tuna55
tuna55 MegaDork
9/3/15 10:28 a.m.

Catywampus; a 1988 Honda Accord with OE R12 A/C converted by some PO to R134a. No stickers explaining who did it or when. No cooling, clutch and fans engage properly when commanded.

Running pressures 0/110 (the low side is slightly negative)

I added a can of R134a and got... 0/110

Engine off pressure is 85 psi or so both sides. It took hours to equalize.

Help. The static pressure tells me that it's full, the running pressures tell me that it's low. I am thinking the PO put too much oil or humid air into the system and now I have to evacuate and refill, thoughts?

t25torx
t25torx Dork
9/3/15 10:35 a.m.

I would think pulling a vacuum would be the safe route. So you know where you are starting from.

tuna55
tuna55 MegaDork
9/3/15 11:31 a.m.

Stuck expansion valve could cause zero or negative pressure on the low side, right?

I think the total capacity for the car is two cans. I added one and it didn't make a difference, so unless it had less than one can's worth when I started, it is full, which is supported by the 85 psi static pressure.

ProDarwin
ProDarwin UberDork
9/3/15 11:32 a.m.

Hmm. I would think evac and refill first to get a starting point.

Also check the pressure switch. The compressor should kick off far before it gets down to 0/110. Usually there is like a 20psi low-side cutoff.

Kenny_McCormic
Kenny_McCormic UltimaDork
9/3/15 2:17 p.m.

I'd suspect bad expansion valve/tube, and pressure switch.

tuna55
tuna55 MegaDork
9/3/15 2:33 p.m.

I don't want to add refrigerant, which costs money, because I can't collect it, just to diagnose it.

The pressure switch is an interesting idea. The clutch is always on when the AC button is on, could it be the sole cause of the 0 psi low side?

Dr. Hess
Dr. Hess MegaDork
9/3/15 2:52 p.m.

I would also suspect something is blocked in there. Surprised that the high side is not higher, though. Drier?

flatlander937
flatlander937 GRM+ Memberand Reader
9/3/15 3:17 p.m.

There is for sure a restriction, expansion valve or o-tube most likely a others said.

If a low pressure switch exists that is likely also bad. Or its like many cars where the high and low pressure switch are one in the same... It's not for the low side though, just for overall low/empty system safety. Not for this kind of situation.

While running feel the lines and check for extreme hot then extreme cold(or just kinda cool as bad as its restricted..). May not work if it goes STRAIGHT to zero though(if no refrigerant is circulating at all there won't be a temperature drop since none is getting by).

tuna55
tuna55 MegaDork
9/3/15 4:38 p.m.

From what I understand there's one pressure switch that does both high and low. For right now the compressor just stays on and does not cycle.

Checking under hood but I can't find any hot or cold places.

I think I can check but pressure switch against a zero psi if I evacuate the system.

Can I temporarily store the refrigerant an empty canisters? I mean I know I can I've done it accidentally but I don't know how much pressure they can hold before they make me bleed.

ProDarwin
ProDarwin UberDork
9/3/15 5:35 p.m.

You won't get a hot/cold difference because its not flowing. There is a restriction, its pumping the high side up to 110/pulling the cold side down to 0 and just sitting there. None of the high pressure gas is expanding to create cold.

Don't worry about the compressor staying on and not cycling... that's totally normal.

You have a clog in the system somewhere.. its pretty hard to diagnose without throwing parts or at least refrigerant at it :( Like others said, most likely the expansion valve/orifice tube.

Kenny_McCormic
Kenny_McCormic UltimaDork
9/3/15 5:49 p.m.

No, you cannot recover refrigerant at home, you either take it in for recovery (and they might not take from a questionable conversion) or just vent it.

I'd throw a drier/accumulator and expansion valve at it. Should be cheap on rockauto. The new drier should be charged with a something like 2-3 ounces of oil (see FSM), you'll want to use "ester" oil in a conversion, most parts stores will carry it. Replace any o rings you touch, an o ring kit for the car should also be cheap on rockauto.

tuna55
tuna55 MegaDork
9/3/15 7:23 p.m.
ProDarwin wrote: You have a clog in the system somewhere.. its pretty hard to diagnose without throwing parts or at least refrigerant at it :( Like others said, most likely the expansion valve/orifice tube.

Sorry, I wasn't trying to imply that I needed magic, just that the idea of vacuuming, buying two cans, charging, just to check it again didn't sound like the most efficient use of resources if we could point to at least one part to change while we were in there.

tuna55
tuna55 MegaDork
9/3/15 7:23 p.m.

I can understand the need to vacuum and recharge and change the expansion valve.

Why the drier?

Dr. Hess
Dr. Hess MegaDork
9/3/15 7:42 p.m.

If something clogged up/corroded the expansion valve, the drier must not be doing it's job anymore. They are not very expensive.

While You're In There with it all apart, flush out the coils. At very least, blow air through them and make sure they are not clogged up.

I Hate Automotive AC Systems.

Kenny_McCormic
Kenny_McCormic UltimaDork
9/3/15 8:31 p.m.

The drier is a cheap while you're in there, and as Dr. Hess noted, it's probably all used up at this point (can't realistically dry one back out). Plus they can do bad things with age, like fill the system with desiccant balls.

justdave
justdave New Reader
9/3/15 8:52 p.m.

Your readings are indicative of a stuck closed or clogged expansion valve (more likely) or a restriction/ clog in the evaporator or liquid line leading to the evaporator (less likely.) Your car has an expansion valve and not an orifice tube. The evaporator assembly will have to be removed to access/replace the valve. Is your car a DX,LX,or LXi? As to the repair procedure you have to ask yourself if you want the cheapest way or best way.

tuna55
tuna55 MegaDork
9/3/15 9:21 p.m.

In reply to justdave:

Hey thanks, it's an LXI.

The expansion valve is super easy to get to.

I'm thinking two cans of R134a, an expansion valve and a drier for a total of roughly $35.

I can handle that.

Kenny_McCormic
Kenny_McCormic UltimaDork
9/3/15 9:37 p.m.

In reply to tuna55:

Don't forget oil, and orings.

justdave
justdave New Reader
9/3/15 9:38 p.m.

There should be a silver sticker under the hood that will give you the R12 system capacity. As guide when converting to R134a use about 70% compared to the R12 fill. I started working at a Honda dealer in 1984 and the EX's had dealer installed factory air and would have had a Keihin compressor (not good) but if memory serves the LXi had a Matsus h i t a or Sanden unit. I can't see a Keihin making it this long as Honda started offering a swap /upgrade due to their high failure rate.

tuna55
tuna55 MegaDork
9/4/15 7:07 a.m.

In reply to Kenny_McCormic:

Why do I need oil if I vent off the refrigerant carefully, don't flush it, and don't replace the compressor?

tuna55
tuna55 MegaDork
9/4/15 7:07 a.m.

In reply to justdave:

Good memory. The good ones are Denso. Mine is. It's a remanufactured unit, so I suspect it was changed when whoever did the switch to R134a.

justdave
justdave New Reader
9/4/15 7:28 a.m.

I would not add anymore oil unless oil was removed. I would clean the core fins and replace the a.c. thermostat as well if I had the unit out for expansion valve replacement.

Kenny_McCormic
Kenny_McCormic UltimaDork
9/4/15 10:02 p.m.

In reply to tuna55:

The drier holds oil, when you replace it you put some oil in it, FSM will give the amount, but about 2 ounces/60ml should be right.

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