My 91 Cherokee has been overheating since I converted my AC to r-134a. I've replaced the thermostat with a lower temp thermostat and did a tranny flush and still red lines with the air on. When I turn the air off it drops to about 210 fairly quickly. My therm housing cracked and I replaced it with another from a junk yard. I'm having a baby soon and need my AC at all times. Help please

 

Is your auxiliary fan coming on with the a/c?

 

Yea it turns on after it gets a bit warm

 

Its suppose to come on when you switch the a/c on.

 

I'll see what the deal is when I get off today and let you know the progress

 

almost guarantee that the fan isnt turning on with the ac. what is supposed to happen is this:

a/c turns on
aux fan turns on to cool the condenser (the condenser gets hot so the freon gets cold)

if the fan doesnt come on with the compressor, then the condenser still gets hot, and then the coolant gets hotter because the radiator doesnt work as efficiently.

 

Also to help out with the extra strain of turning the compressor.

 

So my aux fan turns on when I kick the AC on so maybe the temp sensor?

 

Ok, the fan's working good so lets start over. Have you noticed a pattern of when it overheats (other than turning the ac on), like slow moving or at highway speeds?

 

is the fan shroud in place? is the elec fan original or aftermarket can you hear it running when its on or do you just see it moving, that fan hauls *** you should be able to hear it.
my 98 does this in traffic, i have no shroud around the engine driven fan and i replaced the ori elec fan with a cheepo off ebay and it has no shroud either so i just ordered the ori. shroud for the engine fan and the correct elec fan both for less than 100. bucks shipped. all i have left is to tear the dash out and replace the heater core and evap coil lol

 

Both shrouds are on correctly. But here's something I thought of, I had thought my temp gauge didn't work but my temp sending unit wasnt plugged in and in wondering if it's just bad cuz when it redlines it doesn't smell hot and still runs ok.

 

If you have access to an Infrared Temp Gun would be an easy way to tell if its actually running hot.

And when mine ran up to 250° on the highway one day it ran fine too, so i wouldn't trust that.

I'm sure you've done this already, but have you checked the coolant level?

 

Yea coolant level was the first thing I checked

 

just because the radiator doesnt leak doesnt mean that its fine... biggest cause of overheating on XJ's these days... our xj's are getting old... most radiators if original have some sort of internal corrosion... cause it not to flow as well as original... i just replaced my water pump, hoses, radiator, and currently have no thermostat (housing kept leaking with one installed), and replaced my mechanic fan with another oem electrical fan... i run all day long at 150... lol... offroad i do 190 or so maybe... also when i offroad i turn my fans to come on at 180 to make sure things stay cool... AND mines a renix... radiators the big difference... pumps dont matter when cooling unless the blades are gone or shaft is sheered... hoses dont matter... u already changed the thermostat (dont recommend running without one by the way) so that leaves your radiator and/or clogged exhaust system... id replace the radiator... $100 brand new shipped on ebay...

 

oh and if fluid level were goin down id say check the cap as well but u said fluids good so i dont see that being your issue