AC question

[fiatslug87]

What does it mean if the air conditioner blows cold then warm then cold again, and cycle repeats. Is it a sign of low charge, compressor problem, etc.? Thanks.

[jdog]

Could be a few things,  is it r12 or 134?  low charge most likely as the compressor is kicking on and off.

It could also be a pressure switch or a relay failing.

[scaleless]

It's possible it could be a few things, but most likely it would be a clogged expansion valve.  If debris clogs the valve, the refrigerant entering the evaporator is too hot and would not blow cold.  On vehicles of this vintage, seized or clogged expansion valves are common.  On Renix, it could also be a sign of a faulty thermal sensor. The one on the outside of the heater box with the long capillary tube.  It switches the compressor clutch on and off depending on the temperature of the evaporator.  It could also simply be a failing compressor clutch. 

 

To troubleshoot, I would look to see if the compressor clutch is engaged or disengaged when it starts running hot.  If it is engaged, then it's likely the expansion valve.  If it is disengaged, then I would bypass the thermal switch with a jumper.  The compressor clutch would then engage unless the clutch was faulty.

 

Edit: for some reason I completely forgot about the low pressure switch until jdog mentioned it haha.  Test that the same way you would test the thermal sensor

[Minuit]

How much has the system on this truck been messed with? It is one of your trucks, right? Has it been converted? I'm assuming here that it's at least been converted.

 

Put manifold gauges on it before assuming anything is broken. Post those readings as well as the ambient temperature when you took the reading. Check to see if the clutch stays active {rev the engine to simulate driving), and if not, post the gauge reading when it kicks off.

 

You aren't one of those people who need a warning to not shove more refrigerant into it before you get more info, but, yeah, don't do that. That is a very common way to make the problem worse.
 

[cruiser54]

This^^

[fiatslug87]

Thanks guys, I'll borrow the gauges from my neighbor when he's around.

 

I was hoping for the "I had these same symptoms and it was this" answer. Just being lazy.