Cold in town, warmer on Highway

Moderators: Nacho, Tom Greenleaf, ACProf, acsource

Cold in town, warmer on Highway

Postby huntindog » Mon Aug 29, 2016 4:16 am

I did a compressor job on my brothers 85 Chevrolet K20. All new components. R12
I had two sets of specs on the charge. One said 44 oz, the other 48 oz. To make matters worse, the stock condenser is no longer available. The aftermarket replace looks OK, but is different. Not sure how that will affect the capacity.
We put in about 3.5 12 oz cans. It cooled well on city streets , but was warmer on the highway.Low pressure was about 38 , high 180 about 90 degrees out. I guessed a slight overcharge, and took a little out Temps improved, but the compressor low cutout switch wasn't working.. It got as low as 36 at the vent, (at night) and no cutout. Put a new switch on and no change.. Grasping at straws, my brother started removing what looked like factory tape around the wires going to the switch. He found the problem. someone had stripped about 1.5" of insulation from both wires and twisted them together... Effectively bypassing the switch.
We redid the wiring, and checked the pressures About 85 degrees out, Low 32 @ idle, dropping to 29 @ 1500 rpm. High about 170.
We took a road test, and it still cools better on city streets than the highway.. We got down to 48 on the highway. 46 on city streets. The temp holds very well , and sometimes even drops a little at a red light....
The fan clutch is a new heavy duty one.
The high pressure line from the compressor to the condenser is hot. The line from the condenser to the orfice tube is close to ambiant. The evaporator inlet right after the orfice tube is cold, the evaporator oulet tube is colder. sweating a LOT, as is the accumulator, and the line going from it to the Compressor suction port.

I cannot see how it is possible, but it seems to still be a little overcharged???

Should the line be sweating at the point where it enters the compressor?
huntindog
 
Posts: 28
Joined: Mon Feb 17, 2014 1:42 am
Favorite Refrigerant: r12

Re: Cold in town, warmer on Highway

Postby Tom Greenleaf » Mon Aug 29, 2016 9:01 am

First you have to allow LPCO switch to work or risk choking compressor with returned liquid refrigerant and it will when cooler or if condenser is working very well.

General: I think you lower the charge for the newer condenser about 10 ounces and the part should have said so with information with the part.

Your pressures seem fine. IDK - as you need to know at what RPM you see that too.

At highway speeds if now cutting out and LPCO is working now it's possibly low on charge.

Sweating accumulator and return lines is normal for humidity at the time and conditions all around. Frost is not normal and you might be freezing up evaporator unseen on highway.

Getting charge just right when info is lost like this is hard to do. You need steady conditions and adjust up or down the charge till pressures and performance match up to expectations with the conditions and temps changing with the time you are doing that changes accounted for as well.

It can be done.

Nothing is going to matter if you leave cut out switch jumped when it chokes compressor so fix that first,

T
MetroWest, Boston
Image
______________________________
User avatar
Tom Greenleaf
 
Posts: 4549
Joined: Tue Jun 28, 2005 8:40 am
Location: Marlborough, MA. USA
Favorite Refrigerant: R-12+134a

Re: Cold in town, warmer on Highway

Postby huntindog » Mon Aug 29, 2016 2:22 pm

We fixed the switch yesterday. My brother works nights. He emailed me. Last night on his way to work "It maintained 48 on highway could hear compressor cycling that was with fan on 2/3 turned fan on high when I exited got down to 41 in the two miles to work".

The new condenser is still a tube and fin affair, but it is different.

Right now I am confused.
huntindog
 
Posts: 28
Joined: Mon Feb 17, 2014 1:42 am
Favorite Refrigerant: r12

Re: Cold in town, warmer on Highway

Postby Tom Greenleaf » Mon Aug 29, 2016 3:48 pm

I think you are good. 2/3rd fan, closed windows it's cycling because it's low side switch detects that and cuts out as it should. Try for fun just run fan on high, open a window a bit and compressor will stay working most likely.

The condenser game. IDK - Parts don't always look at all like the originals but must fit properly. Hope against hope if it alters something they put a paper in with it so say what.

So you think you saw outputs of 41 once and that's about all a system should do at very best no matter the temp. It's not meant to freeze evaporator - period.

