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WaterH

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Ok, this is somewhat embarrassing because I'm somewhat of an AC expert. I maintain walkin freezers and coolers at our restaurant. Also the AC there. I have all the good quality tools and equipment for working on refrigeration stuff. I have an EPA license to buy freon. Most of my experience is not on auto, but the theory is the same.

Im working on my 90' Bronco. It was originally R12 converted to 134A years ago. It works, but I've never really been happy with it. Recently something went through the grill and put a hole in my condenser. So I got a new condenser, dryer and orface. Blew everything out, put a good vacuum on it and refilled with new freon.

It works, but I'm not happy with it. We have a newish Vette and the temp at the vent is 48 degrees in a matter of seconds after startup. (95 outside) It gets colder if you drive down the road. We have a beater PT Crusier that will blow 52 degrees pretty quick. My Bronco doesn't go below 60 no matter what. It does blow lots of 60 degree air and it will cool the truck after 5-10 minutes, but why so warm?

I kind of determined to get it working better. I pointed a lazor temp at the receiver/dryer and got 52 degrees. That reciecer is after the evaporator. So why is it colder than the vent air? I pulled the evaporator and cleaned the fins. It wasn't really dirty, but I thought it might help. No joy.

At this point, I'm thinking of replacing the evaporator. Right now everything is new except the evaporator and the compressor. The gauges show the compressor is working, so I don't really see how it could be the problem. When I google evaporator problems, all I get is leaks. Mines not leaking. Have any of you had one clogg up where it doesn't work?

Am I missing something else?
 

BJS

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there are two orifice tubes for the ford trucks one for r12 and one for 134a. Makes a world of difference in the performance on a converted system. Don't remember off the top of my head which is which though.
 

ThePanzerFuhrer

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there are two orifice tubes for the ford trucks one for r12 and one for 134a. Makes a world of difference in the performance on a converted system. Don't remember off the top of my head which is which though.

I was gonna say check if you have the right orfice tube installed.
 

Jason4x4

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Pinch off the heater hoses and see if the temp drops.
 

Tiha

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try blowing air across the condenser or running water over it. If that helps then yes fan clutch or plugged condenser.

It is normal to lose 10 degrees between the evap and vent outlets. Maybe not normal but within spec.

Also, is there flow through the heater core? Buy a bypass valve like used in the mid 90s cherokees, they have 4 hose barbs and completely bypass the heater core. Keep that heat out of the box.

Another trick is to adjust the pressure cutout switch so it doesn't kick off till about 10ps, maybe 5. Helps keep the pressures down and everything lasts longer.
 

WaterH

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fan clutch

I converted to E-fans a long time ago. They helped at idle.

there are two orifice tubes for the ford trucks one for r12 and one for 134a. Makes a world of difference in the performance on a converted system. Don't remember off the top of my head which is which though.

I have the orface tube for 134A. I also tried a "variable" orface tube. Someone on another forum said they were great. Didn't notice any differnce, so I went back to the fixed tube.


It's a thought. I would have to convert back. (Not a real big deal.) The issue is I have rode in other Broncos of the same period that would freeze you out. Why doesn't mine?

Pinch off the heater hoses and see if the temp drops.

I have a bypass valve on my heater hose.

One thing I was wondering. I have headers. They are real close to thebox where the evaporator is. The air that goes through the evaporator immediately hits a plastic piece that turns it into the cab. It's like 6" to the headers from the plastic piece. This is stock. Has anybody covered that plastic with some kind of aluminum?
 

WaterH

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try blowing air across the condenser or running water over it. If that helps then yes fan clutch or plugged condenser.

It is normal to lose 10 degrees between the evap and vent outlets. Maybe not normal but within spec.

Also, is there flow through the heater core? Buy a bypass valve like used in the mid 90s cherokees, they have 4 hose barbs and completely bypass the heater core. Keep that heat out of the box.

Another trick is to adjust the pressure cutout switch so it doesn't kick off till about 10ps, maybe 5. Helps keep the pressures down and everything lasts longer.

Condenser is brand new.
Has E-fans that work great.
Heater is bypassed.

