[s-cars] A/C strength, 93 S4

[Ernest Seow]

Your AC switches are most likely doing this, but you need to have gauges on 
the vehicle, as this does not mean they're bad, just working they way they 
should. If the system is too high or low on charge, this will happen. If you 
have a blockage on the high side, the high switch will cut the compressor 
off (too high charge or blockage) when the system reaches too high of a 
pressure and also if the system is really low, the low side switch will do 
the same since the low side will drop too low when the compressor is on. 
When the system is off you should have equal pressure all over, but when the 
compresor kicks in, if either side goes out of range the system kill the 
compressor to prevent damaging the unit. I have seen the recirc not work 
sometimes, and I think it has to do with temp settings. I would try to solve 
your compressor problem first, because if the AC control head see's 
something wrong, it may affect your recirc operation at this time. One easy 
check is to feel the condensor or high line going from the condensor to the 
evap. If line get hot quickly when the compressor kicks in, you have a 
blockage. It should be mild hot to warm the closer you get to the evap when 
operating correctly, until you reach right at the line to the evap. This is 
where your orifice tube is, from that point on it should be cold. Any spot 
you find that quickly changes from hot to cold except at the orfice tube is 
a blockage. Now, on the low side, if you accumulator is freezing up, then 
its bad, (blockage or fully saturated). If you find that the evap line to 
the accumulator from the evap is ambient temp or cool, and find along this 
line a cold spot, then thats another sign of a blockage. Anyway, as to not 
run on too much, most AC problems are charge level, bad accumulator or 
blocked orifice tube (has filter screen). Check those first and see what you 
find. Since your AC comes on and shuts off usually means your compressor is 
putting out good pressure, but the system sees something is wrong.
Regards,
Ernest

>From: JR <audiurs4 at mailforce.net>
>To: Ernest Seow <ezveedub at hotmail.com>
>CC: s-car-list at audifans.com
>Subject: Re: [s-cars] A/C strength, 93 S4
>Date: Wed, 26 Jul 2006 11:06:40 -0500
>
>What does it mean when the compressor seems to cycle on and off  every few 
>seconds or so?  Also, when I press recirc, it just shuts recirc right back 
>off immediately.  It will not stay on recirc.
>
>JR
>
>
>
>Ernest Seow wrote:
>>The key to good AC is make sure you have sufficient high side pressure 
>>when you know the system is fully charged. If the low side is too low and 
>>the highside is too high with the correct charge, then replace the orifice 
>>tube if you haven't already done so. Its the cheapest part. They tend to 
>>clog as the car get older from normal debris wear from the compressors. 
>>Also replacing the accumulator will help also. An old accumulator that is 
>>saturated will tend to drop efficiency. Over time, moisture still gets 
>>into the system from the rubber hoses, thats why most AC shop replace 
>>them. Also make sure your system is running on recirc, and not fresh air, 
>>so check the flap to make sure it operating. When ambient temps rise above 
>>80+ deg, the cooling temp will rise also. There is a chart to check this 
>>with Audi/VW vehicles. The design drawback of the UrS4/S6 AC is that the 
>>AC system is placed outside in the plenum, not inside under the dash like 
>>newer vehicles, so also makes the AC not as cool. I might attempt 
>>insulating my AC casings as its very hot and humid here in Florida.
>>Rgeards,
>>Ernest
>>
>>
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