Wolfsburg
75 Campmobile "for sale'
Used Vanagon Parts for sale (mostly aircooled)
----- Original Message -----
From: "TinkerMan" <tinkerman007@YAHOO.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Monday, August 12, 2002 9:07 AM
Subject: # Importance of pressure and temp monitoring (long)

> Hi Volks!
>
> Recently, I had the radiator fan speed reduction
> resistor go down on me. As a result, the radiator fan
> would turn on only at high speed when the coolant was
> really hot.
> I didn't pay attention in the beginning, thinking it
> was the hot weather...
> Well, in the end, this resulted in a blown A/C dryer
> pressure relief (requiring replacement of dryer and
> refrigerant, $$$$$) as well as a blown coolant hose.
>
> The A/C pressure relief blew because my A/C serviceman
> hacked a replacement pressure switch which somehow
> didn't protect the A/C system from high pressure.
> Why high pressure? because the radiator fan didn't
> cool the radiator most of the time, until coolant was
> really hot (the resistor burned in the common circuit
> that controls both the low speed as well as the A/C
> minimal speed activated when A/C is on). In the end,
> that was enough to cause exessively high pressures in
> the A/C to blow the pressure relief valve.
>
> And why did the collant hose blow? because the higher
> engine coolant temperature resulted in higher
> pressure. Of course the coolant pressure cap should
> have relieved it (and might have if it reached 15psi),
> but old hoses always are a weaker point in the
> system...
> Still have to check the coolant pressure release cap
> for 15psi, although it was lately testy OK. Darn,
> can't rely on those dealer mechanics (BTDT...).
>
> Also, there have been many posts regarding engine oil
> pressure monitoring. Many say that catastrophic
> failures can be avoided if unordinary pressures (both
> low and high) are noticed. Even the builtin so-called
> "dynamic pressure monitoring system" isn't enough and
> won't detect exessive pressure instances at all (e.g.
> when pressure relief valve is stuck).
>
> Which leads me to the obvious conclusion that all
> pressures of important systems must be monitored and
> warned against exessive pressures: Oil, coolant, A/C,
> etc.
> I know this sounds paranoid but from my experience
> noticing a simple failure promptly and taking action
> can save huge sum$ and grief resulting from
> catastrophic failures which could have been avoided.
>
> SSSOOO...here's what I'm looking for:
> 1. Good point to check coolant pressure. Methinks that
> a convenient spot would be the "T" where the left head
> connects via hose (VW 025-121-058M) to the coolant
> manifold. A "T" could be added for the sensor without
> changing the system. Any better spot, e.g. the coolant
> distributor, outputs to the rear heater which I don't
> have? I don't want to drill a hole in the coolant
> expansion tank like someone suggested...(I've had
> enough trouble with that one!...).
>
> 2. Good spot to measure oil pressure: Many have
> recommended the 0.3 bar pressure switch location with
> extension hose and dual sender or "T" with standard
> sender: Is this BEFORE or AFTER the oil filter?
> Anyway, I don't like this extra hose dangling around
> there (even tied to something) but maybe there's no
> better option. Any better ideas?
> And I want to connect to it THREE senders: the
> original 0.3bar, an analog sender and a high pressure
> alert (in case of overpressure). Anyone know what
> would be the maximal recommended oil pressure? What's
> the spec of the oil pressure relief  valve?
>
> 3. Good spot to measure A/C pressure: wouldn't be easy
> (no place to tap in). Maybe use the integral pressure
> switches with a buzzer, but have to make sure the
> sender is working OK first.
>
> ******
>
> After we finished with the pressure issue, now comes
> the temp issue...
>
> 1. Coolant temp is monitored in the dashbord, but is
> quite unreliable: I had a double failure where my
> coolant leaked overnight, and my coolant level sensor
> (in the expansion tank) was cracked and allowed
> coolant to seep up to the connector, so when I drove
> happily away my dashboard meter showed nothing (temp
> sender was measuring air temp in the thermostat...)
> and the coolant level sensor indicated all was well
> (because the wire connnector above was wet, fooling
> the coolant level "relay" to think there was enough
> coolant...:-(
> Well, since then, I've added a seperate sensor right
> on the #3 head (hottest?) near the coolant exit
> (there's a threaded standoff there) and it works
> great. I even have an alarm circuit that can be set to
> a certain threshold, both for coolant temp as well as
> head temp (near the coolant exit). I thought about
> even adding another sensor at the exhaust port
> (another threaded standoff there) but I'm not sure if
> my sensor will stand those high temps.
> Anyone have a wide range thermoprobe to measure what
> temps can be expected there?
> I'm just wondering where is the best place to sense a
> catastrophic failure (coolant or oil loss) resulting
> in overheating. This is more relevant in aircooled
> engines, but can be used to the benefit of W.C. too.
> Anyone know what's the best place to measure temp on
> A.C.? Maybe there's a similar location on WC since the
> engines are based on the AC design?
>
> 2. Measuring oil temp: I'm aware of the various
> methods of measuring this (drilling sump plate and
> installing sender, but prefer not to drill, or temp
> sender dipstick which is claimed not to be accurate).
> All in all, I think I've got it covered with my other
> temp sensors.
>
> 3. I need a source for LOW COST but reliable senders
> for the above. VDO might be good, but are defenitely
> not cheap. Also, ideas for tapping into the various
> systems to be monitored.
>
> 4. The most important issue: with all those sensors
> and senders, I need to display them all...
> I don't have room (or desire) for an airplane cockpit
> in the dash, so I'd like to have a single meter there
> switchable to the various senders. The problem is that
> usually each sender has it's own characteristics and
> matching gauge. I'll have to scale them down for a
> single compact meter, hoping they all are referencde
> to ground...
>
> Well, that's my rambling. If anyone has implemented
> such monitoring stuff, I'd be glad to hear practical
> experiences and recommendations...
>
>
> =====
> Cheers, T-man.
>
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