Overheating only with A/C on

I've run into this as summer kicked in this year, last summer I had no issues at all. In 109* heat I can idle for extended periods, sit in stop and go traffic or run on the highway with no sign of over heating at all.

With the A/C on however I will go from 210 to 230 very quickly in any condition. I can turn the A/C off and the temp will drop right back down to 210 in a few minutes.

The A/C seems to blow cold, I haven't used it hardly because of this problem. I did idle it in my garage with the A/C on when checking the refrigerant level and it was blowing ice cold there.

I've been searching and some people suggest the E-fan isn't hitting it's 2nd speed, I didn't know it had 2 speeds. Others suggest the thermostat is sticking or the A/C condenser is clogged. Is there a way to test the condenser or fan? Or anything else to check?

Just so weird to me that the temperature jumps so much so fast with the A/C and as soon as the A/C is off it cools right back down. That makes me think the cooling system is fine and it's got to be an e-fan or condenser issue.

I have a CFM 3 row radiator, hesco water pump, HD ZJ fan clutch, OEM thermostat, OEM radiator cap, OEM lower hose with spring, E-fan is kicking on and staying on and coolant level full with proper mix.

I am gonna go out on a limb here and say something else is going on

are you certain the temp it right?

X2 I think the temp sensor may be giving a false reading?

I actually just replaced the temp sensor but I can't rule it out. I will try to drive and get it hot and use my IR temp gun to get another reading. Is there a certain spot I should get a reading at other than the thermostat housing?

If the cooling system is still all OEM I would say that the electric fan is not coming on. The electric fan should come on when the AC compressor is running as well as when the engine temperature reaches a pre-determined range. And by-the-way the electric fan is single speed.

techno1154 said:

If the cooling system is still all OEM I would say that the electric fan is not coming on. The electric fan should come on when the AC compressor is running as well as when the engine temperature reaches a pre-determined range. And by-the-way the electric fan is single speed.

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iwannadie said:

E-fan is kicking on and staying on

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As mentioned, the e-fan comes on and stays on. I should have said that it comes on when the A/C is turned on and I can hear it kick on when my temp goes up also.

What year is your pos? When the A/C is on, the condenser in front of the radiator sheds heat. The heat doesn't usually transfer into the coolant though, so it would be useful to know where the temperature is being monitored (97+ would show the temperature at the tstat housing, which picks up ambient temperature more than the 96- design).

The other question is why the heat isn't being evacuated. The electric condenser fan is supposed to come on whenever the A/C is activated (it only has one speed setting) or when the CTS in the tstat housing (assuming 91+) exceeds about 220f (give or take a couple of degrees). If the fan isn't coming on the heat would just kind of sit there at the condenser and would eventually cause the coolant in the radiator to get hotter, so first thing is verify that the fan comes on with the A/C. Another thing to try is go pressure wash the condenser and radiator; any junk in the fins will restrict airflow which will impede the ability to transfer heat.

The heat does transfer into the coolant by the simple fact that the condenser pre-heats the air going across the radiator. The OP has stated that the Aux Fan is running while the AC is on.

OP, if you have access to a friend's XJ that is working correctly, borrow the Aux Fan and try that. I just had mine die a couple of weeks ago. The symptom was overheating with the AC on. As the Aux Fan was running intemittently, the extra heat being generated in the radiator was not being shed which caused the coolant temperature to spike. AC off, temps would drop down. Replaced the Aux Fan and all is well.

Heat transfer is hot-to-cold. The purpose of the secondary condenser fan is to provide a constant flow of cooler air for the heat to transfer onto. The air will be warm but if the car is warmed up then the air will still be cooler than the coolant in the radiator, so heat will still transfer from the radiator to the air, not the other way around. The only time the heat from the condenser should transfer to the coolant in the radiator is when the engine is cold (heat will transfer from warm air to the cold coolant), but he is talking about 210-230f so that is not the case here. If the air is hot and standing there then it will eventually impede the ability for heat to be transferred from the coolant in the radiator, but that generally means there is not enough airflow to evacuate the air. So either the fan doesn't work or the condenser and/or radiator are clogged.

ehall said:

What year is your pos?

