A/C Only blows cold when radiator fan comes on?? plz help

[blacks]

@Callmejc27
HI I THINK I HAVE THE SAME PROBLEM SO CAN YOU TELL ME WHAT THE DEALER SAID

[metalshark]

Originally Posted by blacks

@Callmejc27
HI I THINK I HAVE THE SAME PROBLEM SO CAN YOU TELL ME WHAT THE DEALER SAID

The ECU cannot directly turn on the fan. A relay must be used to source that much current. It is unlikely that the relay has an auxiliary set of contacts to notify the ECU when it has failed. On my Yaris the fan comes on every time I turn on the AC.

[CTScott]

Originally Posted by metalshark

The ECU cannot directly turn on the fan. A relay must be used to source that much current. It is unlikely that the relay has an auxiliary set of contacts to notify the ECU when it has failed. On my Yaris the fan comes on every time I turn on the AC.

The ECM controls the cooling fan via a relay (I did not say that it does not have a relay, just that the ECM has complete control over this process). Normally this does happen when the AC is turned on. The AC tells the ECM via CAN bus message that the AC compressor is running (the AC ECU fires the compressor directly, without a relay) and the ECM turns on the fan via the fan relay.

Since the OP's fan and compressor both turn off, my suspicion is that the AC ECU is logging a DTC and shutting down the AC.

[metalshark]

Originally Posted by CTScott

The ECM controls the cooling fan via a relay (I did not say that it does not have a relay, just that the ECM has complete control over this process). Normally this does happen when the AC is turned on. The AC tells the ECM via CAN bus message that the AC compressor is running (the AC ECU fires the compressor directly, without a relay) and the ECM turns on the fan via the fan relay.

Since the OP's fan and compressor both turn off, my suspicion is that the AC ECU is logging a DTC and shutting down the AC.

If the fan relay is an open loop control line then failure of the fan relay will cause high head pressure at the compressor. Pressures too high or to low will cause the ECM to shut down the compressor clutch for system self protection. Many times the fan relay coil will develop an internal short that causes a cyclical thermal related failure that is harder to diagnose because some times it works, and some times it doesn't just like an ignition coil pack.

[CTScott]

Originally Posted by metalshark

If the fan relay is an open loop control line then failure of the fan relay will cause high head pressure at the compressor. Pressures too high or to low will cause the ECM to shut down the compressor clutch for system self protection. Many times the fan relay coil will develop an internal short that causes a cyclical thermal related failure that is harder to diagnose because some times it works, and some times it doesn't just like an ignition coil pack.

If it were the fan relay, the car would likely be overheating, rather than just having an AC issue. In 20+ years as an Electrical Engineer, I don't think that I have ever seen an intermittently shorting relay coil. If it actually did so, it would pop the fuse.