AC charging question

[Tony 69]

Don’t F with Bob, listen very closely

 

[Charrlie_S]

Don’t F with Bob, listen very closely

I would go by Jim in post #16 rather than Bob.

 

[RJRENTON]

Do you keep adding refrigerant untill you get to 34-36 degrees? what if you get to 40* and it doesn't go lower? Even if you get to 36* the head pressore could go to 300+ lbs. I have seen systems so over charged by DIY people the belt burned off the clutch with the hi side over 400 lbs. You are aware that with 134a the correct charge is actually Charge to about 75 % of the proper r-12 charge, then add a little more at a time allowing the system to stablize and watch the suction temp. keep adding untill the temp stops droping, and starts to increase, then remove about 1-2 OZ of refrigerant. With 134a it is better to be slightly under charged than over charged. R-12 was a lot more forgiving aboutb over charge.
PS: with a system with an EPR the chances have getting the evap air temp down to 34-36 degrees ain't gonna happen. The car in question "should" have an EPR valve.

I've done automotive A/C systems for years....yes...I'm well aware of the differences between R12 and R134A......it's called the specific heat characteristics which vary with temperatures and pressures as I'm sure you also know. I been always to able to achieve correct pressures/temps with an EPR valve (unless its defective) including the older GM system of Valves in Receiver (VIR) system and later the V5 variable displacement axial flow compressor and orifice tube refrigerant metering. What technique you use or your knowledge is up to you......I've had success with my technique......so whose is correct????......BTW....I use to do heat transfer and heat exchanger design.....especially hi temp gas to gas heat exchangers but to ASME SECTION VIII Division one......and the laws of thermodynamics.......I've likely read the same references as you have......
BOB RENTON

 

[Charrlie_S]

I've done automotive A/C systems for years....yes...I'm well aware of the differences between R12 and R134A......it's called the specific heat characteristics which vary with temperatures and pressures as I'm sure you also know. I been always to able to achieve correct pressures/temps with an EPR valve (unless its defective) including the older GM system of Valves in Receiver (VIR) system and later the V5 variable displacement axial flow compressor and orifice tube refrigerant metering. What technique you use or your knowledge is up to you......I've had success with my technique......so whose is correct????......BTW....I use to do heat transfer and heat exchanger design.....especially hi temp gas to gas heat exchangers but to ASME SECTION VIII Division one......and the laws of thermodynamics.......I've likely read the same references as you have......
BOB RENTON

OK. If you want references. Started doing auto AC in the 1960's. Even workd on the GM"s that had the old 5 cyl compressor, and Chryslers with the trunk units. No formal engineering training, but have been to GM training center for AC (plus others) several times over the years. Have built and installed many auto AC units that did not have kits available, Work as a "free lance" AC installer for several new car dealers back in the "80's. Worked for several AC speciality shops over the years. Attended both Trane, and Carrier training courses (for residential AC). Class "A' Industrial maint tech specializing in climate/humidity control. multiple hundred ton absorbtion units. Designed and built mobile refer units for Delivery vans. Got my section 609 cert in 1993 and my 608 universal cert in 1994. Before I retired, I was a ASE certified master auto tech, a jouryman tool and die maker, as well as my AC experiance. Also a member of the IATN since 1997. I am not getting involved with R-1234YF as I don't have the equipmet or the traing on it. Isn't feasable to invest in it for part time work. Plus I think I have enought stock of R-12 and R-134a to last me for what is left of my life, doing part time work on "collectables".

 

[RJRENTON]

OK. If you want references. Started doing auto AC in the 1960's. Even workd on the GM"s that had the old 5 cyl compressor, and Chryslers with the trunk units. No formal engineering training, but have been to GM training center for AC (plus others) several times over the years. Have built and installed many auto AC units that did not have kits available, Work as a "free lance" AC installer for several new car dealers back in the "80's. Worked for several AC speciality shops over the years. Attended both Trane, and Carrier training courses (for residential AC). Class "A' Industrial maint tech specializing in climate/humidity control. multiple hundred ton absorbtion units. Designed and built mobile refer units for Delivery vans. Got my section 609 cert in 1993 and my 608 universal cert in 1994. Before I retired, I was a ASE certified master auto tech, a jouryman tool and die maker, as well as my AC experiance. Also a member of the IATN since 1997. I am not getting involved with R-1234YF as I don't have the equipmet or the traing on it. Isn't feasable to invest in it for part time work. Plus I think I have enought stock of R-12 and R-134a to last me for what is left of my life, doing part time work on "collectables".

Your credentials are impressive....especially your experience with absorption chillers, like the old Bryant ammonia based residential chillers or lithium bromide industrial or NH3 commercial systems). Beside my high temperature gas to gas heat exchangers designs, I've also done gas to liquid and liquid heat exchangers. I'm hold a BS Electrical Engineering (Penn State), a MS in Business Administration (University of Pittsburgh) Macro Economics and a Registered Professional Electrical engineer credential.....but i managed an 85 man maintenance department at a chemical plant (all trades and crafts), but traveled the world over as a Project manager, building plants, installing capital equipment and machinery, for the companies I've worked for and in the late 60's, i flew the HU1D (with variations) during that conflict.....I flew the bird, 2 door gunners plus a copilot......in a time and galaxy far far away......which I don't care to talk about........automotive A/C systems is just a hobby.....I'm retired and keep busy as a Day Trader....for my own portfolio....to keep busy...but this is just me.....
BOB RENTON

 

[Mheiron]

No EPR valve installed. It’s sitting on the bench. NOS unit. I thought it wasn’t needed. The compressor is stock, rebuilt RV2. The system never seemed to get cold at the air vents. Just maybe a little cool. I’ll post more photos of the EXP valve setup tomorrow. When the valve was removed it seemed to have restricted flow. But I thought that was normal, the AC technician didn’t think so,he wants to try a bigger valve. It seemed to me the compressor was sucking more gas than could be squeezed past the valve, hence the low pressure on suction side.