What pressure switch are you referring to? 10 psi? The system runs over 40 psi on the low side.
 

dave_dj1

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Are the blend doors in their respective positions? Also isolate the heater core as stated above.
 

welndmn

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Is this driving or sitting? Older cars do not perform as well as newer cars in traffic like conditions, I have always added an electric fan and relay just for the A/C to blow more air over the condenser when idling in traffic.
 

Foxmxrcer

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Stupid question, did you put the proper amount of 134a in? I can't recall the formula... But it's like 85% of the r12 capacity or something.

Does the compressor cycle? What's your high side and low side pressures? They can tell you a lot about what going on....


Edit:

(R12 capacity X .9) - .25lbs = r134a capacity
 
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WaterH

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Are the blend doors in their respective positions? Also isolate the heater core as stated above.

Well, the AC works in normal and it increases in max. So I guess they work OK. Heater is bypassed.

Is this driving or sitting? Older cars do not perform as well as newer cars in traffic like conditions, I have always added an electric fan and relay just for the A/C to blow more air over the condenser when idling in traffic.

I have good working E-fans.
 

M92PV4U

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I converted to E-fans a long time ago. They helped at idle.



I have the orface tube for 134A. I also tried a "variable" orface tube. Someone on another forum said they were great. Didn't notice any differnce, so I went back to the fixed tube.



It's a thought. I would have to convert back. (Not a real big deal.) The issue is I have rode in other Broncos of the same period that would freeze you out. Why doesn't mine?



I have a bypass valve on my heater hose.

One thing I was wondering. I have headers. They are real close to thebox where the evaporator is. The air that goes through the evaporator immediately hits a plastic piece that turns it into the cab. It's like 6" to the headers from the plastic piece. This is stock. Has anybody covered that plastic with some kind of aluminum?

My dad's 89 blazer full size will freeze you out but it's got r12.
 

WaterH

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Stupid question, did you put the proper amount of 134a in? I can't recall the formula... But it's like 85% of the r12 capacity or something.

Does the compressor cycle? What's your high side and low side pressures? They can tell you a lot about what going on....


Edit:

(R12 capacity X .9) - .25lbs = r134a capacity

Not stupid. Very common. But I have tried the proper amount, more than the proper amount and less than the proper amount. Slightly more than the proper amount seemed to be best. I got 40-50 low side and 200-250 high side. (Around 95 degrees)

Not sure about capacity because I have a condenser from a newer Bronco (134a) Not sure if it increases or decreases capacity.
 

Foxmxrcer

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Not stupid. Very common. But I have tried the proper amount, more than the proper amount and less than the proper amount. Slightly more than the proper amount seemed to be best. I got 40-50 low side and 200-250 high side. (Around 95 degrees)

Not sure about capacity because I have a condenser from a newer Bronco (134a) Not sure if it increases or decreases capacity.

Does the compressor cycle a lot? I think those trucks had the thermal probe on the low side like my w250. Or was it attached to the evaporator? Either way, if it has it, you can play with is location/depth to fine tune the temperature output. Just don't make it too cold, or it'll freeze up.
 

WaterH

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Does the compressor cycle a lot? I think those trucks had the thermal probe on the low side like my w250. Or was it attached to the evaporator? Either way, if it has it, you can play with is location/depth to fine tune the temperature output. Just don't make it too cold, or it'll freeze up.

Doesn't hardly cycle at all. (At least when it's hot out) I'm not aware of a probe. (Doesn't mean anything) I thought it cycled by pressure switches alone. I guess I need to research.
 
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based on my reading the AC performance on the OBS leaves a lot to be desired. Also electric fans move less CFMs then the OEM mechanical.

i will have to check my bronco and f150 with a temp gun and see what i am getting
 

WaterH

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based on my reading the AC performance on the OBS leaves a lot to be desired. Also electric fans move less CFMs then the OEM mechanical.

i will have to check my bronco and f150 with a temp gun and see what i am getting

My E-fans definitely were an improvement over stock at idle. No differnce down the road. Not sure if you can use a temp gun at the vents. But you could point it at the accumulator. Mine was reading 52 there.
 

