SOLVED !! - Thoughts on temp spikes with AC on
 

So I’ve done a bunch of research here and yet maybe I’m missing something?
My AC runs good as expected. Blows cold. However in NON-highway driving and especially at traffic lights the engine temp will begin a quick rise with the AC on.
The electric fans spin good and blow towards the engine. The fan clutch is good. The compressor sounds okay.
Normally the temp runs a little below the midpoint on the gauge and will increase a bit above it if I’m sitting at idle for 15 min plus but nowhere close to redlining. All components of the cooling system, and I mean ALL, have been replaced over the last year or so.
I’m outta guesses. Any ideas?

Im kinda getting to a point where if I can’t figure it out I’m still looking at yanking the system and losing some weight. It’s an 80 buck commitment for a d2 pulley and a new belt. I’d rather have air but if it remains undiagnosed then I’m ready to scrap it.

what type of radiator are you running? What type of fan clutch?

I replaced my fan clutch with an Astro van clutch.
Noticed that even with good elec. fans at idle sitting in drive thrus and such would creep up to 212 in summer. Found that if I raise the rpm up to 1200-1500 it would stay at 186. All numbers are from an UG.

Clutch is original stock LR. Radiator is an all makes am replacement.

Forgot to mention I had a credit to use up so I applied it to a good deal on a pair of 10” flex a lite fans. After really feeling my current fans out they just seemed like they had no balls. Worst case I got a pair of decent electric fans to play with.
Considering getting my old stock radiator repaired. It’s sitting out in the shed. Ugh....

I can concur with this. My thinking was that either the engine fan would move faster as a result or the water pump was turning quicker thus moving more coolant at a higher rate, or both? If I don’t run my ac it’ll still increase temp at idle but very very very slowly. With ac on it’s pretty damn quick.

If nor already done you may want to remove belt and check the a/c clutch pulley bearing for dragging. A failing bearing can put quite a load on an idling engine.
......

interesting thought about the A/C bearing.

I had the same as ROB99 this past summer. I re-cored the radiator after replacing the fan clutch the summer prior. It hasn't been hot enough to really test it out however.

ROB, if you are running the original fan clutch, replace it. The difference between my 16 year old clutch and a new one (OEM bought from AB) was pretty significant. The new is MUCH more aggressive.

Having said that, a new fan clutch did not solve my problem.

Check the alternator too for bad bearings while your at it - mine where toast and it was a noticeable diff (like I added 5hp to the engine) once I replaced that.

I have a 4 core all aluminum rad - brand new hoses, pump, tstat - etc. Mine will still creep up to 220 with the a/c full blast on a hot day at rush hour

You may be on to something here. Checked it tonight and there’s that familiar jing jing rubbing noise when I spin the pulley. Looks like I’m putting a bearing in shortly. Even if it doesn’t solve the problem it may lengthen the life of the compressor....