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I always do that, I forget my POS info isn't in a signature that automatically shows and I feel stupid everytime.

97 country 4.0 auto 4x4.

o-gauge-steamer said:

The heat does transfer into the coolant by the simple fact that the condenser pre-heats the air going across the radiator. The OP has stated that the Aux Fan is running while the AC is on.

OP, if you have access to a friend's XJ that is working correctly, borrow the Aux Fan and try that. I just had mine die a couple of weeks ago. The symptom was overheating with the AC on. As the Aux Fan was running intemittently, the extra heat being generated in the radiator was not being shed which caused the coolant temperature to spike. AC off, temps would drop down. Replaced the Aux Fan and all is well.

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I may try to barrow or just replace the fan. It turns on but I can't say it's spinning as fast as it should even though it sure looks fast.

I'll be following this thread, My 97 XJ is doing the exact same thing. I'm lead to believe that my Radiator may still be the OEM one due to the rusy color of my coolant.

I'm betting it's your condenser...

I spend time in AZ every year, usually during April/May and then again August/September.
I run your highways a lot when the bugs are out in force in spring & during the summer rains.

Before & after trips to your area I usually take the grill off to pick the bugs & gravel out and straighten fins with a dental pick before
soaking the condenser to soften-up what's left. After a few minutes soaking I try blasting out the deeper stuff with higher pressure.

I think it makes a very noticable difference... for a while, that is... before it eventually gets all jammed-up again.

Something worth considering, IMO...

I will pull the grill off and try to clean it out. Would I be able to use shop air from behind the radiator to blow stuff back out or will I need to try and get between the radiator and condenser? Being as I've never cleaned the condenser it sure to help some what at least.

iwannadie said:

I will pull the grill off and try to clean it out. Would I be able to use shop air from behind the radiator to blow stuff back out or will I need to try and get between the radiator and condenser? Being as I've never cleaned the condenser it sure to help some what at least.

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use a hose from behind to flush it all out.

Get it all wet, then spray it with a mild cleaner like simple green, let sit, hose from behind and watch the nasty come out. Don't use high pressure or you will damage the fins.

87manche said:

use a hose from behind to flush it all out.

Get it all wet, then spray it with a mild cleaner like simple green, let sit, hose from behind and watch the nasty come out. Don't use high pressure or you will damage the fins.

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Nate you just gave me something to do tomorrow. If that doesn't help, i'm ordering a radiator next week.

I am trying not to get my hopes up but I may have solved this. I decided to replace the radiator cap since it's only 4 bucks. I got a napa 16 lb cap to replace my dealer cap that is about 1 year old.

I ran the A/C today full blast for 20 minutes with no sign of over heating, it stay pegged at 210 in stop and go traffic. The only thing that has me still hesitant is that the temperature was only 91ish. When I was noticing the real problem recently it was well over 110, so we'll see but so far so good.

I'm a little lost on the radiator cap thing ... a lot of people have suggested it to fix overheating problems and just as many have had luck fixing problems with replacing it.

If the rad cap was bad, wouldn't it be spitting out coolant or making a bunch go into the overflow tank (non-renix) instead of causing overheating?

Miller88 said:

I'm a little lost on the radiator cap thing ... a lot of people have suggested it to fix overheating problems and just as many have had luck fixing problems with replacing it.

If the rad cap was bad, wouldn't it be spitting out coolant or making a bunch go into the overflow tank (non-renix) instead of causing overheating?

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That is why I am not holding my breath as it being the fix for me but I can't argue with the results currently.

The air is thinner than the water so it just leaks around the cap.The water isn't getting the pressure it needs to be pushed.