I always question the real temps folks observe. Just me but not thrilled with the meat thermos for vents nor ambient air temps you really are dealing with and use wired digital remotes matched and checked. Now hard to find the exact ones I like not for automotive but fast and accurate! Cheap too.

I say something is off if true temp of air coming in thru grille can't drop temp to center vent by at least 40F even the times it can spike over 100F it's needs something. Doesn't happen for real where I am and stay at the 115F or more real temps I forgive the system and watching for engine temps.

I think you are all set,

Tom
MetroWest, Boston
Image
______________________________
User avatar
Tom Greenleaf
 
Posts: 4549
Joined: Tue Jun 28, 2005 8:40 am
Location: Marlborough, MA. USA
Favorite Refrigerant: R-12+134a

Re: Cold in town, warmer on Highway

Postby huntindog » Mon Aug 29, 2016 4:52 pm

This morning, my Brother called. On his way home from work, he ran the fan on high. On the freeway the temp got down to 43-44. Not sure on the clutch cycling as the combination of road noise and fan noise made it too hard to hear it. He has mud tires on the truck. On city streets the clutch was cycling off @ 41, temp would rise to 43-44 and the compressor would engage again.
We are using digital fast acting probe type thermometers.

I still think it may be a tiny bit overcharged due to the highway vent temps being higher than the city temps. But we are going to leave it alone.
huntindog
 
Posts: 28
Joined: Mon Feb 17, 2014 1:42 am
Favorite Refrigerant: r12

Re: Cold in town, warmer on Highway

Postby Tom Greenleaf » Mon Aug 29, 2016 6:49 pm

Higher on highway only when air speed is enough without a fan?

OK - It's possible that fan clutch isn't working properly meaning it might still be pulling too hard and air speed already forced thru grille at highway speeds should be coasting freely.

A good high quality "thermostatic" one should let go and almost coast by hand a couple revs of the blades engine off but run recently just a bit.

When cool like highway if still pulling hard it could fight with incoming air and actually slow it down!

Other not common for this style is the silly air dam that you don't even notice under the bumper may be missing totally. I think they were a rubber like thing but fairly stiff.

If missing and air can force UNDER vehicles instead of a slight vacuum so air flow thru grille, down and out it's not going to get the best air flow.

Usually or more likely an issue with really aero dynamic cars that sit low those or now all plastic bumpers bust up from just the parking bumpers used in many places. They are all over the sides of roads sometimes here damaged by crusty snow banks even.

Worth a check on both,

Tom
MetroWest, Boston
Image
______________________________
User avatar
Tom Greenleaf
 
Posts: 4549
Joined: Tue Jun 28, 2005 8:40 am
Location: Marlborough, MA. USA
Favorite Refrigerant: R-12+134a

Re: Cold in town, warmer on Highway

Postby Cusser » Tue Aug 30, 2016 3:01 pm

huntindog wrote: On the freeway the temp got down to 43-44. On city streets the clutch was cycling off @ 41, temp would rise to 43-44 and the compressor would engage again.

I still think it may be a tiny bit overcharged due to the highway vent temps being higher than the city temps. But we are going to leave it alone.


I think leaving it as it is now - that's a good idea.
User avatar
Cusser
 
Posts: 494
Joined: Wed Jun 29, 2005 4:22 am

Re: Cold in town, warmer on Highway

Postby huntindog » Tue Aug 30, 2016 4:25 pm

I got this email this morning:
40.2 on my way to work with fan on high then the compressor started cycling never went above 44
I think we're done. 8)

Sent from my iPhone
huntindog
 
Posts: 28
Joined: Mon Feb 17, 2014 1:42 am
Favorite Refrigerant: r12

Re: Cold in town, warmer on Highway

Postby Tom Greenleaf » Tue Aug 30, 2016 5:17 pm

Sounds right. Just leave it alone with those observations,

Tom
MetroWest, Boston
Image
______________________________
User avatar
Tom Greenleaf
 
Posts: 4549
Joined: Tue Jun 28, 2005 8:40 am
Location: Marlborough, MA. USA
Favorite Refrigerant: R-12+134a


Return to A/C Questions and Opinions

Who is online

Users browsing this forum: Bing [Bot] and 9 guests