My 1992 F-150, 5.0, had to have a new A/C installed, when truck was "idling" and A/C came on it would stall the engine. The mechanic brought in the A/C distributor agent to help find the problem. No find on 1st unit. A second unit was installed and still could not find the cause why it was stalling the engine when A/C engaged. The electrical plug in to the unit receptacle had been previously damaged and a separate wire was installed in its place to the opposite end juncture of the connection. The mechanic was very positive this wire replacement was done correctly. To stop stalling the engine the RPM was increased from 500 to 750 which solved the engine stalling. I am still not happy with this situation. I bought the truck at 5 years old and the apparent original A/C never stall the engine and when it died it went out in smoke and froze and burnt up the serpentine belt.

Anyone experienced this? Any suggestions or solutions?

David S

 

What engine does the truck have? 500 sounds like rather a low idle RPM. Most Diesels idle higher then that. My truck idles at about 800. Have you tried revving the engine up, turning on the A/C, and then idling back down slowly to see at exactly what RPM it stalls out at?

 

Thanks Rusty, it is not a diesel, its gas 5.0, 302/304 cu.in. and EFI. I don't have a rpm gauge on the truck. My mechanic uses one of those expensive computer boxes to set rpm etc...
The 750 rpm is high enough to keep the engine from stalling. Supposedly the engine is idling at 500 rpm and when a/c comes on the rpm drops but engine does not stall and immediately and noticeably increases to the higher rpm. When a/c is turned off engine returns to the slower rpm.
Also the vehicle speed has to be higher than normal for the auto/mat transmission to shift gears when the a/c is engaged.
Both you and in2trux came on my email but I don't see his post here?

David S