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post #1 of 14 Old 07-25-2017, 12:28 AM Thread Starter
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Recharging AC with 2 evaporators?

So, my 08 honda odyssey is low on freon and I charge it myself. It also has a front and rear ac/heater. The 2 combine exceed the btu listing of the compressor. Sometimes it seems to cool better with both on, other times front only.

Well, with both on the low side easily exceeds 100 psi even low. When I got the van it was like shy of 145 psi. When its just front only it behaves like any other car ac and hovers around 40 psi full.

I asked, but the dealer recharges a preset amount from empty and that seems to be the same online. Who knew backyard mechanics had their own recovery machine to pull, draw a vacuum and reinstall by weight?

So, just wondering what other guys do when they diy. Notice a lot of ac pro youtube videos and they seem hit or miss if they turn on both or front and many sart with a zero psi reading on the low side.
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post #2 of 14 Old 07-25-2017, 04:49 AM
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I'd have to see how the system is laid out. You won't get any cooling if the lowside is 100+ psi as you have no pressure drop to make the liquid turn into a gas. The 40 makes sense, how much is the highside?

You haven't done anything to tilt internal volume like add oil have you?

I would think at charging time you would have both going at once. Need to know if there is some kind of a switching valve in there that physically cuts one system out to not have one side seeing both orifices or expansion valves.

I charge using both gauges and around 25-50 on low side and up to 300+ high but the high depends heavily on ambient temperature. Volume means nothing to me as you simply go to correct pressures and done and the unit freezes your butt off then. I use a dead 5000 BTU window a/c unit 110V compressor as the vacuum pump and an empty 30# freon tank as what I pump any extra into out of unused in a can. My 'recovery unit'. I pay nothing for a/c work.

FYI, there is literally NO WAY you can accurately charge using only one gauge, there being whopping numbers of issues you will not have a clue about by doing that. Like here, having anything near 145 on low side would have me saying stop until I see that high side. It could be enough to blow the compressor into pieces.

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post #3 of 14 Old 07-26-2017, 02:28 AM Thread Starter
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Its basically a Y connection. So if you are low on freon the rear only works as its lower on the food chain vs the front.

I can get a gauge set, but never knew or can see online how that would help. I know for residential ac you use the temp scale of the high side vs actual temp of the liquid side to the temp rating of the unit.

It seems for autos its either the low side reading on those auto store units or a weight measurement from an empty system to a full recharge.

Yeah, when the rear ac is turned on the low psi side climbs off scale of those auto store units. When I got the van it too read high with both, but with front only it seemed to be on par with most cars.

Ive used those store cans with cold side gauges for years and usually end up passing around the bottle in the parking lot to my friends and co workers who have ac problems and the low side rears lower than it should.
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post #4 of 14 Old 07-26-2017, 10:29 PM
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Need to know both high and low to know what the system is doing. You need to get it evacuated and charged with the right amount of freon.

Pressure that high on the low side is either going to be too much charge in the system or you could have a bad expansion valve( if that system has one) but without knowing the high side you're in the dark.



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post #5 of 14 Old 07-27-2017, 02:20 AM Thread Starter
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My bad, tried it again on low side gauge. Pressure dropped 15 psi on low side when rear ac was also turned on. I added enough freon to make the low psi up 15 units.

30 vs 45 psi in 85 degree weather.
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post #6 of 14 Old 08-19-2017, 08:48 PM Thread Starter
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So, parked the Oddy as the Versa has an over all icy cold AC and my room mate did not mind riding in it. Went to take the Oddy for a spin today and FIrst off no AC. Turned AC off and on and it worked. Had his happen before assuming it was a memory thing of the electric system where the AC is delayed for a minute or 2 when frst start up.

Ac not exactly blowing cool or cold. Turn everything off and front only. Then it started blowing cold. Then turned on rear and still cold. Shopped at walmart for a few hours and had cold air in the parking lot. Lost cold air at advance auto. Got a can of freon and the low side was off the chart. Stuck a pen in the low side and as some of the freon blew out the ac compressor started up and had ac again. Turn on rear twice and it blew hot, turn it off it blows cold.

Checked psi on low side and when the rear is turned on the psi climbs off scale and the compressor kicks off. I tried rear only and same thing. Im guessing expansion valve is stuck open? I believe freon flows through the whole circuit rather or not the rear blower is on and turning it on controls the blower and vent flaps.

I understand if its low on freon the rear blows cold and front blows hot.

