Searched And Searched...AC Not Freezing, Heat Not Hot

TPI Monte SS

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Hey all,
Long time member here, haven't posted in quite a while because my son took over my wife's KJ about 2 years ago. It's had it's share of repairs that we've tackled in the last few years, but all have gone smoothly and we haven't really needed to consult the gurus here...the Search function gave us the answers we needed. This most recent problem started over the winter, is now continuing into the summer, and frankly, we're stumped.

A few years back, we replaced the radiator, water pump, thermostat, and hoses. All went well, and the heat was typical Jeep "melt your face off" heat. Over this past winter, the heat was just ~meh~....kinda warm, not super hot like it used to be. We replaced the thermostat again, bled the system, and it was still just warm. He checked it on the Scantool at school, and it was operating around 195*, so it should have had hot heat. Anyway, he lived with it and bundled up.

Now the summer is coming, and with the first few warm days we've had, he also discovered the AC is not the usual "freeze your a$$ off" cold that it used to be. The compressor is cycling on and off, and there's a few second pause between cycles, which seems normal. It does not run for very long, which makes me think the AC system thinks we're only looking for "kinda cold", not "meat locker" temperatures. IMO there's something wrong with the temperature control that's not allowing it to go to full hot or full cold, but what is it??

We searched the forum for suggestions - his KJ is an early '03 model (we bought it in September of '02), so the reset procedure for the temperature control unit did not help. We found two vacuum diaphragms under the dash on the driver side - we unplugged the red/brown vacuum lines going to the upper one and discovered it controls the blend door for vent/defroster. Everything there switches normally. Then we unplugged the blue/yellow vacuum lines going to the lower diaphragm and noticed no change at all. I'm assuming that one is related to temperature, but the FSM is not really clear on how it operates with the rest of the system.

So, anyone have suggestions? Could that diaphragm have failed and be causing the temperature issue? Or something else you all are aware of that we should look at?

Thanks in advance, hopefully someone out there in KJ-land can point us in the right direction!
 

DadOSix

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Hey all,
Long time member here, haven't posted in quite a while because my son took over my wife's KJ about 2 years ago. It's had it's share of repairs that we've tackled in the last few years, but all have gone smoothly and we haven't really needed to consult the gurus here...the Search function gave us the answers we needed. This most recent problem started over the winter, is now continuing into the summer, and frankly, we're stumped.

A few years back, we replaced the radiator, water pump, thermostat, and hoses. All went well, and the heat was typical Jeep "melt your face off" heat. Over this past winter, the heat was just ~meh~....kinda warm, not super hot like it used to be. We replaced the thermostat again, bled the system, and it was still just warm. He checked it on the Scantool at school, and it was operating around 195*, so it should have had hot heat. Anyway, he lived with it and bundled up.

Now the summer is coming, and with the first few warm days we've had, he also discovered the AC is not the usual "freeze your a$$ off" cold that it used to be. The compressor is cycling on and off, and there's a few second pause between cycles, which seems normal. It does not run for very long, which makes me think the AC system thinks we're only looking for "kinda cold", not "meat locker" temperatures. IMO there's something wrong with the temperature control that's not allowing it to go to full hot or full cold, but what is it??

We searched the forum for suggestions - his KJ is an early '03 model (we bought it in September of '02), so the reset procedure for the temperature control unit did not help. We found two vacuum diaphragms under the dash on the driver side - we unplugged the red/brown vacuum lines going to the upper one and discovered it controls the blend door for vent/defroster. Everything there switches normally. Then we unplugged the blue/yellow vacuum lines going to the lower diaphragm and noticed no change at all. I'm assuming that one is related to temperature, but the FSM is not really clear on how it operates with the rest of the system.

So, anyone have suggestions? Could that diaphragm have failed and be causing the temperature issue? Or something else you all are aware of that we should look at?

Thanks in advance, hopefully someone out there in KJ-land can point us in the right direction!
A few toughts Steve -

since both conditions exist - i suspect the blend door is binding.

the door exists to move along with the blue to red temperature dial.

blue is 1 extreme. Moving along, the door allows air to mix to the desired tempertaure. Red is the other extreme - full on hot. The door swings about 90 degrees.

that above all assumes that both the heater core and evaporator core are getting what the need to make heat and cold.

from what you describe, as a starter, your kj could need a boost of refrigerant. Without a gauge set or observation of the jeep in cool cycle, it is hard to tell.

no / low refrig - compressor clutch will not engage.

enough refrig to,satisfy the low pressure switch - compressor engages but short cycles as the compressor suction increases. Like 15-30 seconds on /off /on / off.

good refrig - compressor engages and cycles normally - on - runs a bit (minute - or so depending on ambient temp ) cycle off til need for cool. Jeep actually gets cool.

restricted orifice tube - plenty of refrig, but cant ' evaporate the refrig' thru the coil to cool the jeep.

what do,your ac lines look like? Hot? Sweaty? Frosted over ?

that service manual details pretty well the blend door and mode door operation - section 24.

best to diagnose both issues before tearing into the dash because it if a lot of work to get it out.

on the heat side - clogged heater core - clogged supply lines - bad water pump / impeller / stat.

all this thinking is just what i'm goung to be doing when my 04 kj comes home. #2 son has her at college and it has no ac at present.

see what you can see and let's solve this thing.
 

LibertyTC

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Yes it could be a blend door issue, check to ensure the accumulator is staying cold.
Set to re-circulation mode, the electrical fan should be turning continuously, if the jeep is at normal operating temperature.
 

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TPI Monte SS

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Thanks for the responses - sorry I didn't post sooner with an update!

My son is currently attending auto tech school and working part time at a shop. One of the mechanics there gave it a boost of refrigerant and now it's cold. For some reason, the shop doesn't have gauges so we're not sure ~how~ full it is, but the AC lines are sweaty and cold, so that's good. We haven't had to charge it in 20 years, so I guess it was due LOL.

As of now, I can hear the blend door switching in the dash, so I'm thinking it might be alright for now. We'll wait until it gets colder before we worry about it.

Looks like I'm going to be more active again on the forum; just today the Airbag light came on, so that'll be the next thing we have to diagnose. Ugh! We took it some years back to have the Airbag recall taken care of, and haven't had any issues until today.
 

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