02 EVC AC question

[hcr]

Greetings

We are on extended trip and started having issue with AC.
System works fine initially, but over long drives there comes a time when it starts blowing significantly less cool air.
If we turn it off, then in 15-20 back on it works fine.

Last summer condenser, resistor packs and fans were replaced.

I suspect fans stop working but have yet to verify.

If true, what controls fans?
Other possibilities?

Charles

[kourt]

To me this sounds like one of two things: failing blower fan, or your evaporator is freezing up.

Your description of the process:

1. blowing cold air initially
2. blowing less cold air, but still blowing
3. turning off the system for a while
4. turning on again and enjoying cold air initially again

...sound like a classic freezing evaporator cycle, wherein you are thawing it out when the system no longer blows cold and you turn it off.

The blower fan is attached to the blender box on the passenger side of the van and can be exchanged pretty easily with some knee bolster disassembly.

The evaporator that might be freezing is the heat exchanger inside the cabin, on the passenger side of the blender box.

The frozen/not frozen condition of the evaporator is monitored by the E33 Evaporator Temperature Switch (VW part number 357 820 295 B, here's one on eBay that I bought recently) as seen in the Erwin diagram below. I think the diagram below is for the pre 1998 vans, but they all used the same evaporator temp switch located in the same place. Both Climatronic and manual air conditioning systems use this switch.

If this mechanical switch is disconnected or fails, the AC compressor will run 100% duty cycle and freeze up the evaporator. Note: the SD7V16 compressor in the 2001-2003 Eurovan is a variable displacement compressor, that runs continuously and varies the displacement from 8.1cc to 161.3cc via an internal pressure valve. [source]

Evaporator freezing will cause a loss of cooling. Normal function of the switch will interrupt the compressor function if the switch probe detects temperatures of 30F or colder in the evaporator probe tube.

The switch is designed with a probe that inserts 13" into the evaporator. It will be extremely hard to see, but with a cell phone camera you may be able to see into the probe hole in the evaporator and discern the plastic tube that accepts the probe and keeps it in the center of the evaporator.

You can remove the switch by disconnecting its electrical leads, unscrewing it form the evaporator housing base, and pulling the probe out of the evaporator, and test it by sticking the probe in a freezer and put a multitester on it set for continuity. The continuity state will change from complete to incomplete as the probe detects anything below freezing. Give it time. It will audibly click when the probe is in a freezing state and open the circuit.

This switch is just another in the series of switches (temp and pressure) in the AC system that can open the circuit for the compressor.

What I would do in your case is test the evaporator temperature switch first.

If you don't want to spend money on that part, you could use a DC Inkbird switch to do the same thing the mechanical switch does, and even have it programmable to whatever temp you like.

kourt

[TheOneTrueQuux]

[hcr]

Kourt

Fantastic guide - thanks.

We will be headed back to Tx aka HEAT after a visit with family in Ca.
Would we be ok on drive home turning system on/off as I described or does this risk $$ damage?

Charles

[kourt]

If you are on top of managing it, I don't see too much harm in the on/off method.

I agree with Quux--underfilled refrigerant conditions can produce these results as well.

Some say that not using recirc in the HVAC puts warmer air over the evaporator and reduces the chance of freezing. You might try that.

kourt

[dsh1705]

kourt - fantastic bit of information. This is why I love the Samba.
_________________
David
1705.net
95 EVC
ACU,098

[hcr]

Kourt

Thanks again- great info.
I’ll have refrigerant level checked prior to return trip.

Charles