A/C line freezing over

HenikonLJ

HenikonLJ

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Washington
Something really strange happened this last weekend. While snow wheeling my heater and defrost was working just fine all day. Towards the end of the day we where all outside playing in the snow for like 15 mins the jeep was idling staying warm. When we all loaded back up went to turn it from defrost to vents so warm our hands and stuff up faster, and boom nothing. Blower motor still running but it was like the blend door stoped functioning.
Opened the hood to start tracing vacuum lines and seen this. I unplugged the pressure switch thinking it might keep the compressor from kicking on. After trying to trouble shoot the problem I gave up and we started heading back down the mountain, we had to stop for a guy in our group and while stopped I shut the jeep off. About 10 mins later I fired it back up and everything worked again no idea what happened and how I can prevent it in the future. Was thinking add a button so the compressor isn't running all the time but not sure that was even my issue to begin with.

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HenikonLJ said:
Would that cause the blend door to stop the vents from switching?
Click to expand...

Maybe.

I'd start with draining the AC, replace the receiver dryer...consider doing all the o-rings - they make kits, getting it flushed out, holding vaccum for a couple of hours...etc.

Might as well tackle the obvious.

-Mac
 
macleanflood said:
Maybe.

I'd start with draining the AC, replace the receiver dryer...consider doing all the o-rings - they make kits, getting it flushed out, holding vaccum for a couple of hours...etc.

Might as well tackle the obvious.

-Mac
Click to expand...

If I'm being honest I could care less about the ac. I live in the PNW. It's either cold and raining or nice enough to have the top off. I know the AC does more than blow cold air (drys the air) but I'm more worried about why the blend door just stopped working. I'm not well versed in this specific system but I can't see how the AC line freezing would stop functions from changing from defrost to vents and back. It was almost like when I switched it to vents it got froze halfway switching but it wasn't blowing air from anywhere. No foot/defrost/dash vents.
 
HenikonLJ said:
Would that cause the blend door to stop the vents from switching?
Click to expand...

It would cause it to stop blowing cold air until the ice blockage cleared and then resume working again after it cleared, like shutting off for a while. You probably need to have someone put some die into your AC system and check for leaks.
 
flyinfish said:
It would cause it to stop blowing cold air until the ice blockage cleared and then resume working again after it cleared, like shutting off for a while. You probably need to have someone put some die into your AC system and check for leaks.
Click to expand...

It never stopped blowing hot air. It stopped blowing any air from any vents.
 
From googling more stuff it looks like my blend door is electronic, but that's just for hot/cold I guess I'm not sure what exactly I need to search for as far as what the actuator would be called for switching modes.
 
My ac clutch is squeaking on my 97. Got a new compressor but haven't bothered to install it.

PNW I usually need the heater year round.

Could check the HVAC box holds vacuum... disconnect the line at the firewall and use something like a Mighty Vac with a gauge.

-Mac
 
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macleanflood said:
My ac clutch is squeaking on my 97. Got a new compressor but haven't bothered to install it.

PNW I usually need the heater year round.

Could check the HVAC box holds vacuum... disconnect the line at the firewall and use something like a Mighty Vac with a gauge.

-Mac
Click to expand...

Yeah heater year round is a must. Specially defrost 🤣.
I'll check vacuum but I traced all the lines and everything was good from the check valves through the firewall to the only vacuum actuated thing I could find which looked like it was the fresh air door. And that was still working while I was trying to trouble shoot the problem when it was happening. I'm not sure what else is vacuum actuated on the 05 model.
 
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HenikonLJ said:
Something really strange happened this last weekend. While snow wheeling my heater and defrost was working just fine all day. Towards the end of the day we where all outside playing in the snow for like 15 mins the jeep was idling staying warm. When we all loaded back up went to turn it from defrost to vents so warm our hands and stuff up faster, and boom nothing. Blower motor still running but it was like the blend door stoped functioning.
Opened the hood to start tracing vacuum lines and seen this. I unplugged the pressure switch thinking it might keep the compressor from kicking on. After trying to trouble shoot the problem I gave up and we started heading back down the mountain, we had to stop for a guy in our group and while stopped I shut the jeep off. About 10 mins later I fired it back up and everything worked again no idea what happened and how I can prevent it in the future. Was thinking add a button so the compressor isn't running all the time but not sure that was even my issue to begin with.

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Click to expand...

The evaporator was frozen causing no air to pass through. You could turn off the A/C for a bit to let the ice melt. This could be due to pressure switch not opening at the correct pressure or the a/c clutch relay sticking on.
The blend door is not vacuum operated it is electric.
 
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GaTechTJ said:
All air flows through the evaporator coil, regardless of vent position. If the evaporator core froze over, then there would be zero airflow.

Low freon charge can cause the evaporator coil to ice over

See this video for how the air flows in the box. TJ Heater airflow
Click to expand...

Okay this makes total sense. I was under the impression air would only pass over that when actually using the AC. Figured with the heater running it would be pulling fresh air from the fresh air vent over the heater core.
 
So I think the answer is evap core froze solid not allowing air to blow through. Thus blocking any vents from blowing. So the fix is check that the system is functioning correctly and install a switch to disable the compressor when it's not needed.
 
I'd check the freon level. If you don't want the AC compressor to run, pull the fuse or the relay. Both should be over the passenger side fender.
 
HenikonLJ said:
So I think the answer is evap core froze solid not allowing air to blow through. Thus blocking any vents from blowing. So the fix is check that the system is functioning correctly and install a switch to disable the compressor when it's not needed.
Click to expand...

Air passes through the evaporator to reduce moisture in the air and the is reheated by the heater core.
I have run into this many times with vehicles. What I have found is some system when at idle will pull the pressure down enough to freeze up but not enough to open the cycle switch. This may not be a concern at higher ambient temperatures or when the engine is off idle. I would let it idle till you see the line or dryer frosting over then raise the idle to see if the compressor disengages. If it does I wouldn’t worry about it, just turn it to a non-A/C mode when you encounter that cold long idle situation again.
 
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