Heater core heating up A/C evaporator coil???

[Greenlee]

I have spent a small fortune in the last year replacing just about every component of the A/C system on my 76'. New compresor, new lines, new dryer, etc. However, I still don't think it blows as cold as it should. On a hot day in Houston I have to leave it on high and it's just a little more comfortable than driving with the windows down.

This week I had it checked by a couple different A/C places who told me it was full of freon and should be working fine. The last guy I took it to had a theory that the hearter core is heating up the evaporator coil. He said they are in close proximity to one another and the doors that control air flow from the heater or A/C probably aren't opening and closing like they should on a truck this old. Another guy told me something similar about a year ago and said he put a valve in the line to the heater core to bypass the heater on his Chevelle.

My question is, has anybody else had this problem? Also, what is the best solution for the problem? I put a valve in the line from the radiator to the heater core last night, and drove it to work this morning and didn't notice much of a difference with that line blocked. Did I put the valve on the right line? Do I also need to block the line from the heater core to the engine?

[Slonaker]

Originally Posted by Greenlee

On a hot day in Houston I have to leave it on high and it's just a little more comfortable than driving with the windows down.

Mine gets pretty comfortably cool. It does sound as though something is not right.

Originally Posted by Greenlee

I put a valve in the line from the radiator to the heater core last night, and drove it to work this morning and didn't notice much of a difference with that line blocked. Did I put the valve on the right line? Do I also need to block the line from the heater core to the engine?

I have considered doing the same thing to see if it makes a difference. I might be wrong, but I think you put the cutoff in the wrong hose. I believe that the water goes into the radiator through that section of hose. I seem to recall seeing water dump into the radiator from there when the radiator is low. That would mean that you put it after the heater core, and the heater core is still full of hot water. Anyone else have an opinion on this?

Slonaker

[454HO]

I don't think it should matter whether the valve is on the input or the output of the heater core. It should block the flow either way.

Greenlee, has this a/c been converted to R-134a? If so, running water over the condensor while the truck is idleing with the a/c on. If your vent temps drop, then you need a more efficient condensor or at least more airflow across your current condensor.

[Greenlee]

Originally Posted by 454HO

Greenlee, has this a/c been converted to R-134a? If so, running water over the condensor while the truck is idleing with the a/c on. If your vent temps drop, then you need a more efficient condensor or at least more airflow across your current condensor.

He used FREEZE 12, which I am told may be some sort of hybrid of the old R12 and 134a. You may have a point about air flow as it cools down a bit at speed on the freeway.

[454HO]

Originally Posted by Greenlee

He used FREEZE 12, which I am told may be some sort of hybrid of the old R12 and 134a. You may have a point about air flow as it cools down a bit at speed on the freeway.

What are you using for a radiator fan? Do you have a shroud? Clean all the bugs out and straighten the fins on the condensor? I've never used the Freeze12 stuff, but it's supposed to be as good as R-12. Do you know what pressures you have on high and low side? Maybe it's overcharged?? Does the pipe going from the evaporator to the drier frost over, or at least get condensation on it? It should be very cold if the system is working right.

The temperature lever in the dash controls the position of the diverter valve that directs air flow over the heater core. This is operated by a cable behind the dash connecting the lever to the valve. You should be able to look underneath there and see it move as you slide the lever from COLD to HOT.

All the other vents doors and flappers work off of engine vacuum. Have you made sure you are getting a good vacuum signal to the control switch in the dash to operate them? Slide the control switch from OFF position to DEF position stopping at each position in between. You should hear the flappers and vent doors move between each position. Also make sure air is directed to the appropriate outlet.

[Greenlee]

Originally Posted by Slonaker

I have considered doing the same thing to see if it makes a difference. I might be wrong, but I think you put the cutoff in the wrong hose. I believe that the water goes into the radiator through that section of hose. I seem to recall seeing water dump into the radiator from there when the radiator is low. That would mean that you put it after the heater core, and the heater core is still full of hot water. Anyone else have an opinion on this?

I could have it on the wrong line. I pondered it for a while and figured the top line was the inlet, but I do not know. The top line looks a little biger than the bottom line. I think the top line is 3/4" and the bottom is 5/8".

I drove it again at lunch and it seems a little cooler, but its not a dramatic difference. I also had the windows tinted yesterday so that's probably helping a little. It just doesn't seem as cold as it should be to me.

[jermasaurus]

Easy thing to check is to see if your evaporator is getting clogged in between the fins. I think you can pull the blower motor out and check it.

If you have a infared thermometer of know somebody who does here is a rule of thumb strait out of the book...
Your outlet line from the condensor should be 30-60 degrees cooler than the inlet.
The evaporator outlet line should be no more than 5 degrees cooler than the inlet.
Any more or less directs you to another flow chart in the book.

If you suspect a restriction, you can record the line temperature at various points throughout the system (hoses, condensor, etc.) If you have a restriction, you would find an increase in temperature from one point to another. Obviously this wouldnt apply where the high and low sides seperate at the compressor.

[a28doc]

the way the heater core works is water from the radiator goes to the engine then thru the heatercore after it gets sufficiently heated then back to the radiator to cool down again before it starts its journey over again.If you remove the heater core cover you should be able to inspect the airflow door to see what needs replaced or oiled even might work on the pivot points. the cover is fairly simple to remove in our style trucks hope this helps ... Doc

[ureckme]

There is 2 vent doors one is in back of the glove box that switches from A/C to heat. Some times the door doesn't close all the way, to get to it remove glove box and theres a cover w/3 screws. Slide cover off and check the vent door to see if its close'n all the way ( truck must be running w/AC on ) runs off vacume.
2 the other vent door is in the right side kick panel next to glove box. This one takes vacume to open, if it's closed it wont blow much air. If the doors are not working you may have a vacume leak, bad vacume switch, or bad vac/ pods that move the vent doors. The valve on the heater hose is a good idia too.

[Earl Filter]

You should really do what I'm about to do, before my truck is in running/driving condition, and I do some A/C work: Get certified to buy R12, and have your system vacuumed and recharge it with R12. That Freeze 12 may be OK for a top off of an R12 system, and may work for a complete recharge, but I bet you money there's your problem. Go here:

www.epatest.com

You want section 609. It's online study, and an OPEN BOOK test, where you can look up the answer. Then, go to ebay, or wherever, and buy your R12! YES you can buy R12 with the certificate that you get from the EPA. Want to know what it's going for if you're certified? $20 or less per 12oz can on average is what I'm seeing. I've seen 30# cylinders on there, but they bring about $400. But hey, if you've already spent a fortune, why not go all the way and get the real stuff? It's what your system was made for, and Freeze 12 is never going to do the job that R12 Freon will!

[jermasaurus]

A 30lb of r12 for $400? that is really cheap. A 30lb of 134a is up to about $250. From what I have heard, there were 3 places in the U.S. making 134a and 2 of them shut down.
By the way, I wouldnt really buy freon on ebay. Usually when somebody buys a large quantity you would test the purity of the freon on the spot.
There are some honest people occasionaly though.

[Earl Filter]

Yeah, it may be more like $500 or so, but that's still a lifetime supply for the average Joe.

Here's a couple to watch:

A case (12 - 12oz cans)-

http://cgi.ebay.com/ebaymotors/ws/eB...979972498&rd=1

A 30# cylinder-

http://cgi.ebay.com/ebaymotors/ws/eB...979161669&rd=1

It's like anything else on ebay...check the seller's feedback, read the ad, etc. I'm very careful, but have never been burned on ebay, or buying stuff from individuals off of various auto forums.