Auto A/C question

[TankedUp]

Hey all. I have an aftermarket, Old Air Products, under dash A/C in my 85 K5. It doesn’t seem to be cooling properly. I don’t know much about a/c systems, so here is what I can figure out. Borrowed a/c gauges from work low side is 25 and high is 250 at 85 degrees outside air temp. Both lines in and out of evaporator coil are cold and both will form nice ball of ice after a while of running. Cold air out vents gets down to about 50 degrees on thermometer in vent, I have a thermal curtain hanging behind front seats so just trying to cool small part of interior. The temp in truck stays warm. Slightly cooler inside than outside truck. If anyone has any ideas to improve this a/c let me know.
Thanks

 

[JoshHefnerX]

sounds like you're getting some heater air mixed in, blend door maybe.. Be curios to see if you bypassed the heater to see if the temps dropped at the vent. If you're getting ice on the lines the evaporator should be getting cold.

 

[TankedUp]

Thanks. yea I forgot to mention the valve in heater lines is working and both hoses stay cool from valve to a/c box.

 

[6872xtc]

How is the airflow from the vents? Low airflow for the heatload in the cab won't be comfortable. With an evaporator that will ice up, I would believe that you should be fine at 85*.

How much insulation is on the floor? One of the biggest mistakes I see guys do is to strip out the insulation. Then the heat from the drivetrain and exhaust will cook you slowly.

 

[TankedUp]

Hey thanks. I should have made first post longer but didn’t. Anyhow here is long version. Air seems to blow pretty good till things start freezing up. Turn off compressor for few airflow pick back up and switch it back on. New rubber floor with jute backing, noco heat and sound insulation on roof and thermal curtain behind front seat. No tint on side windows. Think I should have sprung for vintage maybe bigger evaporator coil. I don’t know. Just thought it would be better than what I’m getting.
Still thanks for ideas.

 

[Wes Harden]

You shouldn't have a freezing evaporator. Air can't flow through a block of ice. Unsure of the system controls at this point I'm guessing, but I expect the Thermal Expansion Valve is suck open. Or the sensing tube does not have good contact with evaporator, or is broken.
25 psi on the low side is to low. 25 psi basically equates to 25°.
So when you turn the system off you are basically doing the thermal expansion valves job. It monitors the evap temp and closes the flow when the evap gets to @ 35-36°.
what year or model Old Air system do you have. I will be able to look it up and see what style control they used.

 

[imiceman44]

Hey thanks. I should have made first post longer but didn’t. Anyhow here is long version. Air seems to blow pretty good till things start freezing up. Turn off compressor for few airflow pick back up and switch it back on. New rubber floor with jute backing, noco heat and sound insulation on roof and thermal curtain behind front seat. No tint on side windows. Think I should have sprung for vintage maybe bigger evaporator coil. I don’t know. Just thought it would be better than what I’m getting.
Still thanks for ideas.

If I remember correctly when the system starts freezing up, it is a little low on refrigerant.
It happened on my reefer unit on my commercial trailer a few years ago.
We did a full service and it was good.

 

[TankedUp]

You shouldn't have a freezing evaporator. Air can't flow through a block of ice. Unsure of the system controls at this point I'm guessing, but I expect the Thermal Expansion Valve is suck open. Or the sensing tube does not have good contact with evaporator, or is broken.
25 psi on the low side is to low. 25 psi basically equates to 25°.
So when you turn the system off you are basically doing the thermal expansion valves job. It monitors the evap temp and closes the flow when the evap gets to @ 35-36°.
what year or model Old Air system do you have. I will be able to look it up and see what style control they used.

This is one I have. MPC-8212E-DS back in Dec 2016. 3 years back had a shop that vacuumed the system and they changed expansion valve didn’t seem to didn’t make a difference in operation so I just quit using it. there is a knob with a temp probe in evap coil. But I just leave it set where it is. Maybe I need to twist on that one. Thanks.

If I remember correctly when the system starts freezing up, it is a little low on refrigerant.
It happened on my reefer unit on my commercial trailer a few years ago.
We did a full service and it was good.

OK. Maybe I’ll throw a can of Freon in it see what happens. Thanks.

 

[Wes Harden]

With a high pressure of 250 I have my doubts.
When you put the gauges on, if system hasn't been run and engine is cool, both gauges sould show pressures @ ambient. Examp 85 psi should be about 85 ambient. Humidity has some effect.
Going to look up your kit

 

[Wes Harden]

What was the ambient temp when you checked the pressures ? Is your system charged with 134A ?
Old Air does show the kit components. But if you had it changed it chances are it is good .

