2003 Suburban HVAC Relay Heating Up

[Fitz98]

I have been trying to trace down intermittent HVAC issue in my 2003 Suburban 1500 5.3.
AC works mostly while in motion, but if I sit at idle too long the compressor stops kicking in.
My most recent diagnostics shows me that the relay is heating up and stops working. With my last troubleshooting experience when the AC stopped working while at idle, I checked the relay. It was very warm to touch. I swapped it with the horn relay and it started working again.
Can this just be a symptom of an old worn relay, or could there be something else causing the relay to heat up (Like a worn clutch or coil?)
The horn relay I swapped it with was starting to warm up to touch, but I did not wait for it to go into thermal protection. I imagine all these relays are as old as the vehicle is.
I also imagine that while in motion, the engine compartment stays cool enough to keep the relay from heating up to a point of failure, which is probably why my problem occurs mostly at idle.
Any advice?
Any such thing as a more thermally resistant high temp relay?

 

[eljefino]

I'd get an ammeter in there and compare it to what the clutch is supposed to draw.

 

[repairman54]

20 yr old relay will have carbon build up on the contacts causing resistance and heat buildup. Relays do wear out. Cheap to replace.
I would put a fresh one in and go from there.

 

[Dave9]

Agree, get a new relay. If something is causing excessive current, the relay should still be rated for as much as the fuse for that circuit so it should blow the fuse first, assuming it is the lone thing on that fused circuit, but you could measure the current if you want. I'd wait until after replacing the relay as they are inexpensive for major aftermarket brands bought online.

I imagine all these relays are as old as the vehicle is... Any such thing as a more thermally resistant high temp relay?

So the original probably lasted 20 years. 20 more years is not enough service life? In an extreme environment, I suppose there could be benefit to insulate the relay box from the engine heat, but doubt Florida is extreme enough to matter.

Another possibility might (or might not, just a theory) be that it is actually kicking the compressor on for a moment, but it pulls idle RPM down too low so it disengages it. Have you observed this happening in park to be sure there is no attempt to engage the clutch momentarily? That might also show blips of momentary RPM drop on a tach.

 

[dumkid]

I've seen old suburbans with bad fan clutches give the same symptoms. There's not enough airflow at idle to cool the condenser (although the engine doesn't overheat, i guess it has a big enough radiator)

If you have a mechanical fan, check the fan clutch