A/C Help
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Cross-Country
Joined: Apr 2009
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From: Fort Smith Arkansas
A/C Help
I have a 1981 F150 4x4 with a 351M and a C6 tranny.
I just put a new compressor on and flush out all the lines, replaces the orifice tube, replaced all seals/o-rings and line filters. Ran a vacuum on the system, it held a -25 vacuum for about 30min. So i charged the system first with 3oz of ester oil, then 2.5oz die shot/oil mix. Then put five 12oz cans of r134a (which if i did my math right should be 3lb-12oz) which is what my sticker on the front of my truck says it takes. I put my gauges on it: Low side about 40, High side about 155. My problem is that my compressor is not cycling, it is staying on constantly (getting extremely hot) What could be causing this? I have two electrical wires running on one of the hoses to the compressor, one hooking up to the compressor clutch and the other isn't connected to anything, could this be the problem? Below is a picture:
I just put a new compressor on and flush out all the lines, replaces the orifice tube, replaced all seals/o-rings and line filters. Ran a vacuum on the system, it held a -25 vacuum for about 30min. So i charged the system first with 3oz of ester oil, then 2.5oz die shot/oil mix. Then put five 12oz cans of r134a (which if i did my math right should be 3lb-12oz) which is what my sticker on the front of my truck says it takes. I put my gauges on it: Low side about 40, High side about 155. My problem is that my compressor is not cycling, it is staying on constantly (getting extremely hot) What could be causing this? I have two electrical wires running on one of the hoses to the compressor, one hooking up to the compressor clutch and the other isn't connected to anything, could this be the problem? Below is a picture:
Logistics Pro
Joined: Jan 2007
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From: Martinsburg, WV
What is your center vent temp and the current outside(ambient) temp, are these pressures at idle? fan speed, recirc? The extra wire should have gone to a solenoid that would idle up the motor a few hundred rpm's to compensate for the compressor running. At that lowside pressure the compressor will stay running, it wont cycle until ~20ish. Also what do the pressures do at say 18-2200 rpm?
Also, what color o-tube did you put in?
Also, what color o-tube did you put in?
Last edited by Archion; Mar 23, 2012 at 01:53 PM. Reason: for more info
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Cross-Country
Joined: Apr 2009
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From: Fort Smith Arkansas
Ill have to check the pressures at those RPM's, isnt the low side and high side suppose to be around 40psi and 155psi? Or is it different on these older trucks? Also where is this solenoid, do i still have one or are they often removed?
Logistics Pro
Joined: Jan 2007
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From: Martinsburg, WV
The solenoid should be on the carb originally, where it could actuate the throttle. They do get removed as some people didn't know what they were and ripped it off with the emissions etc... Average knee-jerk redneck response of " don't know what it is, so I don't need it" has done a number on these older trucks over the years. The pressured are pretty good for average operation, I just like mine a bit colder=lower low side. That's why I asked what O-tube you put in. Also check to make sure the condenser is clean and you fan/clutch/shroud are in good order.
Last edited by Archion; Mar 23, 2012 at 03:37 PM. Reason: spelling and content
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Cross-Country
Joined: Apr 2009
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From: Fort Smith Arkansas
Here is the orifice tube i put in, not sure that the difference was in all them when i bought it so i just went for the cheaper one.
Buy Factory Air Orifice Tube 38621 at Advance Auto Parts
Buy Factory Air Orifice Tube 38621 at Advance Auto Parts
Logistics Pro
Joined: Jan 2007
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From: Martinsburg, WV
Ok, the blue tube is the stock tube for r-12 on your truck, I would have gone with the orange tube, but it will still work. It's just that R134a is less dense than R12 and works at slightly different pressures and works better with a smaller orifice on retrofits. The best way is to start with 80% of OE charge and work up till it's the best mix of pressures and temps. If you actually have too much in the system it can make it run warm. It's a bit of a fine line. If you look at the temp scale on your guages, that can be used as a theoretical temp at the evap for fine tuning purposes. If you have the large two wire pressure switch on the accumulator, that can be adjusted as well to lower the cutoff pressure slightly.
Old School Hot Rodder
Joined: Feb 2006
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From: Exmore, VA
155 on the high side is probably a little low for R134a, mine runs up around 225-250, but low is right around 30 at idle. I have the red tube in mine since it's a crew cab.
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Cross-Country
Joined: Apr 2009
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From: Fort Smith Arkansas
Okay from all the info you have given me i think i have figure it out, wrong orifice tube, not enough freon and also i think my clutch cycling switch is either for R12 or is bad. So i run into a problem, i have about $100 of freon in the system, i do not have a recovery system. All i have is a vacuum pump, an empty 33lb freon bottle and a set of gauges. My question is, can i run a vacuum on a 33lb freon bottle and suck the freon out this way, if so how much of a vacuum do i need to pull on the tank. Or does anyone else have any ideas? I did purchase an orange orifice tube and a new clutch cycling switch.
Logistics Pro
Joined: Jan 2007
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From: Martinsburg, WV
None of us ever said you had too little in the system. 3 3/4 pounds is what you have. What we noticed is that you have a high side pressure that is ~50-100 psi down from where it should be. This could be from a failing compressor, a restriction in the system, or not enough charge as you said. That's why I asked what the temps were. If you are taking the system back down, and you did not do it before, replace the accumulator, it's like a filter. If it's soaked a fair amount of water it can throw things off as well.
Old School Hot Rodder
Joined: Feb 2006
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From: Exmore, VA
Not to mention, unless it is a new accumulator, the dessicant is not compatible with R143a. It will most likely come apart and give you real problems.
One of the things with AC systems, insufficient charge does not give you enough liquid refrigerant causing high temperature at the compressor. I can watch one when I charge it, the pressure on the low side will start low, climb up gradually, then drop again when you start approaching the correct level. High side will be low as the refrigerant is literally blowing through the orifice until enough liquid builds up. Once you start to get enough liquid, it will climb fairly high, then as you get the proper level it will actually drop.
Temperature readings are really the only good gauge of proper charge, inlet and outlet of the evaporator should be very close and your accumulator should be cold about 1/2 way up at low blower recirc. The still evaporating refrigerant is what keeps the compressor cool. The high side will get quite hot even when everything is right.
One of the things with AC systems, insufficient charge does not give you enough liquid refrigerant causing high temperature at the compressor. I can watch one when I charge it, the pressure on the low side will start low, climb up gradually, then drop again when you start approaching the correct level. High side will be low as the refrigerant is literally blowing through the orifice until enough liquid builds up. Once you start to get enough liquid, it will climb fairly high, then as you get the proper level it will actually drop.
Temperature readings are really the only good gauge of proper charge, inlet and outlet of the evaporator should be very close and your accumulator should be cold about 1/2 way up at low blower recirc. The still evaporating refrigerant is what keeps the compressor cool. The high side will get quite hot even when everything is right.