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I have a Dodge Grand Caravan SXT 2007 that has no AC (w/

ATC). I have checked refrigerant...
I have a Dodge Grand Caravan SXT 2007 that has no AC (w/ ATC). I have checked refrigerant and blend doors and can't seem to find out what is wrong.
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Answered in 1 hour by:
7/15/2015
Dodge Mechanic: Jan Andersson, ASE Master Tech replied 7 years ago
Jan Andersson
Jan Andersson, ASE Master Tech
Category: Dodge
Satisfied Customers: 834
Experience: 20 years of automotive repair & modification, USA, Asian, Euro, old & new cars.
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Hi, Just to verify, how did you check the refrigerant? When you turn the Ac on, does the compressor clutch engage? I am guessing it doesn't. I would check the fuse and swap the AC Clutch relay with another relay of the same part number that doesn't affect the engine or anything else critical, like fog lamp or horn relay. How comfortable are you with using some basic test tools like voltmeter or test light? You could learn a lot from testing the pins under the Ac Clutch relay, you can short the battery power pin to the clutch pin to force the clutch to come on, if the battery pin has power. This is only for a very brief temporary test. You would need a jumper wire (Or thin needle nose pliers or tweezers) to jump pins/sockets number 30 and 87 together. If the ac compressor clutch still doesn't come on, it is probably bad, and you can proceed to testing it more closely. Sometimes they wear out and the electro-magnet inside is not strong enough to pull the clutch in for contact. A gentle push on the clutch center hub would then snap it in and it would stay engaged. If you do this, be very careful when it starts spinning, so the tool you used doesn't get caught up in anything and cause damage. I use a piece of pvc pipe or broom stick. If it catches on the clutch it can get kicked pretty good. Let me know how comfortable you are with these hands on tests, and if you have these simple testers
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Customer reply replied 7 years ago
Thanks for your response.I checked the low pressure side with my refrigerant gauges. ~100 psi when engine off, 29 to 32 when at idle, goes down to 15 to 20 when at high idle (~1500 RPM). I hear the clutch engaging and disengaging after running a few minutes and I see the pressure changes accordingly so I think the clutch and compressor are working. I also notice condensation falling out the bottom of the evaporators.This led me to check the blend doors and after exposing them they all seem to be "actuating" properly. I ran the service manual calibration procedure for the actuators and everything seemed ok. I also ran the A/C cool down test procedure, also from the service manual, and it seemed ok as well although I think I need to check if it threw a code. If it did, no notification light came on.I have no problem with simple electrical tests. I have a simple voltmeter that I can use. If you want me to move some relays around I would like you to be specific as this would be new to me. Give me a relay that I can swap so I don't screw something up. I have a wire with alligator clips on both ends that could be used to jumper something but I have never gone looking for the fuse box or relay box so I don't know if that would even work.I think I could handle most of your hands-on tests as long as I don't need highly specialized equipment. Give me your top one or two possible causes and I will track it down and report.
Dodge Mechanic: Jan Andersson, ASE Master Tech replied 7 years ago
Ok you are correct the clutch is working and the compressor is at least doing something, drawing the low side down. I think you are low on refrigerant though. At idle you are probably pretty close to the low pressure safety limit, and as soon as you give it gas, it draws the low side too low and the compressor clutch disengages. 15-20psi is very low for the low side, most systems cut off the compressor at around 25psi. its because the engineers figured its safer to cut it off than to let it starve of oil, which is constantly carried by the refrigerant circulating in the system. So your system could be low, OR it could be that there is a restriction and the high side climbs too high, and the low side can't get enough pulled through the evaporator to relieve it. We don't know without getting a pressure reading from the high side. The pressures may be outside of the allowed limits, or the measuring sensor may be going bad. (Safety switch, transducer, they have many names). It would be very important to know the high side readings, jumping to the wrong conclusion on a guess could result in mechanical damage to the compressor. If you don't have a gauge set that can read high side too, maybe a trip to a repair shop could tell you the readings, many places offer a "free Ac check" which doesn't tell you much, but they might be nice enough to give you the numbers.All your basics are there, and working, but especially if the clutch cycles on and off repeatedly when the pressure on the low side dips below 20psi, it just tells me the problem is pressure related, a low charge or restriction somewhere. I see no need for electrical troubleshooting, but the high side pressure reading would tell us more of whats happening in there.If you like doing your own AC work and saving a bunch of money on diagnosis and service, you might be able to justify the cost of a cheap AC "Manifold gauge set" as they are called, that have hoses and gauges for both high and low side, and a third hose for threaded refill bottles or other stuff like sealants or vacuum pump. The cheapest gauges do not last long in active use, but they should work fine if you only need them occasionally, like for seasonal checkups on your own vehicles. The gauges are not necessarily as accurate as professional equipment, but "close enough" to reveal problems.
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Customer reply replied 7 years ago
I have a manifold guage set. I have used it to charge my system once before. I should have checked both high and low pressures. I will check the high side pressure and report back to you. Would it be ok for me to get back to you tomorrow morning and we can pick it up from there? Will you be available tomorrow?
Dodge Mechanic: Jan Andersson, ASE Master Tech replied 7 years ago
I'll be online on and off throughout the day today
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Customer reply replied 7 years ago
I warmed up the engine and checked the pressures. At start, the low side was about 29 psi and the high was 225 psi at idle. Reving the engine, pressure went to 15 low and 120 high. I revved the engine for awhile longer and got 20 low and 260 high. I have a video of the pressures changing while cycling but can't seem to attach it here. Maybe this thing is low on 134. Should I get a can charge it? I fear I have a leak. Do you recommend using the UV dye to find leaks?
