I have search the Forums, but cannot find anyone having my issue. The A/C blows ice cold every day on first start up and also when traveling at speed on highway. But once truck has warmed up and running at city traffic speeds, the blowing air goes pure hot! Not talking about just warm, I mean hot air like heater is on. I first installed a manual shut off valve in the heater hose, this had no effect. Had the A/C system purged, checked and recharged. Also had the A/C clutch gap checked.

Why does the A/C cooling return to normal every time I am back at highway speeds? Could the vacuum pump be failing after is gets hot? Does anyone know if the "blend door" has to see full vacuum to keep the heater core air flow shut off?

 

17 years of trucks, countless engine and transmission combinations.
No maintenance history
No real modification or change history
No indication of proper engine monitoring gauges
No location or environment indication, maybe somewhere in Oklahoma, however those tags are often not updated.

Details.....

 

Sounds like an airflow issue across the condenser.

 

Jimmy

2002 F350 Lariat, 7.3 Auto, DRW, Crew Cab, Long bed, 4:10 limit slip. 249,000 miles, owned for 14 years, BTS auto and tune, do my own maintenance