Thanks for all the input, very much appreciated!

 

[Charrlie_S]

Your credentials are impressive....especially your experience with absorption chillers, like the old Bryant ammonia based residential chillers or lithium bromide industrial or NH3 commercial systems).
BOB RENTON

Never worked on amonia chillers. The units I worked on were the lithium bromide, and steam powered Chilled water units. They ran in a vacuum and used water as a refrigerant. As I said I don't have a "formal" education (never finished high school, just GED) Just trade schools, on the job training, and reading tech manuals. Think we need to get back to the Problem on hand. We have both tooted our own horns enough.

 

[Charrlie_S]

No EPR valve installed. It’s sitting on the bench. NOS unit. I thought it wasn’t needed. The compressor is stock, rebuilt RV2. The system never seemed to get cold at the air vents. Just maybe a little cool. I’ll post more photos of the EXP valve setup tomorrow. When the valve was removed it seemed to have restricted flow. But I thought that was normal, the AC technician didn’t think so,he wants to try a bigger valve. It seemed to me the compressor was sucking more gas than could be squeezed past the valve, hence the low pressure on suction side.

Thanks for all the input, very much appreciated!

Without the EPR valve, if the system is working properly, there will be no way to prevent evap freezeup when less then max load is on the system. (the EPR valve is used to allow better humity control then can be achieved with a clutch cycling system. The expansion valve is supposed to have a restriction, This restriction is what converts the high pressure liquid to a low pressure liquid. The valve meters the amount of liquid refrigerant based on the pressure and temp of the refrigerant.

 

[Charrlie_S]

Without the EPR valve, if the system is working properly, there will be no way to prevent evap freezeup when less then max load is on the system. (the EPR valve is used to allow better humity control then can be achieved with a clutch cycling system. The expansion valve is supposed to have a restriction, This restriction is what converts the high pressure liquid to a low pressure liquid. The valve meters the amount of liquid refrigerant based on the pressure and temp of the refrigerant.

Suggest you go to Service Manuals – MyMopar
service manual AC sec 23 pg 18
This is for R-12, but the numbers are close enough to use for trouble shooting with R134a

 

[RJRENTON]

No EPR valve installed. It’s sitting on the bench. NOS unit. I thought it wasn’t needed. The compressor is stock, rebuilt RV2. The system never seemed to get cold at the air vents. Just maybe a little cool. I’ll post more photos of the EXP valve setup tomorrow. When the valve was removed it seemed to have restricted flow. But I thought that was normal, the AC technician didn’t think so,he wants to try a bigger valve. It seemed to me the compressor was sucking more gas than could be squeezed past the valve, hence the low pressure on suction side.

Thanks for all the input, very much appreciated!

FYI....the TXV (Thermostatic Expansion Valve) handles or meters LIQUID refrigerant to the Evaporator....it could be restricted or inoperative.....starving the Evaporator causing insufficient cooling or if stuck open, it could cause flooding and potentially slugging the compressor with unevaporated liquid refrigerant. Some TXVs are pressure balanced as well as thermally controlled......just make sure you get the correct valve.......just a thought.......
BOB RENTON

 

[Charrlie_S]

FYI....the TXV (Thermostatic Expansion Valve) handles or meters LIQUID refrigerant to the Evaporator....it could be restricted or inoperative.....starving the Evaporator causing insufficient cooling or if stuck open, it could cause flooding and potentially slugging the compressor with unevaporated liquid refrigerant. Some TXVs are pressure balanced as well as thermally controlled......just make sure you get the correct valve.......just a thought.......
BOB RENTON

That system should have a external pressure balance tube. That's why I asked for a picture of the valve, and its connection. Also to make sure the temp sensing probe is in the suction line "well".

 

[Mheiron]

As you see we cut and plugged the pressure balance tube as part of our trouble shooting which seemed to have no effect. Our plan is try a larger valve next. We had our gauge cluster lined up per the SM.

 

[Charrlie_S]

I doubt your original problem was the expansion valve, but it is a problem now. I would have to dig out my part/spec book o tell you what valve you need. Most likely a 2 ton exteraly equilized for R134a but I'm not sure of the super heat spec'. Also you need to install the EPR valve. You never did post how much charge you installed before deciding you had a problem.
The expansion valve must have the pressure line connected. The factory had the temp sensing probe inserted into a "well" in the suction line. The well had heat conductive grease in the well (same stuff used to heat sink electronic modules). If you had aftermarket replacement hoses made and don't have the well, use that "coil" and clamp it to the metal part of the suction line, and cover with insulation.

 

[RJRENTON]

I doubt your original problem was the expansion valve, but it is a problem now. I would have to dig out my part/spec book o tell you what valve you need. Most likely a 2 ton exteraly equilized for R134a but I'm not sure of the super heat spec'. Also you need to install the EPR valve. You never did post how much charge you installed before deciding you had a problem.
The expansion valve must have the pressure line connected. The factory had the temp sensing probe inserted into a "well" in the suction line. The well had heat conductive grease in the well (same stuff used to heat sink electronic modules). If you had aftermarket replacement hoses made and don't have the well, use that "coil" and clamp it to the metal part of the suction line, and cover with insulation.

The pressure balancing connection is the capillary tube that is connected to the TXV below its control diaphragm. The capillary tube controlling the TXVs open/close is above the diagram assembly....hence the term pressure balanced. The gas in the controlling capillary tube is/should have similar characteristics as the refrigerant being controlled to achieve the correct response.....just my opinion....
BOB RENTON