Rabbit Air Conditioning Basics

I've started some preliminary troubleshooting of the air conditioning on my '84 Rabbit. Unfortunately, my Bentley doesn't really say anything about air conditioning. It appears that the refrigerant in my bunny is still the old R12, so I'm figuring that I will need to get it converted to R134a in order to get it charged. Here are my initial questions:

  1. From what I understand, turning on the A/C should have the effect of turning on the radiator fan. But what I don't understand is: the radiator fan only blows air on to the condensor. Where is the fan/blower that controls how much heat or A/C blows into the interior? I have a vertical lever for controlling fan speed on my dash, but it isn't working. It doesn't matter what setting that switch is on, the volume of air blowing out of the vents doesn't change. I'm not sure where to investigate this problem.

  1. As stated above, my blower (whereever it is located) doesn't seem to work with heat or A/C. But regardless, does the A/C function independently of this blower? When I slide the horizontal lever to A/C, what little air I feel coming out of the vents is not cold at all. I'm not sure if the temperature of the air coming out is related to issue #1 or not.

Thanks, Bryan Walton

Reply to
Bryan K. Walton
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Reply to
none2u

Hi none2u, Thanks for the reply. Unfortunately, I don't know the history of this air conditioner, as I've only owned the rabbit for about 7 months. I'd like to get it working, but it definitely isn't the most important thing on my list of repairs for this car. Regarding your question about the compressor turning on when I turn on the A/C, I checked that out this morning, after my drive to work. What I immediately noticed was that when I turned on the A/C, even on Max, the radiator fan didn't even start spinning. So, I think more important than the A/C is making sure that my engine cooling system is working 100%. So, first things first, I want to ensure that the radiator fan works. In the 7 months I've owned the car, I've only heard that fan come on one time, and it was several months ago, before summer. So, onto that. One question about that, the John Muir manual describes an A/C switch under the hood that controls the interaction between turning the A/C on and spinning up the radiator fan. But the book says that switch is located between the coolant expansion tank and the battery. However, on my '84, that space is taken up by the windshield wiper fluid tank. Does anybody know where this switch might be on an '84?

Thanks! Bryan

Reply to
Bryan K. Walton

Reply to
none2u

Hi again none2u, Slow progress, I crawled under my car during my lunch break and jumpered the plug coming from the radiator fan motor. Success! So I know the fan and the fan motor works. So, either my car isn't getting hot enough (which I suppose is great), or my tempswitch is toast. Theoretically, if the car was never getting too hot, because the thermostat was staying open, then in theory the fan would be running all of the time, correct? So, given that the fan is hardly ever running, am I correct in assuming that the thermostat is probably OK and I should zero in on the temp switch on the radiator?

I'm inclined to change that switch anyway. When I removed the plug from the switch, I saw that my switch only had two pins on it. From this page:

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seems my switch should have three pins. Perhaps this is also part of myA/C problem?

Thanks, Bryan

Reply to
Bryan K. Walton

Good.

No. There are two different items that keep your engine the right temperature: the thermostat and the fan. The thermostat keeps the coolant from circulating through the rad when the temperature is too low. Once it opens up, the coolant flows. On older cars with the side expansion tank, you used to be able to eyeball this by leaving the rad cap off and watching the flow. This doesn't work well on the cars with the external expansion tank.

Once the coolant is circulating, you also have the fan there to cool the coolant while it's running through the radiator, in case normal convection or airflow from driving isn't enough (like when stopped). The fan goes on and off depending on the thermo switch.

You can test the thermo switch by checking whether it is open or closed at various temperatures: you basically drop it in boiling water, and see if it switches on. The shop manual should have the right setting for your car. _Get the right switch_. Some of them are thread-interchangable, but have different settings. The correct operation of your cooling system (and your fuel economy) depends on this.

If your thermostat is bad, you get overheating, even though you're not pumping through the rad. Is your temperature regularly getting way high? (I had an engine with a marginal thermostat -- or maybe it was a water pump, I forget now -- that ran very hot but still was ok. The oil temp sensor was still well below where I was worried. But when the component finally failed and I had to replace it, the temperature went way down. I'd bought it like that, of course.)

Possibly. IIRC, the A/C cars (I only ever had one) had an extra pin on that switch that allowed the compressor to tell the fan to turn on. I believe there were two hots in the plug, and one ground. I will tell you that performance was so bad with the A/C on that I never ran it. (I hated that A/C anyway -- it was basically an add-on, and it showed. Doing any work on the car was a major PITA, and the Bentley had practically no information on it. This was on a 79, though; I assume later cars were better. Also, it was before the Net was so widespread, so there were fewer gearheads online.)

