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Cannot get a high side reading on Old's Ciera (GM A-body)

Cressida on Sat June 18, 2011 8:49 PM User is offline

Year: 1993
Make: Old's
Model: Ciera
Engine Size: 3300
Refrigerant Type: R-12
Ambient Temp: 95
Pressure Low: 30

I have a 1993 Old's Ciera (same as Buick Century - GM A-body) with 3.3L engine and R-12.

The high side attachment port for my gauges does not give me any pressure reading at all. After I remove the screw on cap from the fitting and look into it I cannot see any shrader valve that you normally would see. The car has a charge but I wanted to just check out the high and low pressure to make sure they are within reason. I do have and used the adapter fitting that you have to have to hook up your gauges to the high side for those systems like this that use a different high side size. (guess it is 3/16 to 1/4)

I don't get it why would GM have a high side fitting with no means of being able to use it with a standard gauge set? What do I need to do to be able to get a high side reading on this car?

Also, I cannot seem to find the A/C evaporator drain at the firewall to see if it is clear and draining OK. I am looking down from the top side of the engine compartment. Can someone tell me where I should look on the "black evaporator box" attached to the firewall to find the drain? Or, is it only accessible from under the car?

mk378 on Sat June 18, 2011 9:43 PM User is offline

You need the GM specific 3/16 adapter. It's called a "deep throat" valve. They were only used at the very end of the R-12 era.

bromodragonfly on Sat June 18, 2011 10:18 PM User is offlineView users profile

The high side fitting has got to have a schrader or some kind of isolation valve, or refrigerant would just piss out of it once you removed the cap. It's probably not clogged or restricted because you see zero flow through it. It would be pretty bad for GM to design a high side discharge line and just use a flare cap to "seal" that access off.

The fittings I have for working on some GM or ford models have a female flare connection (I think it's 5/16") with a schrader depressor, which then has a copper tube that is brazed to a 1/4" male flare on the other end. If your adapter is just a female flare bushed to a 1/4" male flare, and does not have a schrader depressor, you will not see any pressure through that adapter. If you want, get a pocket screwdriver and GENTLY press it into the open flare (When the car is off and the AC pressure is static) to see if you get a little burst of pressure.

My guess is GM does that on purpose so that you need a specialized adapter that is probably only available at HVAC/auto wholesalers. Kind of forces you to bring the car into the dealership if you're having major AC problems and can't easily diagnose it.

At least you have a high side fitting. The only access fitting on my 87 Beretta is a 1/4" flare on the low side accumulator.

I don't know enough about your car to tell you where the drain pan is. I'd check out that black box to see if there's any drain piping or tubing on the bottom of it. It makes the most sense to have the drain directly underneath the evaporator, where the warm air blowing over it will condense moisture on the coil and it will drip off. Maybe since the evaporator isn't inside the dash, and the system isn't designed for freezing temperatures, they don't even have a drain?

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There is no knowledge that is not power

GM Tech on Sun June 19, 2011 8:33 AM User is offline

Deep throats were used on '93's GM at end of R-12 era as mentioned--they are on many vehicles---so you need the adapter----funny- I think it was me who gave it that nickname 20 years ago.........

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Cressida on Sun June 19, 2011 10:54 AM User is offline

Thanks for the help. I had never heard of this adapter and was pulling my hair out. Now I know what I need but this is ridiculous.

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