Dodge Mechanic: Jan Andersson, ASE Master Tech replied 7 years ago
Yes on the dye, some recharge cans come with it. I use it every time I service a system, whether there is a leak or not. These pressure readings are great, thanks. Unfortunately they didn't give me an easy answer. Startup pressures look pretty good to me, but it shouldn't dip to 15/120, both are very low. FYI, The transducer (Safety switch) should turn the compressor off when HIGH side pressure dips below 16psi. Yours does not monitor low side. That explains why it still kept going at such low pressure. - Then all of a sudden you get 20/260, that's strange. Is the fan working good? When the condenser/radiator fan comes on, the pressures drop pretty significantly. If the fan was on consistently during these fluctuations, maybe you have a restriction somewhere. For the low side to go down from 29 to 15, the high side should have gone UP.... not down. You could also have air in the system, it makes it behave very weird, even show high pressure but low charge.In a case like this I would definitely recover the refrigerant and vacuum the system, refill and try again. It gets rid of air and moisture, and can sometimes flush out debris that could be blocking a small passage. This usually means a trip to a shop with a recovery/recycling machine and extra cost.You probably know that releasing refrigerant into the athmosphere is illegal, I just had to say it out loud. ;)Is your system a dual setup, with a second AC evaporator for the rear? That could explain some of the fluctuation, the two systems operate independently
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Customer reply replied 7 years ago
Yes.. I have a second evaporator in the rear. Fan does appear to be running the whole time. I have noticed big pressure differences when I shut down the rear AC but I didn't record any readings. If it would be helpful, I can get more pressure readings with only one evaporator running. Everything so far has been with both. I don't mind taking it to a shop for an evacuation and refill but I would like to make sure it's not something more simple that I can address rather than pay the big $$.Should I charge the system then?
If so, what low (or high) pressure should I target? (when is it full?)
Dodge Mechanic: Jan Andersson, ASE Master Tech replied 7 years ago
The thing is, the only correct way to fill it is by WEIGHT. Pressures vary too greatly, affected by many factors, so you can't go by pressure alone. If you have an unknown amount of refrigerant in it, you can't know how much more it needs to be "full". Your system takes 2.38lbs of refrigerant. Your expansion valves may be acting up a little but more so I think it may be a case of air and low charge. Air masks it. 260 is too high in my opinion for this vehicle, and 16 is too low. I'd like to see (at idle) something around 25-30 low side and 200-225 high side, very rough ballpark numbers. Depends on ambient temperature, airflow through the condenser etc..
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Customer reply replied 7 years ago
25-30 low / 225 high were the numbers I gave you this morning. They were done with the AC controls turned to max cold and max fan with recirculation on. Ambient air was 79°F.What's my next move?
Dodge Mechanic: Jan Andersson, ASE Master Tech replied 7 years ago
I like those numbers, but I'm puzzled by the other numbers you also saw. Those were much different.That should make pretty cold air. The larger pipe going into the evaporator should be really cold. That means the evaporator is cold, and you should get cold air in. If you still don't get cold air, it has to be a problem with the door controls. See if you feel the line getting cold. The skinny line could get very hot, be careful.
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Customer reply replied 7 years ago
Where's the best place to feel or measure the temp of the evaporator or line going to it? I have most of the lower dash apart. Can I access the evaporator (front or rear) easily to check temp? I know there is an evaporator thermistor which the ATC monitors. Shouldn't it be giving an error if that evaporator is not getting cold?
Dodge Mechanic: Jan Andersson, ASE Master Tech replied 7 years ago
I don't know if it would trigger an error. I don't know how it works. I would just reach for the silver colored hard lines in the engine bay, close to where they go through the firewall. The evaporator cores are pretty well sealed inside their plastic housings.
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Customer reply replied 7 years ago
I just tried to find some coolness anywhere near either one of the evaporators and could not find any. So I don't think it is cooling. Guages were still on and low is now 35 and high is 250 at idle. Any more ideas to try?
Dodge Mechanic: Jan Andersson, ASE Master Tech replied 7 years ago
The cores are well insulated, I doubt you would feel anything unless you got your hands on the metal core itself or the metal lines. I'd say its inconclusive still, when there is a pressure difference as great as that, it means somewhere its gotta be making cold. Maybe a a restriction somewhere where its not supposed to be. Following the hard metal lines from the compressor throughout the system, feeling the condenser up front etc. should reveal a clear difference in temperature where it changes from hot to cold. The line going through the firewall is the closest you can get to the evaporator core. Any part of the system inside the cabin will be boxed up and insulated so condensation water wouldn't go on the floor.
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Customer reply replied 7 years ago
ok... through much investigation underneath the van and not finding any really good place to feel temperature on a line I decided to go inside and I found out that if I remove the cabin air filter the evaporator is right behind it. So I can get a few fingers on it. So I'm running it now. Pressures pretty much the same (30/225) but the evaporator isn't the slightest bit cool. I would say it is completely ambient. Ambient conditions I would say are about 81°F.What do you think?
Dodge Mechanic: Jan Andersson, ASE Master Tech replied 7 years ago
The expansion valve is what "makes cold" by releasing high pressure refrigerant into the low pressure evaporator through a small metering orifice. In general terms: if you have normal pressure, but no cold, the expansion valve is not working. Without getting my own hands and eyes on it, that is my conclusion. Maybe have a shop confirm it to be sure, replacing it is a bit time consuming and you have to empty the system to do it.
Jan Andersson
Jan Andersson, ASE Master Tech
Category: Dodge
Satisfied Customers: 834
Experience: 20 years of automotive repair & modification, USA, Asian, Euro, old & new cars.
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