 

[6872xtc]

It sounds like it has an adjustable thermostat for the evaporator core. I saw this with a Vintage air system. You have to adjust it to keep it from freezing.
I wouldn't put any freon in, I never saw a system freeze up from being low. The high side pressure won't get up enough to freeze.

 

[JoshHefnerX]

^^^ I added a vintage air unit to my old firebird and did have an adjustment knob.

https://www.vintageair.com/instructions_pdf/900001.pdf

 

[TankedUp]

OK Guys. Thanks for all these replies. I was sent to Louisiana and worked about 3 days straight finally made it home at 330 this morning. I didnt havetime to even look on here.

With a high pressure of 250 I have my doubts.
When you put the gauges on, if system hasn't been run and engine is cool, both gauges sould show pressures @ ambient. Examp 85 psi should be about 85 ambient. Humidity has some effect.
Going to look up your kit

What was the ambient temp when you checked the pressures ? Is your system charged with 134A ?
Old Air does show the kit components. But if you had it changed it chances are it is good .

it was 85 degrees don’t know humidity. I will go by and check it today. Much cooler here and lower humidity due to cold front. It is 134A.

low refrigerant level will absolutely cause an evaporator to freeze up. It causes low pressure in the coil allowing moisture in the air to accumulate and freeze.
you stated both lines are cold. Only the suction line should be cold. The liquid line should be warm, not cold.

as mentioned above by Wes, the sensing bulb should have good contact and be insulated. I’d start there as that’s easy to rule out.
next I’d look to the rotary evaporator control knob and try adjusting that. Clockwise is colder.

can you show a pic of the sensing bulb?

I have the old air kit as well. Not a fan of it. I had to manufacture and modify too much to make it work. If I didn’t have the tools and experience to know what needed to be done I would have returned the whole thing.

Both lines are cold to my touch. One was not as cold. But definitely not warm. Bulb has black gooey tape warped around it to hold it to line. I will try to unwrap it and get a pic. Yea I’m not impressed with this a/c.
Will have some overtime pay and sold some vacation. So have a bit of extra cash to maybe swap to something different. But the other systems seem to have good and bad reviews, just like this one had. I know vintage is pretty popular. Anyone that had a good experience with another brand let me know.
Thanks

 

[TankedUp]

OK. Here we go. Gonna have lots of pics.

temp 83 and humidity 52, says HaHa but that’s low for here.


so here is open hood hook up gauges way higher than air temp so should I let some Freon out? Too much since it’s so high?


OK. Now start-up turn on A/C


Now after five min idle time.


So while I wait for ten minute here is what I’m trying to cool.
Thermal curtain behind seats. Roof covers with noco,?, insulation stuff and vinylfloor with jute backing.


Ten minutes. Starting to get frosty on both sides. Taking longer today. I’m guessing lower humidity?

I watched high needle climb to 240 for second then drop back off pretty quick. Is that the thermal valve open and closing?
Anyhow I’ll let it go for another 5 if you need any more info let me know.
Ohh after 10 min getting warmer.

 

[Wes Harden]

ok I don't see anything that makes me go, thats wrong. the high side frost is on the evap side of the valve, that is normal. High side pressure cycling is normal. the problem is your low side is to low. So there need to be an adjustment somewhere. to cycle the compressor on and off. Is there an electrical sensor, either pressure or temp in the system ?

Yes with higher humidity your evap will freeze up sooner

 

[Wes Harden]

If were mine after you get working better, I add more black gooey stuff, to where you get frost. Can get a whole roll at O'Reilly's for under $20

 

[TankedUp]

OK. Compressor never shut off while it ran for 15 min or so that truck ran. it has that knob on unit under dash should I turn it till compressor cycles off and on?

before I came back and checked this thread I checked gauges I let it idle about 15 min and been shut off since. Just looked at gauges now and both show around 60. Why is it lower now than earlier? outside Temp now 85. I guess I will never understand a/c.

 

[TankedUp]

 

[bradshawtech]

I’m going with restricted or not ducted properly air flow. You should be seeing 32 degree air with those pressures

 

[TankedUp]

I’m going with restricted or not ducted properly air flow. You should be seeing 32 degree air with those pressures

OK. I have a diy4x dash but I will pull the hoses off box and see what temps are there. The vents on the dash are kinda small but seem to have lots airflow. Thanks. I’ll post up results.