1990 240 wagon ac project

[93Regina]

the sight glass was showing a lot of bubbles. So, refrigerant low..

Maybe, maybe not...On a HOT DAY, then evaluate.

Is your hot water valve by-passing? When engine is upto temp, then turn on heater fan to high, with temp control set to cold. Is it warm inside?

[edelmatt]

I live near Fresno, so every day from here on out until October will be hot. It was 92 today. With the fan turned to high, and the temp set to cold (which is how I had it set as I drove around for 20 minutes) it was just basically pushing around the ambient temperature.

Does the hot water valve send hot water through the same core as the coolant? Sorry I'm learning as I go here.

[BBslider001]

I'll be watching this as our 1989 740 has no AC as well. It seems they are the same systems? Sorry, not trying to hijack. Thanks! I hope this works out on the cheaper side for you!

[edelmatt]

Thanks! I hope this works out on the cheaper side for you!

Me too, thanks! Good luck with the 740.

Open question, if anybody has an answer: if I see action in the sight glass, can I assume that the system is circulating? Or do I still have to be concerned about a blockage on the low side?

[abscate]

I would be much less worried about blockage and looking for leaks. ACs like to be run every few months to keep the lubricant distributed, which is one of the reasons bring a dormant one back to life can cost 1000 bucks.

[93Regina]

if I see action in the sight glass

Two People - One starts vehicle and engages AC while the other looks at sight glass, and listens for AC clutch to engage (click); if bubbles seen, then there is some refrigerant in system.

[93Regina]

Does the hot water valve send hot water through the same core as the coolant?

AC system is separate from water heat system.

But, if water system's temp-control-valve is by-passing, there will be heat inside cabin.

Inside cabin, where fan blower is located, there are two heat exchangers, one for AC (called evaporator), and one for heater, called heater core.

[edelmatt]

There is refrigerant in the system. Verified. Pressures unknown. Waiting to run into my AC neighbor to see if he can help get a reading and possibly recharge for me. The only piece I can really look at right now is why the switch/knob only seems to engage the compressor clutch sometimes. I don't know the functionality of that control. But I surmise that it is both a sensor and a switch. If I can simulate "on" by just shorting two of the leads then that would make the rest of the process easier. If I can't keep the compressor running it'll be tough to finish the job.

93regina you've been pretty helpful so far. What do you know about that switch?

Edit: Took a picture of the switch and the schematic in the Bentley manual:

switch: https://docs.google.com/file/d/0B-msuWGrrOrbb0NfWU8xWkJDR3ZxZlhkSlhhNElqeGQzclVJ
schematic: https://docs.google.com/file/d/0B-msuWGrrOrbdV96YWowemxSb3dBNWpUX25wc2V6cGxmV25B

I think the two green wires are for the thermostat switch, and the knob varies the response of the thermostat. When the thermostat warms past the threshold set by the knob, it will short the two greens together and send power to the switch on the receiver/drier. Only then will the compressor turn on. I'll wait and see if anyone disagrees, but my thought would be to wire in a rocker switch to the green wires and take the switch/thermostat out of the mix.

[93Regina]

If I can simulate "on" by just shorting two of the leads

Where sight glass is located, is there an electrical plug there? When engine is not running, jumper a wire from battery to one of those two female terminals on that plug...when you hear compressor click, then you know what to do. Do not run a compressor full-time that way

That is a thermostatic switch, and they do fail...normally they are placed on evaporator...there are generic replacements, maybe on ebay...look for part number, name, etc.

[edelmatt]

I bypassed the on/off/thermostat switch/knob by putting a toggle across the green/green wires (on/off), and shorting the two leads that go to the thermostatic switch. Now I can force the system to run anytime. Hopefully next week I'll have time to take it to a shop for a leak down test. That will tell me whether I should recharge with R12 or move towards an R134 conversion.