AC after a swap (factory ecm)

[DarrinWI]

Last fall I finally hooked up and charged my ac after the swap. I’ve run into two issues that I’m hoping someone may be able to help me troubleshoot, or at least point me to where I should look.

Following the instructions on LT1swap.com, I created new wire runs for the ac controls into the ecm. Issue #1- When I turn on the ac, if I connect the low pressure switch, the compressor runs on every position on the hvac control. If I unplug the low pressure switch, it comes on as it should with just the ac selection

Issue #2- my fans aren’t turning on with the ac. This caused me to blow the high pressure relief valve while sitting in traffic on Sunday.

On Monday I verified that my wires are running to the correct ecm pins. It started pouring rain before I could investigate the relay wiring. But could there be something else I should look at?

For the fans, I know that I have to verify they are switched on for ac in the tune. I can’t remember if I requested that when I sent away for the initial tune. Is there something else o should look for?

Thanks for any help/direction.

 

[L05edSS]

not sure this will help in any way cuz i had a ac delete during a motor swap and the high fan setting didnt work on the heater my case turned out to be a bad ground for others i seen it turned out to be a bad relay. also the swap deleted all emissions equip.

 

[383_StealthRam]

Following the instructions on LT1swap.com, I created new wire runs for the ac controls into the ecm.

Which specific instructions are you referring to from that site ?

the compressor runs on every position on the hvac control. If I unplug the low pressure switch, it comes on as it should with just the ac selection

The compressor should run typically on MAX AC, NORM and BI-LEVEL as well as DEFROST modes.
What year/make /model car is this?
What does the HVAC control panel look like?
Again, with respect to how you created "new wire runs" we have no idea what that means without more detail?

I know that I have to verify they are switched on for ac in the tune. I can’t remember if I requested that when I sent away for the initial tune. Is there something else o should look for?

Did you contact who did the tune for you and ask if that was done? If you're wiring things up to the PCM with the expectation it will control the fans a certain way, (at x psi, for example) you definitely need to confirm the tune is configured for that.


There's multiple schools of thought on hot rods with AC, and how they should (or shouldn't) integrate with the EFI computer controls for the compressor clutch, and cooling fans. I won't get into them all here, but suffice to say most like to keep it simple and usually let the AC system work independently from the EFI system. Typically most EFI systems do have the ability to take an input that the AC is turned on, and use that to make an increase in idle speed, or trigger the fans, cut out the compressor under certain conditions like WOT etc. These functions all require proper wiring and programming to be in place.

Alternatively, most will simply install a "trinary" switch into their AC system in order to provide protection against both LOW and HIGH pressure conditions. For example if the pressure in the system is too low, you don't want the compressor to come on because it could be damage with no refrigerant flow and lubricating oil. Similarly you don't want the compressor to stay engaged if there is a blockage, or not enough air flow over condenser which could cause compressor damage, or hose to leak, etc.

A trinary switch get's wired inline to the compressor's clutch control circuit so it protects it from the above.

Additionally the trinary switch will have a second pair of wires that can use the pressure in the high side of the AC system to trigger a power or ground for your electric fan relay(s) so the come on and go off as the AC pressure rises and falls. The difference in trinary switch vs. EFI PCM control is the former are usually pre-set while the latter you can program to suit your needs.

Vintage Air, and some other brands make them and I recommend them in cases like yours where you may not be hands on, or have the tools/software/skills to do the necessary OEM PCM HVAC controls integration. (ie, the appropriate MPVI OBD port device for something like HP Tuners to read, edit and write tune changes.) Additionally any required licensing that is required.

HTH

 

[DarrinWI]

Which specific instructions are you referring to from that site ?


The compressor should run typically on MAX AC, NORM and BI-LEVEL as well as DEFROST modes.
What year/make /model car is this?
What does the HVAC control panel look like?
Again, with respect to how you created "new wire runs" we have no idea what that means without more detail?


Did you contact who did the tune for you and ask if that was done? If you're wiring things up to the PCM with the expectation it will control the fans a certain way, (at x psi, for example) you definitely need to confirm the tune is configured for that.


There's multiple schools of thought on hot rods with AC, and how they should (or shouldn't) integrate with the EFI computer controls for the compressor clutch, and cooling fans. I won't get into them all here, but suffice to say most like to keep it simple and usually let the AC system work independently from the EFI system. Typically most EFI systems do have the ability to take an input that the AC is turned on, and use that to make an increase in idle speed, or trigger the fans, cut out the compressor under certain conditions like WOT etc. These functions all require proper wiring and programming to be in place.

Alternatively, most will simply install a "trinary" switch into their AC system in order to provide protection against both LOW and HIGH pressure conditions. For example if the pressure in the system is too low, you don't want the compressor to come on because it could be damage with no refrigerant flow and lubricating oil. Similarly you don't want the compressor to stay engaged if there is a blockage, or not enough air flow over condenser which could cause compressor damage, or hose to leak, etc.

A trinary switch get's wired inline to the compressor's clutch control circuit so it protects it from the above.

Additionally the trinary switch will have a second pair of wires that can use the pressure in the high side of the AC system to trigger a power or ground for your electric fan relay(s) so the come on and go off as the AC pressure rises and falls. The difference in trinary switch vs. EFI PCM control is the former are usually pre-set while the latter you can program to suit your needs.

Vintage Air, and some other brands make them and I recommend them in cases like yours where you may not be hands on, or have the tools/software/skills to do the necessary OEM PCM HVAC controls integration. (ie, the appropriate MPVI OBD port device for something like HP Tuners to read, edit and write tune changes.) Additionally any required licensing that is required.

HTH

Thanks for the info and the detailed response. I forgot to update this post. I did what you suggested. I added a high pressure switch in series with the low pressure switch going to the compressor which also feeds a trigger to on 17 of the ecm. I found another suggestion online and grounded on 53 so that completed the circuit alerting the ecm to the ac being called.

I by-passed the ecm for the fans, instead using my “ ac on and safe” feed to trigger a relay to call up the fans. It all works and has been field tested.

Now I’m chasing a P0300 random misfire code at highway speeds, but that’s a topic for a different post.

 

[383_StealthRam]

That's great, glad you got it worked out!!