Foxmxrcer

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Doesn't hardly cycle at all. (At least when it's hot out) I'm not aware of a probe. (Doesn't mean anything) I thought it cycled by pressure switches alone. I guess I need to research.

I may be mistaken, I'm stretching my brain to remember their setup. But I vaguely recall them having a temp sensor for the evaporator.
 

SLOWPOKE693

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based on my reading the AC performance on the OBS leaves a lot to be desired. Also electric fans move less CFMs then the OEM mechanical.

i will have to check my bronco and f150 with a temp gun and see what i am getting

My OBS Ford will freeze you out of the truck if I drive around with it on high. And I'm in Texas where its hot, hot.
 

Tiha

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No temp sensor in the evap.

Low pressure cutout switch on the drier.

That low side pressure is kinda high.

There are equations to estimate charge, but the proper charge is when the inlet and outlet of the evap are the same temperature.
 

WaterH

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I may be mistaken, I'm stretching my brain to remember their setup. But I vaguely recall them having a temp sensor for the evaporator.

They don't show one in the diagram at LMC truck. In my research, it appears they have them on later Ford trucks. (Like 2005)
 

WaterH

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No temp sensor in the evap.

Low pressure cutout switch on the drier.

That low side pressure is kinda high.

There are equations to estimate charge, but the proper charge is when the inlet and outlet of the evap are the same temperature.

That's interesting. My AC multi-meter has a temp probe. Of course, I just broke it working on something else. I guess I need to order another..
 

Tiha

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What engine rpm are you taking your temp and pressure readings at?

ideally 1200-1500 rpm.

And you are trying to cool a big cabin, but any AC system should put out vent temps 30 degrees below ambient. From the factory they were designed to only be 20 degrees below ambient.
 

WaterH

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What engine rpm are you taking your temp and pressure readings at?

ideally 1200-1500 rpm.

And you are trying to cool a big cabin, but any AC system should put out vent temps 30 degrees below ambient. From the factory they were designed to only be 20 degrees below ambient.

I have a plate that holds the rpms up alittle higher than idle. (Maybe 1100-1200)

I realize the cabin will take some time to cool, but the vent temp never gets below 60. My wife's Vette will put out 48 degrees almost immediately.
 

Tiha

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I agree I had an 84 suburban that put out 38 in the rear and 42 in the front after conversion so yeah R12 isn't better just easier with lower pressures.

I usually use the cheapy IR thermometer from HF. Close enough.

You can also try slowing your blower down a notch and see what that does to vent temps. If the EVAP is just too small you might be moving air across it too fast. Those old fords moved a lot of air.
 

BIG-O

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134a converted vehicles never worked as good because the condenser is too small.
 

WaterH

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So has anyone had a new evaporator make a differnce? I'm talking about one that was internally plugged. (Not replaced for a leak) I know Fords are famous for the "Black Death" (when compressor fails, sends black shit all through the system) I've always heard it plugs up the condenser or the orface. I don't really see how it would get to the evaporator. But I'm grasping at straws.
 

Tiha

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I have been doing AC work on cars since 1984 and I have never seen an evap too dirty to clean inside or out.
haven't even seen that many leak either
But then that is just my experience.

I would be curious if it made a difference for ya.

Only one that comes to mind was an early 90's ford that was 134 from the factory. It constantly iced over the evap. It pretty much had to be the evap, either an external restriction in air flow through it, or an internal restriction. Owner did not want to replace it, he just ran over charged to prevent the problem. In a little standard cab pickup it doesn't take much to keep it cool it didn't need to be perfect like you trying to cool a whole bronco.

You know, you got me thinking though, there was an 88 or 89 F350 I did and it had this little brass fitting in the high pressure line, like a throttle valve or something, can't remember what they called it, but it was a head of the orifice tube near the radiator support. That was wrecking havoc with pressures and temps. That system never was all that great, I don't remember the temps we got, but I do remember at that time reman compressors were junk and new ones were $700 so we had to do the best we could with the crappy reman. We tried a few alternative R12 products but in the end the R134 worked as well and was a lot cheaper.
It would not pump worth a crap at idle.
 
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