So, does this sound right that the rear expansion valve is stuck open?
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post #7 of 14 Old 08-20-2017, 09:16 AM
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Pick up a book and read, your ideas about a/c are hilariously funny, and no insult intended. Like this...........

'I know for residential ac you use the temp scale of the high side vs actual temp of the liquid side to the temp rating of the unit.'

The high side and the liquid side are the SAME THING, and WTF does your last 6 words there mean? NOTHING, goofy. Residential gets charged close to the very same way a car does BTDT.

The high side can run from 150 psi all the way to 300+ and you still be getting 40-50 psi on the lowside, why you CANNOT set the levels correctly like that. Your low will still be around the same, it CANNOT tell you anything doing that other than when things are major messed up. Using lowside only to set cooling on a good working system is a joke and how you got to where you are now........................LOST.

The HIGH side is what you temperature match to, NOT the lowside as it is pretty much worthless there, the pressure will be close to the same since it is the low and pressure to temp varies less there.

If you have two expansion valves then BOTH ends should be getting the same cooling. A stuck open valve lowers cooling as the pressure differential across it is lower, cooling occurs because of pressure drop not flow. One stuck open then messes the other up since the overall pressure drops even on the other one, but it depends on how much compressor capacity you have.

I say again......................the ONLY real rock-solid-works-every-time way is to use both gauges to measure both sides at same time, the relation of what one does as compared to the other tells you much.

If you have not bled every single time you add refrigerant then by now you probably have air and by extension water in the system and half your trouble can come from that. What eventually happens to all a/c DIYers.
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post #8 of 14 Old 08-20-2017, 01:19 PM Thread Starter
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Thanks bro. I just wanted free advice. Its 60 bucks to have the honda dealer look at it or 60 bucks for a 134a only gauge set. Since it sounds like it may need service and I have no way to remove, store and refill my ac system that is eco friendly Ill give it to the dealer.

The rear ac/heater I loved in previously owned vans and this one is a refustercluck. Seems Honda designed it to blow heat through the floor vent and ac over head automatically. Since my floor vents are removed it makes for a cold ride in the winter.

Plan B was to just use the front AC and save the rear for heat.

I got charged 500 bucks for home ac for 2-3 lbs of freon. Since it was an 08 model and used the older freon they wanted to replace vs fix or look for a leak or switch the freon to another brand. I purchased a gauge set but didnt have the connectors. Been researching how to do that too.

Ive had a received/dryer that clogged on my dodge wagoneer. The low side would build psi then as the ac compressor cycled on it sucked it to zero and stopped and the process repeated.
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post #9 of 14 Old 08-21-2017, 07:37 PM
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You sound young. If you intend to work on your own cars, the $60 pays for itself the first time you use it. The dealer? That $60 only whetted his appetite, the charges commonly go WAAAAY over that. They usually tell you you need max cost parts like compressor or evaporator to involve whopping install charges too. While those parts CAN go bad I've found that doing my own usually commonly only involves the refrigerant charges and nothing else. I made up a vacuum pump out of a common small window air conditioner compressor, you can find one anywhere.

Most people tear up the major parts by driving car too long, if you stop at the first sign of parts failing you never tear anything up in a major way. Why I've always had at least 3 cars running at all times, so I don't get trapped into that 'I have to have the car today to get to work' thing that puts so many of them in the scrapyards.

Last edited by amc49; 08-21-2017 at 07:51 PM.
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post #10 of 14 Old 08-22-2017, 01:37 AM Thread Starter
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FUrther testing reveals I need to fix another issue first. Its a wheelchair accessible van that kneals, ramps out, etc. I ve had issues with dead batteries, low batteries, etc. Long story short honda says the odyssey only needs 9 volts to crank and run. VMI who made the conversion says they need 13+volts for the wheelchair stuff to work. So, after sitting or the battery going low the sliding door works, but nothing else.

Ive replaced both batteries to have the emergency power system to fail. Other than driving the van daily the wheelchair dealer suggest installing a trickle charger. I notice when the ramp wont work if I turn on the lights or ac even on lowest setting the wheelchair stuff will work.

So, got a battery/alt tester and plugged it in. Cranked up van and turned on both acs to high. The power reaidng quickly fell and the radiator fans started to slow. The low psi side which was the only side I was measuring was going high. Then ac compressor popped off. Voltage starts to climb and process repeats.

So, do I get a new, rebuilt or an aftermarket high output alternator? I believe its a 130 amp in there. Mechman has an adjustable voltage regulator and the new square wire design. Rockauto has a reman denso for 200 bucks.
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