A
Reply to
Andrew Sullivan

Hi Andrew, I think this will be my next step. One question about your fuel economy comment. I see different switches for sale that allow the fan to come on at different temperatures. I'm assuming that for optimum fuel economy, it is generally better to use the standard, or "warmer" switch -- as opposed to one that would keep the car cooler?

One other question, I assume that if I unscrew that thermoswitch, that coolant is going to come poorting out, right? Do this mean that I need to plan on draining the radiator before testing the switch?

No. 95% of the time, I would say the needle on the dash is around 60% of max.

I'm not interested in throwing a lot of money at the A/C, but if I can make it work with nothing more than a recharge and perhaps a new thermoswitch, I'll probably do that. I wouldn't run the A/C much at all. But it would be nice to have on the rare occasion that I needed it.

Thanks! Bryan

Reply to
Bryan K. Walton

No. The right one is the one specified for your car. The combination of A/C vs no A/C, additional cooling components (like the oil cooler), different expansion tank arrangements, &c. are the relevant variables. It is possible that you'd want the fan to come on at a slightly lower temp if you spent (for example) a lot of time idling in the desert.

I now remember having had a car that had the three prong plug, but only a two-conductor switch; it did not have A/C. The shape of the plug is not a sure guide. So read the shop manual to tell you exactly what you should have.

Well, maybe not. What I used to do when I suspected the switch was just run the car idle for 20 mins or so. If the fan comes on, you know the switch works that far. If the car overheats, well, you know something else ;-)

A
Reply to
Andrew Sullivan

OK, moving along nicely. My thermoswitch works well. I idled the car after my trip home from work until the needle started getting up toward the high end. Around 85% of max, the fan came right on and cooled the engine right back down to around 60% of max. Now that I'm paying closer attention to this, I'm noticing that under normal conditions (my usual commute) the engine isn't ever getting hot. Furthermore, the fan seems to cut on only very rarely -- as needed. So, I think I can infer that my thermostat is also good (the car has not overheated even once, in the 7 months I've owned it). I have no reason to suspect it anyway.

So, given that I believe the cooling system is in order, I'm back to my original observation this morning, that the fan doesn't cut on when I turn on the A/C. I'm going to research this two-pin vs. three-pin thermoswitch issue further. Even though my switch works, as it pertains to coolant temperature, I'm not sure it is the correct switch for a bunny with A/C. If needed, I'll swap in a three-pin to see if that restores the connection between the A/C and the radiator fan. Once I have that working, I'll proceed with charging the A/C to identify what is or isn't working in that regard.

Thanks for your help, Bryan

Reply to
Bryan K. Walton

Is it possible that the switch on the interior controls is flaky? When you select AC, power should be sent to the compressor clutch and to a radiator fan relay, then to the fan. There is a sensor on the refridgerant line, turn on the AC and see if you get 12V from one of the wires on it. If that AC switch were bad, then the fan and compressor would not turn on when you hit AC. I have a 82 with AC and the radiator fan turns on when I hit the AC even when the compressor stays off because of no refridgerant.

Also, Im fairly sure that the AC switch is in parallel with the radiator fan thermo switch. That thermo switch should make no difference with the function of the fan with the AC. My thermoswitch only has two prongs.

Do you know if your AC system is discharged?

Bryan K. Walt> > On Wed, 07 Jun 2006 20:09:25 -0000, in rec.autos.makers.vw.watercooled > >

Reply to
thateb

Reply to
none2u

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thateb

Reply to
Erik Dillenkofer

Good question. That will be one of the things I'll check out next. Thanks for the suggestion.

Thanks for the clearing that up. I won't bother swapping out my thermoswitch then.

No, but I'm going to assume that it needs a charge. Plan to purchase one of those r12 to r134a conversion kits and move ahead.

Thanks, Bryan

Reply to
Bryan K. Walton

That definitely helps clear things up.

I think this is going to be my next step. I'm going to buy one of those r12 to r134a conversion kits and see what happens. If that makes no difference, then I'll probably make sure that the A/C controls are sending power to the compressor and move on from there.

Nice suggestion. Thanks.

Reply to
Bryan K. Walton

controlled by the A/C switch, when the A/C is turned on,

diode that keeps the A/C from turning on when the

the A/C compressor would turn on when the thermoswitch

low on freon, if the compressor won't kick in, then

Time to charge up the system and see what happens. Thanks, Bryan

Reply to
Bryan K. Walton

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