Automotive Air Conditioning Information Forum (Archives)

Scratch on Wed May 16, 2012 3:44 PM

Year: 1979
Make: Ford
Model: Granada
Engine Size: 250
Refrigerant Type: R12
Ambient Temp: 68
Pressure Low: 34
Pressure High: 140
Country of Origin: United States

I created another message only so I can enter the low side and high side pressure readings. I took these readings in the garage and with the engine idling at 900 rpm. The A/C always blew 42 degrees cold until the compressor input shaft seal failed. I installed a new rebuilt compressor and new filter/ drier. System was vacuum tested and mineral oil added. R12 was charged in yesterday in the garage and A/C blew 45 degrees. The expansion valve and connecting tube were coated with frost. I drove the car several miles this morning and the coldest I saw was 50 degrees. I got home and immediately took the above readings. I got 45 degrees again in the garage when I revved the engine. I'm guessing that with the car stationary and less airflow on the condenser I'm getting colder A/C. I have the following questions: 1. Do these readings seem normal? 2. Should I add more refrigerant? 3. Do the readings indicate a bad compressor? 4. Will a new expansion valve help? I'm not happy with 50 degrees cooling and would like to get back to at least 42 degrees if not cooler. Any input would be appreciated.

Scott

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scott johnson

mk378 on Wed May 16, 2012 5:07 PM

Is this a pressure regulated system (POA or VIR)? In that case try shutting off the interior blower, see if low side drops. If it is always 34, your regulator valve isn't working right.

Also, getting a lot of frost right after the TXV but the evaporator outlet and the air is not very cold does suggest insufficient charge. The system may be fitted with a sight glass, but you can't trust those in cool weather.

Edited: Wed May 16, 2012 at 5:20 PM by mk378

Scratch on Wed May 16, 2012 9:53 PM

mk378,

This Ford Granada has a BPO (bypass orifice combination valve) consisting of an expansion valve and a STV (suction throttling valve). According to my Ford Factory Manual, ".... evaporator outlet temperature and evaporator pressure are sensed internally, eliminating the need for the capillary and bulb."

As far as I can tell, my A/C system consists of this BPO assembly mounted on the firewall, evaporator, condenser, compressor, filter/drier, and hoses connecting the components together. I have uploaded a picture of the BPO. Here is the url: http://www.autoacforum.com/forumimages/DSC00406.JPG


I left the gauges connected and with the engine off, the low side reads 68 psi and the high side reads 75 psi. I believe these readings are correct because when the compressor is operating the low side goes to 34 and the high side goes to 150. I'm wondering if it was too cold in the garage to recharge the system. I'm going to wait for warmer weather and try recharging in the hot sun.


Scott

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scott johnson

Edited: Wed May 16, 2012 at 10:02 PM by Scratch