Low side ~ 10psi, compressor stays on, no cycling.

cross6 on Mon June 22, 2015 10:34 PM

Year: 1999
Make: Honda
Model: Civic EX
Engine Size: 1.6 SOHC
Refrigerant Type: R-134a
Ambient Temp: 97
Pressure Low: 10
Pressure High: 300
Country of Origin: United States

This has me stumped. I am not familiar with Honda systems/Sanden scrolls.

Nephew brought his 99 Civic EX 1.6 SOHC (D16Y8) with Sanden Scroll over. He bought it recently.

Complaint: Barely cooling.

Initial findings:
Condenser Fan: Always runs with compressor. OK.
Compressor clutch: Engages smoothly. OK
Ambient Temp: 95 Degrees (F)
Center Vent Temp @ 2000rpm: 80 Degrees (F)
Low Side Pressure @ 2000rpm: 9-12 psi.
High Side Pressure @ 2000rpm: 300-400. (Slowly climbs with heat up and duration of run.)
Static pressures: Equalize to within a few PSI of each other in a normal amount of time.
Low side hose: Ambient temp
High side hose: Super super hot. Like engine block/manifold hot.
When compressor engages, the low and high begin to move away from static at a normal pace.

The low pulls down to about 9psi, and will hover between 9 and 12ish. THE COMPRESSOR DOES NOT CYCLE. It runs continuously.
The high side goes to about 300 during the same duration. Then begins to climb as engine bay/condenser heats up. Once it gets above 350 it begins to move quick.
I let it go to see if the cutoff would work and it hit about 425 before my assistant could turn it off.
Low side stayed low during this.

My initial thought was air/and or moisture in system. This was a recently purchased used car,
so who knows what monkey business went on. I found leaking schraders. Luckily I had some new sanden valves that fit.
Lubed them with nylog when system was empty and installed. No more leaking.

I never saw so much as a trace or vapor of oil or UV, which has me worried. Usually these little
japanese systems at least emit the smell of pag vapor when opening up. Or from the exhaust of my vac pump.
So I added 0.5 ounces of UV+PAG 46. I did not have a receiver/drier on hand or I would have swapped it. But this was mostly for diag purposes.

Refilled system with 2 cans r-134a. Underhood sticker says 21-22ounces. I'm an aggressive line purger
between cans so I lose several ounces. So two cans for me should be on the money.

Result was the same. I recovered a few ounces and the high side came down to about 250-300 while low side remained at 9-12psi
Compressor still ran continuously. Never cycled. Still 80 degree vent temps.

Sprayed hose on condenser, high side came down to about 200. Low side unaffected. Vent temps still 80 degrees.

This compressor shouldn't even be engaging at that low psi, right?
I found what looks like the pressure switch in the drier. I didn't see any
jumper wires or anything.

Not sure what my next step should be. It seems like to me the compressor is compressing like a champ if it can do 9/400+ ?
I'm thinking evac, replace drier and pressure switch. Drill and drain old drier to check for possible debris/contamination?

Metal Man on Mon June 22, 2015 11:14 PM

Have you checked the temperature control valve? Its located in the heater hose that feeds the heater core.Those cars are known for have problems with the valve not completely shutting the hot water flow to the core.

cross6 on Mon June 22, 2015 11:45 PM

Quote
Originally posted by: Metal Man
Have you checked the temperature control valve? Its located in the heater hose that feeds the heater core.Those cars are known for have problems with the valve not completely shutting the hot water flow to the core.

That won't cause 9/400 on the gauges. I'm not even worried about vent temp at this point.

Jag987 on Tue June 23, 2015 1:15 AM

My guess, and it is just a guess, partially closed/stuck/plugged expansion valve. they are fairly inexpensive and I know they are not bad to do considering it is in the evap box. I did one a few weeks ago on a 98 civic when it got a new compressor. the valve is not allowing refrigerant to get past it, so it all stays on the high side. Once it starts to heat up, it heats up quickly and the pressure jumps.

-------------------------
I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!

mk378 on Tue June 23, 2015 7:52 AM

There's a blockage somewhere. It could be the TXV, or the condenser or the receiver drier. Often a blockage in a part before the TXV will make an abnormal cold spot on one of the high side parts right after the blockage.

This is a TXV system. The compressor is not supposed to cycle on low side pressure. Indeed, there is no switch or sensor at all on the low side. Compressor will cycle off on evaporator temperature. The pressure switch (on the high side) cuts off at about 450 to prevent blown hoses or compressor damage.

Edited: Tue June 23, 2015 at 7:53 AM by mk378

cross6 on Tue June 23, 2015 9:48 AM

Quote
Originally posted by: Jag987
My guess, and it is just a guess, partially closed/stuck/plugged expansion valve. they are fairly inexpensive and I know they are not bad to do considering it is in the evap box. I did one a few weeks ago on a 98 civic when it got a new compressor. the valve is not allowing refrigerant to get past it, so it all stays on the high side. Once it starts to heat up, it heats up quickly and the pressure jumps.

Yep, I see it one of those units you can get to from the glove box area. I think I'll pick up a UAC TXV for $11, pull the old one and look for evidence of debris. If no debris I'll put in the cheap TXV to see if things change. If it improves I'll go ahead and get an OEM Denso one.

cross6 on Tue June 23, 2015 9:50 AM

Quote
Originally posted by: mk378
There's a blockage somewhere. It could be the TXV, or the condenser or the receiver drier. Often a blockage in a part before the TXV will make an abnormal cold spot on one of the high side parts right after the blockage.

This is a TXV system. The compressor is not supposed to cycle on low side pressure. Indeed, there is no switch or sensor at all on the low side. Compressor will cycle off on evaporator temperature. The pressure switch (on the high side) cuts off at about 450 to prevent blown hoses or compressor damage.

Ah ok. I spent way too much time chasing my tail about low pressure cutoff cycling. Can you tell I'm used to working on Fords?

Orifice tube operation is hard wired in my brain.