Another AC Question

[Guest Steve Rawlinson]

I've been reading as many AC posts as possible and am still confused.

1. I've cleared all codes

2. Low side pressure reads 120 PSI when engine is off

3. Low side pressure reads 55 PSI when engine is running

Outside Temp. is 85 +

Running AC at 60 -- High Blower

Air is "Cool" - After 1/2 hour starts to get colder but will shut down if left on for any length of time

Don't know how to check High Side

Do I add more R12 and to what pressure ??

Any help would be appreciated

[harry yarnell]

55# is way too high. I'm assuming you're using R-12; low side running should be around 32#. If you're using R-134, look for 40#

[Guest Steve Rawlinson]

55# is way too high. I'm assuming you're using R-12; low side running should be around 32#. If you're using R-134, look for 40#

Thanks Harry

What can I expect ??

Will the AC get colder faster ?

Will this stop the system from shutting down and eliminate the 447 code from coming on

Is it important to have the High Side at a certain pressure

Steve

[harry yarnell]

Bleeding off some Freon will bring the pressures down, and ,theoretically give you colder and quicker chilled air. my concern is this 'shutting down' you speak of. A code 447 indicates low Freon, but you stated you've got 55# with the engine running. You may have two issues here; a bad sensor, and an overcharge. Are the radiator fans running ? If not, pressures will be VERY high and poor to no cooling. Check the fans before you bleed Freon. As for the high side, 330# on a 90 deg. day is about right. Both high and low pressures vary directly with ambient.

Edited July 19, 2013 by harry yarnell
add additional sentence. (see edit history)

[drtidmore]

Steve, per the GM 1989 Reatta/Riveria service manual, Code 447 sets, and I quote, "Code B447 will set if the low side temperature drops much too quickly during compressor engagement or the low refrigerant pressure switch opens during compressor engagement". Since you have indicated that your unit takes time to begin producing cold air, we can pretty much rule out the low side temperature dropping as the cause of code B447. As Harry pointed out, 55# suction side at 85 degrees is too high and certainly would contraindicate actual low refrigerant as 55# would indicate too much refrigerant which reduces the cooling capability of the unit.

The code 447 is likely either a failing low pressure switch, a bad connection to the switch, or bad wiring between the switch and the BCM.

Since the code B447 sets well after a period of operation, this may be a COLD associated situation since the low pressure switch gets VERY cold during operation as it sets immediately after the metering orifice which is the COLDEST point in the system just at the entry to the evaporator.

The low pressure switch, as well as the high pressure switch are located under the removable plastic cover just below the windshield under the hood at the left side of the area. The leftmost pressure switch (looking from the front of the Reatta) is the low pressure switch. Between it and the high pressure switch about 6 inches to the right is a tube housing the refrigerant orifice tube which meters the high pressure refrigerant into the evaporator at a much lower pressure.

You can remove the connector from the low pressure switch and SHORT the connections in the connector. Since your system does engage the compressor initially, we know that the BCM is supply the 12V power to the low pressure switch, so no need to go down that trouble shooting tree.

If shorting the terminal in the low pressure switch results in the AC running properly (ie it does NOT shut down or set any codes), then I would first try shooting some contact cleaner into the low pressure switch as well as the connector and mating and unmating several times to ensure that what you are experiencing is not a temp related intermittent connection (the low pressure switch get VERY COLD).

If the conditions continues after cleaning the contacts, then replace the low pressure switch and REGARDLESS, you need to remove some of the R12 (legally it MUST be captured and reclaimed). The suction (low) pressure side should be in the mid to upper 30s under idle conditions.

FYI, I just did a complete retrofit of compressor (had failed), accumulator and orifice along with moving to R134a, so all of this very fresh to me.

David Tidmore