I'm getting my truck ready for a summer vacation trip and the last time I had it out In February I noticed the AC duct temp was not as cold as other times. I checked the system with AC pressure gauges and had a digital thermometer for temp readings. Now with an outside air temp of 71°F The low side pressure reading was 35 PSI and a high side pressure of 225 PSI with a duct temp of 52°F at idle and 47°F at 1300 RPM.

The 134A pressure chart says that at 70°F low pressure should be 35-40 PSI with a high pressure reading of 145-160 PSI. Seeing that the trucks low pressure was correct, albeit on the low end of the specification, the high side pressure was 65 PSI to much indicating a slight blockage or a poor operating orifice metering valve. With the truck's AC system being 25 year old it was time for some maintenance to get it up to peak operating performance.

I replaced the high-pressure line from the condenser to the evaporator which comes with a new orifice tube in it. I also replaced the accumulator. I evacuated the system with a vacuum pump for 1 hour and then left it in a vacuum for a half hour to check for leaks with none found. The system was recharged with 2 pounds (32oz) of 134a and 2oz of PAG 46 oil for the replaced accumulator. The post repair test readings at idle were outside air temp 67°F, low side pressure 25 PSI, high side pressure 140, air duct temp 36°F.

So, for maximum summertime cooling test the truck's AC system and repair as needed.

Happing motoring,

Dan

Any update on this? I did the same thing to mine along with a new evaporator and was disappointed with the results. Im about to add cut off valves to the heater core and inslate the ac lines from the orfice to the cab and see if that helps.

1 hour ago, yohon said:

Im about to add cut off valves to the heater core and inslate the ac lines from the orfice to the cab and see if that helps.

No need to insulate lines. The AC system on these truck cool very adequately. Likely, there is something not right with your system.

If you install the heater core shutoff valves and the the AC works much better, then you probably have a blend door problem - either with door seal leakage or the blend door is not operating to its full travel limits, thus some of the circulating air is still being passed through the heater core.

I have a heater core shutoff valve that I use in the hottest part of the summer. The difference is really unnoticeable when the truck is parked inside and used for the first time on a hot day. However, after being parked in the sun for a couple of hours or more, there is a faster cool down because the heater core has not heat soaked the dash, and when engine is started, there is no hot coolant entering the heater core to conduct into the cabin. This is when there seems to be the best benefit to using a heater core shutoff valve.

• John

51 minutes ago, Tractorman said:

No need to insulate lines. The AC system on these truck cool very adequately.

I had the lines off and had the insulation in stock so why not wrap the lines, no harm no foul.

54 minutes ago, Tractorman said:

door seal leakage or the blend door is not operating to its full travel limits, thus some of the circulating air is still being passed through the heater core.

The heater valve shutoff valve is a good idea. What type of valve and where was it installed?

Edited 5 hours ago5 hr by IBMobile