Air conditioner from hell (1 Viewer)

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Joined
Dec 7, 2020
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2
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33
Location
Canyon lake texas
My baby is a 94 3x locked fj80 but she is causing me some grief right now. I am really hoping someone can help. I have searched mud and all the rest of the internet but have found nobody with my problem. For some reason with the a/c on if it's cool outside the a/c for blow for a bit and then the heater will come on and I get 140 degrees out of the vents. I was thinking ambient air temp sensor (apparently 94 landcruiser doesn't have) or cabin air temp sensor (apparently only in units with climate control). Any ideas will help even if they are bad/stupid. I live in texas so 9 months out of the year you really don't want your car deciding what temperature you should be.
 
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I'm not an AC expert. But it sounds like borderline low pressure. When cool, there isn't enough system pressure to run, when hot there's enough pressure to run. Refrigerant pressure is dependent on ambient temperature.
You really need to get a set of gauges on the system and see what they tell you. Then follow the above diagnostics chart.
 
View attachment 2732067

I'm not an AC expert. But it sounds like borderline low pressure. When cool, there isn't enough system pressure to run, when hot there's enough pressure to run. Refrigerant pressure is dependent on ambient temperature.
You really need to get a set of gauges on the system and see what they tell you. Then follow the above diagnostics chart.
I thought that too, checked refrigerant with one of the cheezy can gauges and it came out good but I plan on hooking up real gauges. The heater coming on is what vexes me. Does anyone know whether the heat slider goes straight to the heater control valve or does it hook to something that then operates hcv? I am dreading tearing apart dash to find out so hopefully a big brain on mud can tell me
 
I thought that too, checked refrigerant with one of the cheezy can gauges and it came out good but I plan on hooking up real gauges. The heater coming on is what vexes me. Does anyone know whether the heat slider goes straight to the heater control valve or does it hook to something that then operates hcv? I am dreading tearing apart dash to find out so hopefully a big brain on mud can tell me
If someone installed the wrong year heater control valve, it may be actuating backwards. The 91-92 version move the opposite direction, but will bolt in the same place.

This shouldn't be an "automatic" thing because the 94 doesn't have a temp control unit on it, you have to monitor that manually. It just may be that one is overcoming the other at that point.

Or, you have an actuator on a vent door that's either sticking or not functioning.

Check your fresh air VS recirculate modes as well.
 
If someone installed the wrong year heater control valve, it may be actuating backwards. The 91-92 version move the opposite direction, but will bolt in the same place.

This shouldn't be an "automatic" thing because the 94 doesn't have a temp control unit on it, you have to monitor that manually. It just may be that one is overcoming the other at that point.

Or, you have an actuator on a vent door that's either sticking or not functioning.

Check your fresh air VS recirculate modes as well.
I have tried recirculate vs fresh air...same same. I have been running a/c and heat on this thing perfectly for the last year and just within the last 2 weeks it has started acting up. One second it is blowing at between 34 and 60 degrees and a few seconds later it is blowing at 140 with an ambient temp of around 75 so it seems to me like SOMETHING is telling the heater control valve to open. I agreed with your comment on the possibility of the vent door so this morning I sent my girlfriend with a meat thermometer stuck in the vent and had her watch it.
 
Not on models without automatic climate control. So for yours, no.

Unless you have visual proof that the actuator is moving by itself, you should start with gauge readings and follow the chart posted above by @Rusty Marlin
I will put gauges on it but I don't believe that will be my problem.. that being said you have given me an idea, I will disconnect the cable from the heater control valve to see if a/c still switches to heat.
 
A bad expansion valve will make it blow hot through the vents because there will be HOT liquid refrigerant passing through the what is normally the evaporator.
But the only way to tell is through the gages and see what the pressures read. It falls under High side High, Low side Low.
Good idea pulling the cable off the heater valve.
 
That's what we do, you provide the rabbit, we start digging holes...goodness knows how far this rabbit hole goes...
 
That's what we do, you provide the rabbit, we start digging holes...goodness knows how far this rabbit hole goes...
When I figure out what it is I will post the answer because this is one of the few questions I never saw posted or answered in days of searching
 
That's what we do, you provide the rabbit, we start digging holes...goodness knows how far this rabbit hole goes...
On your post about the gauges I saw something in your attachment about earth ground...even tho that doesn't seem to be temperature associated it is another avenue I want to check
 
I fixed the AC on my '94 with a new expansion valve. Be sure to run the troubleshooting steps first to verify what it is.

Another wild idea I have is that you might have a failing heater valve? I doubt that would be intermittent.

You can easily see if the heater valve is being moved without your input by watching it under the hood. It's high on the firewall near the center.
 
"how far this rabbit hole goes..."

My 80's AC compressor started making some noise recently and I'm going to replace it. Because I don't want to deal with opening the system more than once, etc. I'm replacing pretty much everything but the hard lines and plan to have a clean and empty system that's easy to fill/charge when I'm done. The rabbit hole may go a bit further but that's a good stopping point for me as the rest (blower motor, controls, etc.) are easy to replace without splitting the system and needing to recharge it. All in the parts are $590. I'll buy R134 locally and use gauges/vac pump from a local auto parts rental deal on the cheap :) I've got an air compressor to help with blowing out the lines and mud has supplied a wealth of guidance from folks like @Rusty Marlin , @flintknapper etc. etc.

So, if you are running an og evaporator along with other high-mileage components I'd consider a similar approach as the clock is ticking on some of the system components. If you do end up being low on R134, it had to leak out somewhere... You can probably get by replacing lot less but you may have to try a few times to get reliable AC.

Note, some of the following may be cheaper on other sites or by different manufacturers/etc...

nylog for all fittingsnylogAmazon product ASIN B008HOSQQQ
 
images (3).jpeg
 
"how far this rabbit hole goes..."

My 80's AC compressor started making some noise recently and I'm going to replace it. Because I don't want to deal with opening the system more than once, etc. I'm replacing pretty much everything but the hard lines and plan to have a clean and empty system that's easy to fill/charge when I'm done. The rabbit hole may go a bit further but that's a good stopping point for me as the rest (blower motor, controls, etc.) are easy to replace without splitting the system and needing to recharge it. All in the parts are $590. I'll buy R134 locally and use gauges/vac pump from a local auto parts rental deal on the cheap :) I've got an air compressor to help with blowing out the lines and mud has supplied a wealth of guidance from folks like @Rusty Marlin , @flintknapper etc. etc.

So, if you are running an og evaporator along with other high-mileage components I'd consider a similar approach as the clock is ticking on some of the system components. If you do end up being low on R134, it had to leak out somewhere... You can probably get by replacing lot less but you may have to try a few times to get reliable AC.

Note, some of the following may be cheaper on other sites or by different manufacturers/etc...

nylog for all fittingsnylogAmazon product ASIN B008HOSQQQ
My last case will be replacing the whole system....I really hope I don't get to last case
 

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