I am glad that I found this group. I hope to learn from everyone's experiences. I will try and keep this to the point. It is a 2009 with the 2.4L. If you jump the pressure switch it will not make the compressor work. If you jump the pins on the relay the a/c works perfect. Pressures are normal while it is running when the relay is jumped. The items I have changed. The compressor, relay, fuses. climate control on the center console. One of the pins on the relay is to supposed to become the ground when the a/c is on. I think it is pin 28 it does not go to ground. it maintains a very low voltage. I am not a mechanic and have been trouble shooting this for a while any help would be appreciated. Thanks!


I tried jumping it, but will change it to see what happens. Thanks for your help!


Hello, everyone. I have a 2009 Chevy HHR LT 2.4 with 148000 miles, I bought this car to tow behind an RV. I have been fixing all of the little problems and have now been stuck on getting the A/C to work. When I bought it the compressor was bad. So I change out the compressor Jump the pressure switch to charge it up. That still would not get the compressor to run. Next changed out all fuses, pressure switch and relays, still no power to the compressor. Bought a used climate controller for the dash still no power to the compressor. Brought it to the dealer they sold me the 2 computers under the hood and programed them. Still no compressor. The dealer then wanted to sell me the body computer with no guarantee that that would fixed the problem. I did not buy that one. Got it home and started tinkering with it and found that if I made a jumper from pin 85 to pin 86 on the A/C relay the A/C would work. The A/C works fine as long as you jump those 2 pins together. There is a low voltage reading on those two pins when the A/C is off of about 1.2 volts. I think it is supposed to be 0. Electrical problems are my weak point. I live in Louisiana and would drive to almost anywhere to get this fixed. Any help would be appreciated, even smart ass comments would at least make me laugh in this hot car.


I think one of the computers was the TCM and the other one is the one that sits in front of it at the fuse box under the hood. I have been lazy getting this fixed because of the winter, but summer is coming and now it is a priority. I think I have it charge correctly. because if I jump the relay to get the compressor running the air coming out of the vent is at 40 degrees F. Thanks for any help!


I am not a certified mechanic, but have been working and rebuilding cars my whole life. I am 65 now and still screw up things all the time. I tend to go overboard when working on somethings. As for as the vacuum, I let the pump run for around and hour, then blocked it in and the negative pressure held for around 45 minutes. I added refrigerant then jumped the relay and used most of the 1 pound can getting the pressures up to 42 low side and around 180 high side. the air coming out of the vent was 40 degrees F. Took the jumper off and replaced the relay and then the compressor would not work.Then I unplugged the pressure switch at the compressor and jumped it and still the compressor would not work. I plugged the pressure switch back up and jumped the relay again and everything started working again, same pressures and temp coming out of the vent. I do appreciate you take the time to help me with this. Thanks again!


You could be right, my electrical skills are my weakness point. I will try and figure out where the wires are you are talking about are. I bought this car used and yes someone has been doing some wiring motivations I see some bypass wiring on the ignition fuses. I would like to find someone that could fix this. The Chevy dealer has me into this for almost 1800 dollars and still wants me to pay more with no guarantees. I do appreciate you trying to help me out Thanks!


Thanks for the advice>


Hello, everyone. I have a 2009 Chevy HHR LT 2.4 with 148000 miles, I bought this car to tow behind an RV. I have been fixing all of the little problems and have now been stuck on getting the A/C to work. When I bought it the compressor was bad. So I change out the compressor Jump the pressure switch to charge it up. That still would not get the compressor to run. Next changed out all fuses, pressure switch and relays, still no power to the compressor. Bought a used climate controller for the dash still no power to the compressor. Brought it to the dealer they sold me the 2 computers under the hood and programed them. Still no compressor. The dealer then wanted to sell me the body computer with no guarantee that that would fixed the problem. I did not buy that one. Got it home and started tinkering with it and found that if I made a jumper from pin 85 to pin 86 on the A/C relay the A/C would work. The A/C works fine as long as you jump those 2 pins together. There is a low voltage reading on those two pins when the A/C is off of about 1.2 volts. I think it is supposed to be 0. Electrical problems are my weak point. I live in Louisiana and would drive to almost anywhere to get this fixed. Any help would be appreciated, even smart ass comments would at least make me laugh in this hot car.

 

You replaced everything but the one part that has been proven bad; the pressure switch.

 

FYI. Posting this in the Premium Members section it’s going to get very limited views or responses. Trying posting it in one of the Problem forums if looking for help.
What computers were replaced ?

So. Where ya been for the last few months ?

 

You think you have it charged correctly ? How long did you pull vacuum on the system ? What were the pressure readings after charging ? If you only changed the compressor, then you may still have debris from the old compressor.
If you know how to correctly work on automotive AC’s then great. If not, then find an auto AC shop.

 

Unclear if it is fixed now?
When did this start? What positions are the switches in? Is the blower on? Has anyone messed with anything behind the waterfall (center dash).
There is a wire from the fan switch that goes to the BCM to tell it the blower is on. Could be that wire or the switch is faulty.

 

'if I made a jumper from pin 85 to pin 86 on the A/C relay the A/C would work.'

The PCM uses inputs from the pressure and temperature sensors to determine grounding the relay which is what you did by jumping it.
The dealer should have used a scan tool to see what the inputs are doing. Something as simple as ambient temp being to low will do it.

 

Ambient Air Temperature Sensor

The ambient air temperature sensor is a 2-wire negative temperature co-efficient thermistor.

A 5-volt reference and signal circuit enables the sensor to operate. As the air temperature surrounding the sensor increases, the sensor resistance decreases.

The sensor operates within a temperature range of -40°C to +60°C (-40°F to +140°F). The HVAC control module receives a class 2 message from the instrument panel cluster (IPC). The ambient air temperature sensor is mounted in the forward engine area, behind the left front headlamp. This causes an air flow issue due to the sensor's location and can effect the ambient air update display parameter in the DIC of the vehicle. For model year 2008 the ambient air temperature sensor will have a new location closer to the grill airflow. In the present position, it is exposed to limited airflow from the grill before it reaches the radiator. The sensor signal varies between 0-5 volts. The HVAC control module converts the signal to a working temperature range.

The ambient air temperature sensor algorithm uses 3 pieces of information, outside air temperature data, vehicle speed, and time the engine was turned off.

The ambient air temperature is updated and displayed by the DIC under the following conditions:

 

The ambiemy air temp has nothing to do with the AC. As shown on the chart, it only displays.
The ECM uses the IntakeAirTempemperature, part of the MAF sensor.

Did you mean to post this in another thread?

 

I think denhamhhr thinks this is a BBS from last century; they seem to be editing the OP instead of making a new post on reply.
I am now totally confused..

 

I am confused also, Does anyone work on theses cars for a living on this site. I am tiered of paying the dealership and not getting the problem fixed.